Scientists genetically tweaked a tiny, worm-like parasite to produce a life-saving antitoxin from inside a living host.

In a first-of-its-kind study, researchers modified the hookworm Ancylostoma ceylanicum so that it produces antibodies that partially neutralize the potent pufferfish poison tetrodotoxin.

The approach has so far been tested in hamsters, but the ultimate aim is to use it in people. In fact, the study was funded by the U.S. Department of Defense with a view to developing protective treatments for military personnel exposed to chemical or biological threats, such as tetrodotoxin, study co-author Alex Loukas, director of the Australian Institute of Tropical Health and Medicine at James Cook University, told Live Science.

That said, future work could see these worms engineered to produce a variety of other medications and excrete them inside the human body, the study authors wrote in a report published June 3 in Nature Communications. For instance, they could deliver long-term treatments for chronic diseases, such as type 2 diabetes or inflammatory bowel syndrome, Loukas suggested.

From parasite to antitoxin factory

Hookworms are one of humanity's oldest parasites and infect upwards of 400 million people globally, primarily in tropical regions. Like an internal leech, these small intestinal worms latch on to the inner wall of the gut to feed on blood, simultaneously releasing a variety of anti-inflammatory and immunosuppressant compounds to prevent the body from flushing them out.

Each worm is about 0.4 inches (1 centimeter) long and consumes less than two drops of blood a day, and healthy hosts often don't experience any symptoms of infection. The hookworm used in this study, A. ceylanicum, infects humans, dogs and cats.

"The hookworm has spent millions of years perfecting how to assure long-term survival inside a human host and how to get molecules out of its body and into ours," study co-author Makedonka Mitreva, professor at Washington University School of Medicine in St. Louis, Missouri, said in a statement.

The cocktail of compounds produced by these parasites has already shown some promise in treating metabolic disorders such as metabolic syndrome and type 2 diabetes, as well as celiac disease. However, studies so far have been restricted to molecules produced by the hookworms naturally.

The new work pushes this concept one step further. "We asked: What if we could add one more molecule to the roughly 1,000 things the worm already secretes, something therapeutically useful to people?" Mitreva said. "This study shows that's not just a concept. It works."

Using CRISPR gene-editing technology, the team inserted a gene coding for an antibody known to counteract the deadly pufferfish poison tetrodotoxin into the hookworm's genome at the egg stage. Mitreva's team had to carefully consider the placement of the gene, ensuring it didn't interfere with other critical regions of DNA, yet still promoted production and secretion of the new protein.

The team then infected hamsters with 80 to 100 of the modified parasite larvae. Upon maturation, the adult worms containing the newly inserted gene were able to produce the antibody and then secreted it into the hamster's bloodstream. Blood samples later taken from the infected hamsters partially neutralized the tetrodotoxin poison in lab experiments, showing compounds produced by the worm were active in the hamster.

On paper, the same approach could be used to secrete other antibodies or peptide drugs — which are short bits of protein — to directly treat gastrointestinal disorders, Loukas said.

"We're thinking about actively introducing antibodies that neutralize inflammatory hormones or cytokines," to treat conditions such as inflammatory bowel disease, he said. "You can also think about the possibility of a worm that secretes very very small quantities of food allergens to desensitize the host for childhood food allergies,” he added.

Looking forward, the team wants to extend the durability of the therapeutic molecules the worms release, since they can only make so much at a time, he noted.

While it may sound counterintuitive to infect a person with a parasite to help them feel better, hookworms actually have an excellent safety profile, Loukas said. A quirk of their biology means there is no chance of the infection getting out of control.

Hookworm larvae enter the body through the skin and migrate to the small intestine where they mature into adults, often living for years without noticeably impacting the host. Any eggs the adult parasites produce must hatch outside of the host; they exit in the host's stool. That means the number of adult worms in the body remains fairly constant.

What's more, with a single dose of a standard anti-worming treatment, the infection clears within 24 hours. So any hookworm-based treatments could be easily cleared from a person's system.

"It's exciting and it's really opening up an entirely new way of delivering and producing therapeutic molecules," Loukas said.

Roman soldiers defending Hadrian's Wall in Britain were well acquainted with diarrhea and stomachaches, according to a new study that found evidence of at least three different intestinal parasites in the soil near centuries-old toilets.

The finding shows that Roman guts suffered greatly, in spite of the wall having what was then a state-of-the-art sewer system.

The auxiliary fort of Vindolanda in northern England was occupied by the Romans from the first through the fourth centuries. The fort stood just south of Hadrian's Wall, which was first built in A.D. 122 to protect the northernmost extent of the Roman Empire. Vindolanda is known for its oxygen-free layers of mud, which have helped preserve perishable material like writing tablets, leather shoes and even bedbugs for millennia.

In a study published Friday (Dec. 19) in the journal Parasitology, a team of researchers investigated a new line of evidence at Vindolanda — soil preserved in the drain pipes of the fort's third-century latrines.

Researchers collected 58 samples from along the length of the latrine drain, some of which contained animal bones, Roman beads and pottery. They then micro-sieved the soil samples to look for the eggs of parasitic worms.

Within the latrine samples, the researchers discovered eggs from roundworms (Ascaris sp.) and whipworms (Trichuris sp.). Both roundworms and whipworms are parasites that live in human intestines, often causing stomachaches, fever and diarrhea. These fecal-oral parasites are typically passed along when a person ingests unsanitary food or dirt contaminated with the parasites' eggs.

Additionally, in one sample, the researchers detected Giardia duodenalis, a parasite that also infects the small intestines and causes giardiasis or giardia infections.

The presence of all three parasites suggests fecal contamination of water or food sources at Vindolanda, the researchers wrote in the study. But while whipworms and roundworms have been identified before in Roman Britain, this is the first evidence for G. duodenalis.

"Archaeological sites in Britain dating to before the arrival of the Romans have not been systematically tested for Giardia," study co-author Piers Mitchell, a paleoparasitologist at the University of Cambridge, told Live Science in an email, so "it remains unknown whether this parasite was in the U.K. prior to the Roman period."

But Giardia is an important clue to the health of the people living along the Roman frontier.

"Of the three parasites we found, Giardia is the most likely to cause serious health problems," Mitchell said. While short-term infection results in diarrhea and dehydration, long-term side-effects of giardia infection can include irritable bowel, eye damage, arthritis, allergies and muscle pain.

Although Roman soldiers were not legally allowed to marry, myriad forms of archaeological evidence, including preserved children's shoes, point to men, women and children all living at Vindolanda. And the new parasite evidence may point to a major health concern for soldiers' kids.

"Diarrhea can lead to dehydration in all age groups, but it is young children who are most likely to die from it," Mitchell said. "Chronic infection in children with Giardia, roundworm or whipworm can all lead to stunted growth and reduced intelligence."

Gastrointestinal issues from parasites were likely quite common in most parts of the Roman Empire, the researchers noted in the study, but the new analysis does not reveal exactly how many people suffered from these infections.

"As the sewer drain contains the mixed feces of all those who used the latrine, we cannot tell what proportion of those at Vindolanda were infected by parasites," Mitchell said. Given data from past studies, though, it’s thought likely that "between 10 and 40% of people in Roman times were infected by intestinal worms."

Editor's note: This article was updated on Monday (Dec. 22) at 9:55 a.m. EST to correct the misidentification of roundworms and whipworms as microscopic.

Roman Britain quiz: What do you know about the Empire's conquest of the British Isles?

The patient: A 32-year-old woman in Shanghai

The symptoms: The woman went to the hospital with a persistent cough accompanied by occasional bloody phlegm, which she would cough up two to three times per day. She said the coughing began four months prior to her hospital visit. And about a month before the coughing started, she had a fever that lasted several weeks and reached up to 100.8 degrees Fahrenheit (38.3 degrees Celsius).

What happened next: Doctors at the hospital diagnosed the woman with a rare respiratory illness called eosinophilic pneumonia, an infection in which white blood cells accumulate in the lungs and cause inflammation. If left untreated, the infection can damage the lungs, and in some cases, it can be fatal.

The patient's doctors gave her steroids to reduce the inflammation in her lung tissue. However, her cough persisted even after two months of this treatment. A CT scan of her lungs revealed recurring lesions, or tissue injuries, and she was then sent to a different hospital for further examination.

The diagnosis: When doctors at the second hospital reviewed the woman's medical history, they noted that her diet often included raw seafood, and she also reported "a preference for raw frogs and bullfrogs," the physicians wrote in a report describing her case. The team conducted a blood test to see if her blood contained antibodies to any parasites, and they found antibodies for the larvae of Spirometra mansoni, a type of tapeworm.

The larvae, or spargana, of S. mansoni cause a parasitic infection called sparganosis. This infection is most common in eastern Asia, and people often acquire the parasites by eating raw or undercooked snakes or frogs that are infected with the larvae, evidence suggests. After S. mansoni larvae are swallowed, they migrate into various body tissues and organs. In the woman's case, they accumulated in her lungs — a very rare destination for the parasite.

When the patient provided doctors with a frog from her region of Shanghai, they dissected it and found that it was carrying S. mansoni.

Because the woman's symptoms and the results of her CT scans closely resembled signs of eosinophilic pneumonia, the physicians who examined her during her first hospital visit misdiagnosed her, according to the report.

The treatment: Doctors treated the woman with praziquantel tablets, a drug that works against various types of parasitic worms. After the woman had taken the tablets for five days, her coughing subsided.

CT scans performed 20 days after her admission to the second hospital showed that the shadowy areas previously seen in her lungs — a sign of infection or physical trauma — were shrinking. At a follow-up visit one month later, her coughing was completely gone. However, the patient's blood tests showed that she was still producing antibodies against the parasite, hinting that the infection persisted.

Doctors prescribed another five-day course of praziquantel and conducted a follow-up examination five months after that. Traces of antibodies remained in the patient's blood, but only in extremely low quantities. Her white blood cell count was normal, and the doctors determined that no further treatment was required.

What makes the case unique: Sparganosis infections typically appear in tissues located just under the skin, near the surface of the body. They rarely migrate to the internal organs. This is the first case to be documented in Shanghai of sparganosis in the lungs, the case report authors wrote.

Eating raw animal flesh is a long-standing cultural tradition in parts of Asia, and sometimes, small animals may be consumed while they are still alive. Living frogs are occasionally eaten as a folklore remedy for a variety of ailments; an 82-year-old woman in Hangzhou was hospitalized with a parasitic infection after she swallowed eight small, live frogs in an attempt to relieve her chronic back pain.

For more intriguing medical cases, check out our Diagnostic Dilemma archives.

This article is for informational purposes only and is not meant to offer medical advice.

Scientists analyzing 1,300-year-old human feces from the Cave of the Dead Children in Mexico have discovered that people often dealt with nasty intestinal infections more than a millennium ago.

"Working with these ancient samples was like opening a biological time capsule, with each one revealing insight into human health and daily life," study lead author Drew Capone, an assistant professor of environmental health at Indiana University, said in a statement.

Capone and colleagues used molecular analysis techniques to study 10 ancient desiccated feces samples — also called paleofeces — found in a cave in Mexico's Rio Zape Valley just north of the city of Durango in northwestern Mexico, that dated from A.D. 725 to 920. The researchers published their findings Wednesday (Oct. 22) in the journal PLOS One.

In the late 1950s, archaeologists excavated the Cave of the Dead Children and recovered human and non-human paleofeces, plant remains and animal and human bones from a large trash heap. The cave was used by people from the prehistoric Loma San Gabriel culture, who practiced small-scale agriculture, produced unique ceramics, lived in small villages and occasionally practiced child sacrifice. Archaeologists named the cave after the skeletons of children found there.

Previous studies of paleofeces from the cave revealed the presence of hookworm, whipworm and pinworm eggs, suggesting the people who deposited their feces in the cave were infected by a variety of parasites.

In the new study, the scientists used cutting-edge molecular techniques to detect additional microbes in paleofeces from 10 "distinct defecation events" with the aim of expanding their understanding of the burden of disease among the Loma people. "There is a lot of potential in the application of modern molecular methods to inform studies of the past," study co-author Joe Brown, a professor of environmental sciences at the University of North Carolina at Chapel Hill, said in the statement.

The researchers extracted DNA from the 10 paleofeces samples and then used polymerase chain reaction (PCR) to amplify the DNA of the microbes in the feces. Every sample had at least one pathogen or gut microbe in it, and the two most common were the intestinal parasite Blastocystis, which can cause gastrointestinal issues, and multiple strains of the bacterium E. coli, which were found in 70% of the samples. Also identified were pinworms as well as Shigella and Giardia, which cause intestinal illnesses.

The high number of microbes discovered in the paleofeces "suggests poor sanitation among the Loma San Gabriel culture from 600-800 CE resulted in exposures to fecal wastes in the environment," the researchers wrote in the study. People likely ingested the microbes via feces-contaminated drinking water, soil or food, the team added.

While these pathogen-associated genes persisted in the paleofeces for up to 1,300 years, there may have been even more pathogens in the samples that have since decayed and are no longer detectable, the researchers noted in the study.

Still, the new analysis revealed the DNA of pathogens that were not previously found in paleofeces, including Blastocystis and Shigella.

"The application of these methods to other ancient samples offers the potential to expand our understanding of how ancient peoples lived and the pathogens that may have impacted their health," the researchers wrote.

When you think about ticks, you might picture nightmarish little parasites, stalking you on weekend hikes or afternoons in the park.

Your fear is well-founded. Tick-borne diseases are the most prevalent vector-borne diseases — those transmitted by living organisms — in the United States. Each tick feeds on multiple animals throughout its life, absorbing viruses and bacteria along the way and passing them on with its next bite. Some of those viruses and bacteria are harmful to humans, causing diseases that can be debilitating and sometimes lethal without treatment, such as Lyme, babesiosis and Rocky Mountain spotted fever.

But contained in every bite of this infuriating, insatiable pest is also a trove of social, environmental and epidemiological history.

In many cases, human actions long ago are the reason ticks carry these diseases so widely today. And that’s what makes ticks fascinating for environmental historians like me.

Changing forests fueled tick risks

During the 18th and 19th centuries, settlers cleared more than half the forested land across the northeastern U.S., cutting down forests for timber and to make way for farms, towns and mining operations. With large-scale land clearing came a sharp decline in wildlife of all kinds. Predators such as bears and wolves were driven out, as were deer.

As farming moved westward, Northeasterners began to recognize the ecological and economic value of trees, and they returned millions of acres to forest.

The woods regrew. Plant-eaters such as deer returned, but the apex predators that once kept their populations in check did not.

As a result, deer populations grew rapidly. With the deer came deer ticks (Ixodes scapularis) carrying Borrelia burgdorferi, the bacterium that causes Lyme disease. When a tick feeds on an infected animal, it can take up the bacteria. The tick can pass the bacteria to its next victim. In humans, Lyme disease can cause fever and fatigue, and if left untreated it can affect the nervous system.

The eastern U.S. became a global hot spot for tick-borne Lyme disease starting around the 1970s. Lyme disease affected over 89,000 Americans in 2023, and possibly many more.

Californians move into tick territory

For centuries, changing patterns of human settlements and the politics of land use have shaped the role of ticks and tick-borne illnesses within their environments.

In short, humans have made it easier for ticks to thrive and spread disease in our midst.

In California, the Northern Inner Coast and Santa Cruz mountain ranges that converge on San Francisco from the north and south were never clear-cut, and predators such as mountain lions and coyotes still exist there. But competition for housing has pushed human settlement deeper into wildland areas to the north, south and east of the city, reshaping tick ecology there.

While western black-legged ticks (Ixodes pacificus) tend to swarm in large forest preserves, the Lyme-causing bacterium is actually more prevalent in small, isolated patches of greenery. In these isolated patches, rodents and other tick hosts can thrive, safe from large predators, which need more habitat to move freely. But isolation and lower diversity also means infections are spread more easily within the tick’s host populations.

People tend to build isolated houses in the hills, rather than large, connected developments. As the Silicon Valley area south of San Francisco sprawls outward, this checkerboard pattern of settlement has fragmented the natural landscape, creating a hard-to-manage public health threat.

Fewer hosts, more tightly packed, often means more infected hosts, proportionally, and thus more dangerous ticks.

Six counties across these ranges, all surrounding and including San Francisco, account for 44% of recorded tick-borne illnesses in California.

A lesson from Texas cattle ranches

Domesticated livestock have also shaped the disease threat posed by ticks.

In 1892, at a meeting of cattle ranchers at the Stock Raiser’s Convention in Austin, Texas, Dr. B.A. Rogers introduced a novel theory that ticks were behind recent devastating plagues of Texas cattle fever. The disease had arrived with cattle imported from the West Indies and Mexico in the 1600s, and it was taking huge tolls on cattle herds. But how the disease spread to new victims had been a mystery.

Editors of Daniel’s Texas Medical Journal found the idea of ticks spreading disease laughable and lampooned the hypothesis, publishing a satire of what they described as an “early copy” of a forthcoming report on the subject.

The tick’s “fluid secretion, it is believed, is the poison which causes the fever … [and the tick] having been known to chew tobacco, as all other Texans do, the secretion is most probably tobacco juice,” they wrote.

Fortunately for the ranchers, not to mention the cows, the U.S. Department of Agriculture sided with Rogers. Its cattle fever tick program, started in 1906, curbed cattle fever outbreaks by limiting where and when cattle should cross tick-dense areas.

By 1938, the government had established a quarantine zone that extended 580 miles by 10 miles along the U.S.-Mexico border in South Texas Brush Country, a region favored by the cattle tick.

This innovative use of natural space as a public health tool helped to functionally eradicate cattle fever from 14 Southern states by 1943.

Ticks are products of their environment

When it comes to tick-borne diseases the world over, location matters.

Take the hunter tick (Hyalomma spp.) of the Mediterranean and Asia. As a juvenile, or nymph, these ticks feed on small forest animals such as mice, hares and voles, but as an adult they prefer domesticated livestock.

For centuries, this tick was an occasional nuisance to nomadic shepherds of the Middle East. But in the 1850s, the Ottoman Empire passed laws to force nomadic tribes to become settled farmers instead. Unclaimed lands, especially on the forested edges of the steppe, were offered to settlers, creating ideal conditions for hunter ticks.

As a result, farmers in what today is Turkey saw spikes in tick-borne diseases, including a virus that causes Crimean-Congo hemorrhagic fever, a potentially fatal condition.

It’s probably too much to ask for sympathy for any ticks you meet this summer. They are bloodsucking parasites, after all.

Still, it’s worth remembering that the tick’s malevolence isn’t its own fault. Ticks are products of their environment, and humans have played many roles in turning them into the harmful parasites that seek us out today.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

The patient: A 41-year-old woman in Beijing

The symptoms: The patient went to the hospital because she felt like there was something stuck in her right eye. When doctors looked at her eye, they noted that its outer surface, the cornea, appeared damaged, but they didn't find any foreign bodies. They prescribed the patient eye drops, one type to treat the eye irritation and another with antibiotics in it to help prevent infection.

What happened next: The eye drops did not ease the woman's symptoms, and she returned to the hospital the next month with the same feeling that something was stuck in her eye. She also reported persistent eye redness and itchiness.

When doctors reexamined her eye, this time they noticed that the tissue beneath her upper eyelid looked inflamed and bore "significant" pimple-like bumps, they wrote in a report of the case. They used a device called an eyelid retractor to pull back the eyelid and more closely examine the tissue beneath.

The diagnosis: There, the doctors found four small, white worms wiggling around. The medical team applied a topical anesthetic — a medicine to numb the area — and then removed the worms with forceps, and sent the extracted worms to the lab. A microscopic and genetic analysis of the worms revealed that they were a species called Thelazia callipaeda, also known as the Oriental eye worm, which can cause a parasitic infection called thelaziasis.

The treatment: After extracting the worms from the woman's eyelid, the doctors rinsed her eye with a solution to "ensure no worms remained," they wrote in the report. She was also prescribed an eye ointment containing an antibiotic to use several times a day, which helped reduce the risk of a subsequent bacterial infection.

"One week later, the patient's symptoms were significantly relieved, and no recurrence was reported over the following two months," her doctors wrote.

What makes the case unique: Thelaziasis is relatively rare in humans. It's seen more often in animals, including cattle, dogs, cats, foxes and rabbits. The worms are transmitted to these animals via flies that carry the parasite. The flies feed on the animals' tears and deposit the worm larvae into their eyes as they do so. The larvae then mature inside the eye — often in the eyelid, specifically — before being picked up by another passing fly, continuing their life cycle. A variety of Thelazia species can cause the infection, but T. callipaeda is the most common culprit.

Historically, most cases of thelaziasis in humans have been reported in Asia, with China reporting the largest number overall. In the more than 100 years — between the country's first known human cases in 1917 and 2018 — just over 650 cases were reported.

"Thelaziasis cases have been reported mainly in agricultural areas and areas with high potential for contact with domestic animals," the report authors noted. Additionally, many people affected by the disease report being involved with animal husbandry and/or they specifically recall being recently exposed to flies.

In this case, though, the source of the woman's infection wasn't 100% certain. The patient was an office worker based in an urban center, and she didn't recall a recent exposure to flying insects. She did, however, report having a pet cat who'd recently had an eye infection. "Pathological examination of the cat was not performed as the patient refused," her doctors noted. So while the cat was the likely source of the worms, that wasn't officially confirmed.

The report authors concluded that, even in urban centers, doctors should be aware of the symptoms of thelaziasis and consider it as a potential diagnosis. Symptoms can range from mild to severe, including the feeling of something in your eye, itching, eye pain, bleeding or inflammation of the tissue covering the eye and eyelids, ulcers in the cornea, and vision changes. The parasitic infection can also be complicated by secondary bacterial infections, which worsen these symptoms. Doctors should ask about whether patients have pets or have had recent contact with flying insects, they added.

This article is for informational purposes only and is not meant to offer medical advice.

Scientists in China have discovered a host of never-before-seen viruses in bats that live near humans. These viruses include two that are closely related to the deadly Nipah and Hendra viruses, which can cause severe brain inflammation and respiratory disease in humans.

The work, published June 24 in the journal PLOS Pathogens, highlights the importance of keeping a close eye on bats and other animals that live near human populations, and avoiding contact with them as much as possible.

Bats are natural reservoirs for many pathogens that can cause disease in humans, but the full extent of the bacteria, viruses and other potentially infectious agents they harbor is not known. Most previous studies have focused on bat feces rather than on internal organs, mainly because it is easier to collect. However, that tells us only about the viruses that make their way into feces.

To investigate the pathogens present in bat kidneys, a team led by Yun Feng of the Yunnan Institute of Endemic Disease Control and Prevention sampled the kidneys of 142 bats from 10 species collected from China's Yunnan province. Genetic sequencing revealed 22 viruses, 20 of which had never been seen before, as well as a new protozoan parasite and two kinds of bacteria, one of which was new to science.

Study co-author Edward Holmes, a virologist at the University of Sydney in Australia, said focusing on the kidneys is important because they provide a window into what viruses might be excreted in urine, and urine is one way humans might be infected by bat viruses.

"Bats peeing into date-palm collecting bowls was how Nipah virus first spread from bats to humans," Holmes told Live Science. Because the bats in this study were living close to orchards near human villages, there is a risk that contaminated fruit could allow these pathogens to jump to livestock or people.

Although two of the new viruses are closely related to Nipah virus and Hendra virus (together known as henipaviruses), they are not cause for concern, Holmes said.

"These newly discovered viruses have not yet been found in humans, and there is currently no evidence that they will ever infect or emerge in humans," he said. "In theory, they could pose a threat, but as there are no human cases, there is no need to be concerned."

However, the discoveries do highlight the importance of sampling animals like bats that live near human populations. It would also be helpful to monitor human populations that might be exposed to these animals, to identify potential viral threats before they emerge.

"It is this increasingly porous animal-human interface that leads to pandemics," Holmes said. "Pandemics always reflect how humans disturb natural environments. Better surveillance is always the key."

Male fertility rates have been plummeting over the past half-century. An analysis from 1992 noted a steady decrease in sperm counts and quality since the 1940s. A more recent study found that male infertility rates increased nearly 80% from 1990 to 2019. The reasons driving this trend remain a mystery, but frequently cited culprits include obesity, poor diet and environmental toxins.

Infectious diseases such as gonorrhea or chlamydia are often overlooked factors that affect fertility in men. Accumulating evidence suggests that a common single-celled parasite called Toxoplasma gondii may also be a contributor: An April 2025 study showed for the first time that "human sperm lose their heads upon direct contact" with the parasite.

I am a microbiologist, and my lab studies Toxoplasma. This new study bolsters emerging findings that underscore the importance of preventing this parasitic infection.

The many ways you can get toxoplasmosis

Infected cats defecate Toxoplasma eggs into the litter box, garden or other places in the environment where they can be picked up by humans or other animals. Water, shellfish and unwashed fruits and vegetables can also harbor infectious parasite eggs.

In addition to eggs, tissue cysts present in the meat of warm-blooded animals can spread toxoplasmosis as well if they are not destroyed by cooking to proper temperature.

While most hosts of the parasite can control the initial infection with few if any symptoms, Toxoplasma remains in the body for life as dormant cysts in brain, heart and muscle tissue. These cysts can reactivate and cause additional episodes of severe illness that damage critical organ systems.

Related: 32 scary parasitic diseases

Between 30% and 50% of the world's population is permanently infected with Toxoplasma due to the many ways the parasite can spread.

Toxoplasma can target male reproductive organs

Upon infection, Toxoplasma spreads to virtually every organ and skeletal muscle. Evidence that Toxoplasma can also target human male reproductive organs first surfaced during the height of the AIDS pandemic in the 1980s, when some patients presented with the parasitic infection in their testes.

While immunocompromised patients are most at risk for testicular toxoplasmosis, it can also occur in otherwise healthy individuals. Imaging studies of infected mice confirm that Toxoplasma parasites quickly travel to the testes in addition to the brain and eyes within days of infection.

In 2017, my colleagues and I found that Toxoplasma can also form cysts in mouse prostates. Researchers have also observed these parasites in the ejaculate of many animals, including human semen, raising the possibility of sexual transmission.

Knowing that Toxoplasma can reside in male reproductive organs has prompted analyses of fertility in infected men. A small 2021 study in Prague of 163 men infected with Toxoplasma found that over 86% had semen anomalies.

A 2002 study in China found that infertile couples are more likely to have a Toxoplasma infection than fertile couples, 34.83% versus 12.11%. A 2005 study in China also found that sterile men are more likely to test positive for Toxoplasma than fertile men.

Not all studies, however, produce a link between toxoplasmosis and sperm quality.

Toxoplasma can directly damage human sperm

Toxoplasmosis in animals mirrors infection in humans, which allows researchers to address questions that are not easy to examine in people.

Testicular function and sperm production are sharply diminished in Toxoplasma-infected mice, rats and rams. Infected mice have significantly lower sperm counts and a higher proportion of abnormally shaped sperm.

In that April 2025 study, researchers from Germany, Uruguay and Chile observed that Toxoplasma can reach the testes and epididymis, the tube where sperm mature and are stored, two days after infection in mice. This finding prompted the team to test what happens when the parasite comes into direct contact with human sperm in a test tube.

After only five minutes of exposure to the parasite, 22.4% of sperm cells were beheaded. The number of decapitated sperm increased the longer they interacted with the parasites. Sperm cells that maintained their head were often twisted and misshapen. Some sperm cells had holes in their head, suggesting the parasites were trying to invade them as it would any other type of cell in the organs it infiltrates.

In addition to direct contact, Toxoplasma may also damage sperm because the infection promotes chronic inflammation. Inflammatory conditions in the male reproductive tract are harmful to sperm production and function.

The researchers speculate that the harmful effects Toxoplasma may have on sperm could be contributing to large global declines in male fertility over the past decades.

Preventing toxoplasmosis

The evidence that Toxoplasma can infiltrate male reproductive organs in animals is compelling, but whether this produces health issues in people remains unclear. Testicular toxoplasmosis shows that parasites can invade human testes, but symptomatic disease is very rare. Studies to date that show defects in the sperm of infected men are too small to draw firm conclusions at this time.

Additionally, some reports suggest that rates of toxoplasmosis in high-income countries have not been increasing over the past few decades while male infertility was rising, so it's likely to only be one part of the puzzle.

Regardless of this parasite's potential effect on fertility, it is wise to avoid Toxoplasma. An infection can cause miscarriage or birth defects if someone acquires it for the first time during pregnancy, and it can be life-threatening for immunocompromised people.

Taking proper care of your cat, promptly cleaning the litter box and thoroughly washing your hands after can help reduce your exposure to Toxoplasma. You can also protect yourself from this parasite by washing fruits and vegetables, cooking meat to proper temperatures before consuming and avoiding raw shellfish, raw water and raw milk.

This article was updated to remove an incorrect statement about the prevalence of deaths due to foodborne toxoplasmosis.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

Shocking new footage shows a pair of bloodsucking parasites latched onto the head of a deep-sea rattail fish.

In the video, which the Schmidt Ocean Institute shared in a Facebook post, two copepods — small crustaceans — are positioned on either side of their host's head. Long egg sacs attached at the back of the parasites make it look like the fish is sporting a pair of pig tails.

"They feed on blood and fluids from their host using their scraping mouth parts that are embedded in the muscle of the fish," James Bernot, an evolutionary biologist at Smithsonian National Museum of Natural History who was not on the expedition, told Live Science in an email.

Scientists captured the footage at a depth of 1,604 feet (489 meters) during an expedition to examine the seafloor and biodiversity of the South Sandwich Islands, a chain of 11 subantarctic volcanic islets in the South Atlantic Ocean.

The copepods are a species called Lophoura szidati, and are latched onto the head of a rattail fish from the genus Macrourus, representatives wrote in the Facebook post.

Related: Watch bright red blood-sucking parasite feast on gulper eel in rare, deep-sea footage

Macrourus are commonly known as grenadiers or rattails because of their large heads and slender tails. These widespread deep-sea fish occupy the cold waters of the North and South Atlantic Ocean, as well as the Southern Ocean that borders Antarctic waters, and can be found at depths from 1,312 to 10,450 feet (400 to 3,185 m).

Knowledge of deep-sea fish parasites in Antarctic waters is scarce, but L. szidati, is one of the most common parasites found on Macrourus species in this region.

L. szidati is part of the family Sphyriidae. Females of this species have been observed using their mouth parts to bore into the bodies of various fish and feed on their host's muscle tissue.

"These copepods are mesoparasites, meaning they are partly inside and partly outside of their host," Bernot said, adding that in the video the middle and back end of the copepods stick out of the fish, while the anterior, or head-end of their body is embedded in the fish.

Many copepod parasites have multiple stages in their life cycle and typically find their hosts while in their larval stage. These tiny larvae bury themselves within the host's skin and begin feeding. During this time they metamorphose and develop anterior holdfasts that serve as anchors to keep them attached to their hosts as they grow.

In the video, each parasite carries a pair of sacs containing hundreds of eggs. "Copepods are surprisingly good mothers for invertebrates," Bernot said. "They carry their eggs in sacs attached to their body until the eggs hatch into swimming nauplius larvae that will molt through several larval stages and eventually go on to find their own host."

Very little is known about the life cycle and lifespan of these parasites, but they are permanent fixtures to the fish and likely live for several months as they grow from a near microscopic size, Bernot said.

"Even after the parasite dies, remnants of the embedded head can still be found in their host for many years," Bernot noted.

Parasite, zombie, leech — these words are often used to describe people in unkind ways. Many of us recoil when ticks, tapeworms, fleas, head lice or bed bugs are even mentioned. Coming across such unwelcome guests — in our hair, on our skin or in our beds — can be a real nightmare.

Some parasites cause horrific deformities and diseases, maiming and killing millions of people and wildlife. Others may help boost immunity or provide the basis of food chains.

Parasites are often demonised and misunderstood. But the more we study these oddities and wonders of evolution, the more we appreciate their vital roles in ecosystems and our complex relationships with them. They're essential to life on Earth.

As an ecologist with a focus on wildlife and conservation, I wrote this article to share some of my fascination for parasites and the importance of their extraordinary lives.

Related: 32 scary parasitic diseases

What is a parasite?

Parasites rely on living organisms for food, to grow and to reproduce.

They can either live on the outside (ectoparasites) or inside (endoparasites) of their hosts. Far from being invited dinner guests, parasites typically turn up of their own accord and feed at the host's expense, consuming part or all of them.

Parasites can live within their host (or hosts) for short or extended periods — in some cases many years — going largely unnoticed. For instance, one man lived with a tapeworm in his brain for more than four years until the headaches and strange smells become too much to bear. In other cases, parasites can kill their host.

Perhaps the most gruesome type of parasite, parasitoids, kill their hosts in order to reproduce. The disturbing chest-bursting scene from the 1979 movie Alien is a truly visceral sci-fi example of a parasitoid.

In real life, examples include spider wasps that first immobilise their spider prey, lay an egg on them, and bury them. Then when the egg hatches, the wasp larvae devour the incapacitated spider. That is, of course, if another animal such as a "bin chicken (Sacred Ibis)" or insect doesn't intervene.

Parasites are typically much smaller than their hosts. Many are furnished with equipment for latching on and remaining attached, including hooks, suckers and "teeth".

Endoparasites such as tapeworms are often flat, allowing them to live within the tight spaces inside other organisms. The flatworm Diplozoon paradoxum that lives in gills of some fish must conjoin with another to reach adulthood and reproduce. Once fused, they form a permanent, lifelong bond and mate with each other over many years.

As much as 40% of all animal species may be parasites, and this mode of life might have evolved more than 200 times in the animal kingdom. But parasitism is not solely confined to animals. Many plants, fungi, protists, bacteria and viruses are parasites too.

Parasite powers

The leech scene in the iconic 1986 movie Stand By Me comes back to me every time I walk through a damp forest. The idea of providing a blood meal for another species sparks fear in many people. But leeches may also come to our aid, either by helping to reduce pooling of blood or reestablishing blood flow to areas post-surgery. Their anaesthetic saliva also has anti-inflammatory and anticoagulant properties, which are advantageous for medical procedures.

As the blood of leeches contains DNA from their past meals, conservation scientists can use them to search for rare and cryptic wildlife.

One of the world's most widespread parasites is Toxoplasma gondii. Some estimates suggest as many as one in three people are affected. This parasite's main host is cats, large and small species. House cats are frequently infected, spreading this parasite through their faeces.

While many infected people appear to have no symptoms, serious effects can include organ damage, complications with pregnancy or abortion, erratic risk-taking behaviour, mental conditions, and more traffic accidents than unaffected people.

There are potential "benefits" too. Research suggests Toxoplasma infection, which can increase confidence and risk-taking, may even be linked with increased entrepreneurial and business-related activities. Indeed, this same study found that nations with higher rates of toxoplasmosis had a lower proportion of individuals concerned about failure related to new business ventures.

Toxoplasma gondii manipulates its host to increase transmission and continue its life cycle. Infected rodents may become unwitting participants in a game of cat-and-mouse-and-parasite in which they lose their fear of cats and instead become attracted to them.

Rather than manipulating host behaviour, as in the case of fungi that turn ants into zombies, some parasites cause body malformations. This makes hosts more likely to become prey for subsequent hosts and hence to continue the parasite's life cycle. One of the most striking examples is a trematode (flatworms often known as flukes) that causes missing legs, extra legs or deformed legs in frogs and other amphibians. Extra legs, in some cases several, serve no function and simply impede movement, making it harder to escape predators.

Parasites are fundamental to ecosystems and require conservation

Parasites are a big part of life on Earth. A study on the Californian coast found the sheer mass of parasites exceeded that of top predators. In particular, the biomass of trematodes was greater than that of birds, fish, burrowing shrimps and polychaetes (marine worms).

Evidence suggests ecosystems rich in parasites are healthier than those with fewer parasites. But there is increasing concern for the survival of these species amid a growing extinction crisis. So a global plan for parasite conservation was proposed in 2020, with priorities including increased data collection and genetic analysis, making conservation assessments, and raising public awareness.

Sadly, parasites can inflict great pain, meat allergies, suffering, and a heavy death toll. Malaria, schistosomiasis (sometimes referred to as snail fever, bilharzia, and Katayama fever), and sleeping sickness are just a few examples.

But they also shape our world in profound ways, have crucial ecological roles, and paradoxically, may in some cases help keep us healthier. Though it may be confronting to admit, we need parasites as much as they need us.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

Roundworms, also known as nematodes, are a leading cause of parasitic infection worldwide, causing painful swelling, severe abdominal pain and even blindness. Now, scientists say that viruses carried by these worms may be one reason they cause such severe illness.

In a recent study, published in September in the journal Nature Microbiology, the researchers looked at more than 40 parasitic nematodes, zooming in on a molecule called RNA. A cousin of DNA, RNA helps cells make proteins and also forms the basis of various viruses.

The scientists uncovered 91 RNA viruses in 28 of the worm species studied, representing about 70% of the roundworm species that infect humans.

This study represents "the beginning of a whole other area of research on virology, pathology and more," Elodie Ghedin, a parasitologist and microbiologist at the National Institutes of Health who was not involved in the work, told Live Science.

Related: 32 scary parasitic diseases

Shannon Quek, study lead author and a parasitologist at the Liverpool School of Tropical Medicine (LSTM) in the U.K., had been studying viruses in mosquitoes, and through that work, he came up with a way to find viruses within nematodes.

Quek built an algorithm to search for signs of viruses in mosquito RNA, Mark Taylor, the senior study author and a LSTM parasitologist, told Live Science in an email. "In an inspired 'lightbulb' moment, he decided to use the same algorithm to search parasitic nematode transcriptomes," meaning readouts of all the RNA in the worms.

While mining publicly available roundworm data, the researchers looked for a marker that is seen in all RNA viruses: An RNA molecule that codes for a specific enzyme. By hunting for this marker, they identified genetic material from viruses hidden within the worms.

Only five of the more than 90 viruses the team found had been previously reported; most were newly discovered.

The team then wanted to see if there were signs of viruses multiplying in the worms. They looked at two worm species: Brugia malayi, which causes swelling of the limbs, and Onchocerca volvulus, which causes skin diseases and blindness.

In both worms, the researchers saw viruses under a microscope — specifically, they saw a virus called BMRV1 in the former and OVRV1 in the latter. In B. malayi, they saw the worm's immune defenses were raised against BMRV1. And when they mashed up B. malayi worms and studied what came out, they found viral proteins, suggesting those viruses were actively replicating.

Related: Parasitic worms infect 6 after bear meat served at family reunion

But do these viruses affect the humans that nematodes infect?

To investigate, the researchers isolated serum — blood but without clotting factors — from people who had been infected with either worm. They found antibodies against the worm-borne viruses, suggesting that people mount an immune response against them. These two viruses have only been described in the worms so far, making it unlikely that the humans could have been exposed another way.

The researchers now plan to explore whether the viruses drive any symptoms tied to these parasitic worms. O. volvulus, for example, has been implicated in onchocerciasis-associated epilepsy (OAE), a disease that leads to epileptic seizures. The worm's role in these neurological symptoms is unknown, but OVRV1 may be the culprit.

"The most likely candidate for driving disease is the rhabdovirus OVRV1," Taylor argued. Other rhabdoviruses include rabies, and broadly, they are known to infect and damage nerve cells. "This could be the elusive cause of OAE."

Some parasitic worms also harbor bacteria, like the microbe Wolbachia, which drives some of the diseases tied to roundworms.

"The system where you have a parasitic infection is not just an infection with a worm; it's that the host — the infected individual — has a worm that has bacteria, and the worm also has viruses," Ghedin said. "All of these are replicating; they're producing proteins which can make their way outside of the worm and interact with the host's immune system."

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Researchers in Mississippi have discovered a previously unknown species of parasitoid wasp that matures inside the bodies of living, adult fruit flies before bursting out of them like a xenomorph in the "Alien" movies.

The sneaky predator, which researchers have named Syntretus perlmani, is the first wasp found to infect adult fruit flies — similar wasp species are known to target flies during their younger, more vulnerable larva and pupa life stages. The wasps are parasitoids rather than parasites because they always kill their hosts, while parasites usually don't.

A team of scientists came across the wasp by chance while collecting a common fruit fly called Drosophila affinis in their backyards in Mississippi. They published their findings Wednesday (Sep. 11) in the journal Nature.

Study lead author Logan Moore, a biologist who worked on the research as part of his doctorate at Mississippi State University, told Live Science that female S. perlmani use their needle-like ovipositor organ — the stinger in stinging wasps — to stab and deposit an egg within a fruit fly's abdomen. The egg then hatches into a tiny wasp larva, which grows inside the fly for about 18 days before leaving its host for dead.

"It will effectively emerge out of the side of the fly," Moore said. "And just to add an additional layer of horror, the fly will normally remain alive for several hours after that."

Related: These bacteria trigger a sex change in wasps — scientists finally know how

The researchers were screening fruit flies for parasitic worms called nematodes in March 2023 when they first came across a spiky-tailed wasp larva inside the abdomen of one of the flies.

"At the time we didn't think it was real," Moore said. "If you dissect thousands of flies, you will see some things that are strange and odd, and you'll never see them again."

However, the scientists found more wasp larvae and eventually confirmed their discovery by rearing the wasps in a lab and studying their DNA. In the lab, mature S. perlmani larvae exited their hosts, explored for a few hours and then buried themselves in whatever substrate the researchers provided. Once undercover, they entered a cocoon stage for around 23 days before emerging as adults, according to the study.

The team paired adult wasps with other fruit flies from the genus Drosophila and found that S. perlmani was also capable of infecting Drosophila acutilabella. The researchers also discovered S. perlmani's DNA signature in publicly available genomic data of mashed-up Drosophila melanogaster, confirming the wasp infected that species as well.

Scientists have been studying Drosophila fruit flies for centuries. For example, D. melanogaster is ideal for genetic research because humans share 75% of the genes responsible for human diseases, according to the University of California, Davis. They're also easy to find, breed and study.

"Almost everybody in the world has had some sort of interaction with this fly, usually not in a good context," Moore said. "They're annoying little pests that fly around your fruit."

Finding the wasp was a surprise for the researchers because Drosophila flies are so common and well studied, which begs the question: "Why has it taken so long for this wasp to be discovered?"

"I would say maybe the one thing that would explain why it's gone undiscovered for so long is because nobody is expecting it," Moore said. "No parasitoid wasp has been known to infect the adult stage of not just Drosophila, but of flies in general."

Moore noted that the juvenile stages of insects are far more vulnerable. They aren't equipped with a thick exoskeleton like adults, and without wings, they're far less mobile.

The team still has much to learn about how this newfound species evolved to infect adults, but it seems to be very good at it. Moore and his colleagues found infected flies in Mississippi, Alabama and North Carolina, while the D. melanogaster DNA data revealed the wasp was present across the eastern United States.

"This is all around us, infecting one of the most well-studied animals on the planet," Moore said. "It just leaves you wondering what else is out there on our doormat right now."

A parasite called Toxoplasma gondii lurks inside 1 in 3 people worldwide, hiding out in the brain and other organs. Now, scientists have hijacked this microorganism to shuttle drugs into the brain — although they've yet to test the invention in humans.

Many drugs are difficult to deliver into the brain because the delicate organ is protected by a tight membrane known as the blood-brain barrier, which allows only select substances to pass out of the bloodstream and into its tissues. The barrier is especially impervious to large, water-attracting molecules, including many proteins.

Conversely, the single-celled organism T. gondii easily bypasses the brain's security — famously, when inside the brains of mice, the parasite causes rodents to forget their fear of cats. People typically pick up the parasite by swallowing it, and then it migrates to the brain on its own accord or with the co-opted help of immune cells. Most people develop no overt symptoms as a result of this, but a minority can develop disease.

In a new study, published Monday (July 29) in the journal Nature Microbiology, researchers engineered the parasite so it could carry cargo — including large proteins and packages of multiple proteins — to brain cells and then release their loads into the cells. The team demonstrated this approach in test tubes, lab mice and tiny models of the human brain known as brain organoids.

Related: 10 surprising facts about the 'mind-control' parasite Toxoplasma gondii

"This has potential implications for treatments that need to cross the blood-brain barrier," the editorial team of Nature Microbiology wrote in a research briefing about the study. Many of the study authors are now either scientific advisers to or employees of a company called Epeius Pharma, which is developing this technology for future use in human patients.

The research team got the idea to use Toxoplasma as a drug-delivery system back in 2013.

"It seemed almost too 'far out there' at the time — this parasite seems to do everything we would need to solve the problem of brain delivery," lead author Shahar Bracha, a postdoctoral associate at MIT's McGovern Institute for Brain Research, wrote in the research briefing.

Transforming the parasite into this system took years of work, during which Bracha was earning her doctorate from Tel Aviv University and collaborating closely with Lilach Sheiner, a professor of parasitology at the University of Glasgow.

"The more we explored this idea, the more feasible it seemed," Bracha said.

The experiments leveraged two structures in the parasite: the rhoptry, which injects proteins into cells from the outside, and dense granules, which secretes proteins from inside a cell.

The injection mechanism used by rhoptries — known as the kiss-and-spit — was able to deliver small amounts of proteins into targeted cells, while the dense granules delivered larger amounts of protein more successfully. The researchers suggested that, once refined, these two delivery systems might be best suited for different purposes.

When the researchers injected their engineered parasites into mice, the rodents didn't get sick. However, T. gondii isn't always harmless. In humans, especially those with weakened immune systems, the parasite can sometimes replicate out of control, damaging the brain, heart and eyes. It also poses a risk to growing fetuses and can lead to severe consequences, like blindness or brain damage.

"Unattenuated T. gondii strains still impose substantial safety risks that must be addressed," the researchers wrote in the research briefing. Moving this technology forward will require scientists to neuter the parasite, making it as harmless as possible.

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Ancient DNA recovered from human skeletons has begun to reveal the history of how malaria spread around the globe, including how the disease first reached the Americas. 

The history of humankind is outlined in stories, songs and artifacts created over tens of thousands of years. However, fewer traces remain of the pathogenic passengers that have accompanied us on this journey. Malaria is particularly mysterious because the parasitic infection causes symptoms common to a wide range of illnesses — and, when it kills, it leaves no physical marks on human bones for archaeologists to find. 

Over the past decade, though, advances in ancient DNA sampling have enabled scientists to retrieve pathogen DNA from human skeletons many thousands of years old. Traces of the pathogens that invaded a person's blood — including the parasites behind malaria — remain embedded in their bones and teeth after death, for example.

Now, these techniques have enabled researchers to investigate the epidemiology of two malaria-causing parasites: Plasmodium falciparum and Plasmodium vivax.

Related: Children can be stealth superspreaders of malaria to mosquitoes

To learn how these parasites spread around the world, researchers examined DNA from the remains of 36 people whose ages span 5,500 years and who hailed from five continents. They described their results in a study published Wednesday (June 12) in the journal Nature. By comparing the genomes of the Plasmodium parasites that infected these individuals, the researchers traced when and how malaria traveled from one region to another.

"From an evolutionary biology perspective, malaria is one of the most interesting pathogens to look at because of the profound impact it has had on the human genome," said lead author Megan Michel, a doctoral candidate at Harvard University and the Max Planck Institute for the Science of Human History in Germany. There are versions, or variants of genes involved in forming red blood cells — where malaria parasites multiply — that can offer resistance to the disease; these variants are more common among people whose ancestors lived in areas with high rates of malaria.

"Using ancient DNA allows us to go back in time and get a glimpse of what these pathogens' genomes looked like in the past and how they have evolved alongside their human hosts," Michel told Live Science.

These data could help scientists not only unravel the history of malaria but also better deal with the disease today, said Dr. Keren Landsman, a public health researcher at Augsburg University who was not involved in the study. 

"We can use this data to understand not only the pathology but also the evolutionary route of malaria — and maybe even new ways to beat it," she told Live Science. "After all, it is one of the greatest killers of our time." Malaria kills more than 600,000 people worldwide each year.

One question the researchers explored was how malaria first came to the Americas.

For answers, they turned to a person who lived high in the Peruvian Andes, at a site called Laguna de los Cóndores, about 500 years ago. Similarities between the P. vivax strain infecting that individual and other strains prevalent in Europe at the time suggest that European colonizers brought malaria to the New World. Historically, scientists have debated whether Europeans carried the parasites over or if they'd survived an earlier journey to the continent with the first Americans.

"This is exciting because it tells us how those pathogens arrived in the Americas," Michel said. "Those strains that were transmitted early in the process of colonization survived, and we found genomic evidence linking them to parasites that circulate in the region today."

Unexpectedly, the team also found evidence of malaria in colder climates. A 2,800-year-old skeleton from Chokhopani, a high-altitude site in the Himalayas, showed signs of P. falciparum infection — a puzzling finding because Chokhopani is too high, cold and dry for the mosquitoes that carry malaria to survive. 

The researchers concluded that this individual likely contracted the disease in a lower-lying region, the same way modern travelers move pathogens around the world. 

"Globalization and the movement of people are huge factors influencing malaria distribution today," Michel said. "We're moving at unprecedented rates — and we see that in reports of malaria cases imported by travelers. It's a big, big issue."

The study looked at a limited number of genomes, so it can't offer a comprehensive look at malaria's history. Someday, the researchers would like to examine more DNA samples, especially from Europe and sub-Saharan Africa. 

"I'd also love to see other pathogens that used the same routes studied in this way," Landsman said. "Understanding what else was brought by colonizers, how other pathogens spread throughout the world, and cases of immunity could help guide further research into the prevention and treatment of many diseases."

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Six family members caught a rare parasitic worm infection after sharing a meal that included black bear meat, which was initially served rare after being stored frozen for more than a month.

Two of the people reported only eating vegetables at the meal, so it's likely that the infected meat contaminated these sides at some point.

The worm infection, called trichinellosis, is rarely reported in the United States, according to a new report of the case published Thursday (May 23) by the Centers for Disease Control and Prevention (CDC). Between 2016 and 2022, only 35 probable and confirmed cases of the disease were recorded. "Bear meat was the suspected or confirmed source of infection in the majority of those outbreaks," the report noted. 

Trichinellosis occurs when people inadvertently consume larvae of a roundworm in the Trichinella genus. The worm commonly infects bears, wild boars, wildcats, foxes, wolves, seals and walruses. People typically become infected after consuming raw or undercooked meat from infected animals. 

Related: Parasitic worms found in man's brain after he likely ate undercooked bacon

Historically, people in the U.S. sometimes contracted the infection from raw or undercooked commercial pork products, but modern regulations and cooking guidelines have lowered this risk.

The newly reported case took place in 2022, when a 29-year-old man in Minnesota was hospitalized with a fever, severe muscle aches and pains and swelling around the eyes. He was also found to have a high number of immune cells called eosinophilia, a sign of infection.

Within a span of about half a month, the man had sought medical attention for his symptoms four times and was hospitalized twice. During the second hospitalization, he reported having consumed bear meat, and the medical team started him on medication for parasitic worms, just in case. They later confirmed he was carrying antibodies against Trichinella worms, and an investigation was launched to check for more cases.

About a week before he got sick, the Minnesota man had met up with nine family members in South Dakota. They'd shared a meal that included kabobs made with black bear (Ursus americanus) meat, which was originally harvested in Canada by one of the attending family members. It had been frozen for 45 days before being thawed, cooked and served with vegetables.

"The hunting outfitter had recommended freezing the meat to kill parasites," the CDC report notes. But some Trichinella species can survive being frozen. (This includes Trichinella nativa, which turned out to be the species likely involved in this case.)

"The meat was initially inadvertently served rare, reportedly because the meat was dark in color, and it was difficult for the family members to visually ascertain the level of doneness," the report noted. Some family members noticed the meat was underdone while eating it, and it was then cooked a bit more before being served again.

The affected family members hail from Arizona, Minnesota and South Dakota, and local public health officials were able to contact and interview eight of the dinner attendees. The ninth is reportedly healthy. 

Six of the eight people had developed symptoms consistent with trichinellosis. The presence of antibodies against the parasite were confirmed in two people, while the other four cases are considered "probable." Antibody testing can be tricky for this disease, because it's not super sensitive early in the course of a person's illness. All six sickened people recovered, three of whom did so after being treated in hospitals.

Samples of additional frozen bear meat from the family member's freezer were sent to the CDC for analysis, and scientists found moving Trichinella larvae in the flesh — specifically, the worms were T. nativa. The analyzed meat had been frozen for 110 days in a household freezer.

"The family member who harvested the bear and provided meat samples for testing was advised to discard any remaining meat," the report states.

Trichinellosis can cause a range of symptoms, including nausea, diarrhea, fatigue, belly pain, headache and chills. As the infection progresses, worms can migrate from the intestines into the skeletal muscles, heart muscles and nervous system, including the brain. Severe infections can cause people to have heart problems and trouble coordinating movements and breathing, sometimes leading to death.

For people cooking wild game meat, heating the meat to an internal temperature of at least 165 degrees Fahrenheit (74 degrees Celsius) will kill any Trichinella parasites. Authorities recommend confirming this temperature with a meat thermometer, as "color of meat is not a good indicator of cooking adequacy."

This article is for informational purposes only and is not meant to offer medical advice.

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Animals, as cute as some of them may be, can be a source of illness for humans. These so-called zoonotic diseases can originate from bacteria, viruses, parasites or fungi. In fact, most infectious diseases that plague people can be spread by animals. More than six in every 10 known infectious diseases in people can come from animals, while three out of every four new diseases in people originally come from animals, according to the Centers for Disease Control and Prevention(CDC). 

From rabies to fish tank granuloma, here are 32 diseases that you can catch from animals… but hopefully won't.

1. Rabies

When an infected animal bites another animal, or a person, they can transmit this nervous system ailment. Rabies takes time to pass to the brain, which is when people show symptoms like fever or headache, which progress to delirium, hallucinations and abnormal behavior. The disease is almost always fatal once symptoms appear, though it can be prevented if animals are vaccinated. In the U.S., rabies is most common in wild animals — think bats, skunks and foxes. But dogs still carry it in other countries, and they're behind most human deaths from the disease, according to the CDC. 

2. Trichinosis

Trichinosis, also known as trichinellosis, passes to humans when they eat undercooked or raw meat that carry the larvae of the roundworm Trichinella spiralis.  It particularly affects bears, cougars, wild boars and pigs, according to the CDC. Though death from trichinosis is rare, it's possible. Usually, initial symptoms include diarrhea, nausea, vomiting, stomach pain, fever and fatigue; they can progress to aching joints, itchy skin, constipation and cough. In fact, most people may pass it off as a flu. Trichinosis is diagnosed with a blood test or muscle biopsy, and prescription medications can treat it. About 20 cases a year pop up in the U.S., so it's not common but worth noting, according to the CDC.

3. Cat Scratch Disease

Your favorite feline is cute and fuzzy until they bite or scratch you — that's when you can potentially develop cat scratch disease, which is caused by the bacterium Bartonella henselae. Most people don't show any symptoms after being infected and get better without treatment. Fleas are the culprit here, as they spread the bacteria between cats. Kittens are more likely to have it than grown adult cats, and they're more likely to pass it to humans. A blood test can diagnose if you have it, and symptoms range from swollen lymph nodes to fever, headache, appetite loss and pustules near the wound. Antibiotics can help, but it usually resolves on its own — maybe unlike your relationship with the cat.

4. Ancylostoma caninum

A variety of hookworm infections can pass from dogs and cats to humans — Ancylostoma caninum is just one type. The parasite's eggs are released into the environment when an animal defecates. Animals and humans can then become infected either by inadvertently eating them or touching them with unprotected, broken skin, according to the CDC. Most hookworm infestations lead to a skin condition known as "cutaneous larva migrans," which causes redness and itching. Over time, red tracks can appear that track the larvae's movement under the skin. Itching and pain can go on for several weeks until the larvae die and the reaction clears up. Regular deworming can help eliminate the worms from pets and thus lower the chances of the parasite getting into soil nearby, hopefully ensuring you never get this parasite.

5. Bird flu

Bird flu occurs if you're infected with the avian influenza type A viruses. These viruses regularly circulate in birds and other animals, but they normally don't affect humans. Infected birds can distribute the virus via their saliva, mucus and feces. In other animals, the virus may appear in organs, blood or bodily fluids, including milk. People can acquire bird flu by getting the virus in their eyes, nose or mouth, or by inhaling it. Touching something with the virus on it and then rubbing your eyes, for example, can also put it into your body. Doctors diagnose bird flu with a nasal swab, and medications are available that can treat it, according to the CDC. Symptoms can be mild, like a flu or cold, and include fever, body aches, nausea and diarrhea. However, some cases can be severe — between January 2003 and March 2024, nearly 890 cases of human infection with a bird flu subtype called H5N1 were reported in 23 countries, and 463 were fatal.

6. Herpes B

This one's super rare, but could happen if you regularly interact with macaque monkeys. The herpes B virus can be transmitted when an infected monkey bites or scratches a person. The virus is common in these monkeys, and it can be found in their saliva, urine, feces and brain or spinal cord tissue, according to the CDC. The virus can survive for hours on surfaces, which gives it more time to spread. In humans, symptoms can start out as flu-like and then progress to muscle coordination issues and difficulty breathing. The rare infection leads to death in an estimated 70% of untreated cases. If you do come down with herpes B, antivirals are available. Just one case has been reported where someone got this and gave it to another human, so at least if it happens it's just between you and the monkey.

7. Fish tank granuloma

Fish handlers, beware. Fish tank granuloma is a rare skin infection caused by Mycobacterium marinum, an organism found in stagnant saltwater and freshwater such as ponds and aquariums, according to the American College of Osteopathic Dermatology. Handling a fish tank or shucking oysters can put you at risk for this infection. The bacteria enters through the skin, but is not spread from person to person. Your doctor may suggest a skin biopsy to confirm a diagnosis. There are antibiotics that can help, though it can take up to two years to fully clear the infection.

8. Bubonic plague

It may sound like a thing of the past, but the bubonic plague that sparked the famous Black Death epidemic still happens today. It's caused by the bacteria Yersinia pestis. Dogs, cats and rodents, such as rats and squirrels, can acquire the bacteria and spread it to humans that come in contact with their contaminated fluids or tissues. Most often, though, the microbe is transmitted to humans when they're bitten by a flea that's carrying it. Rarely, people can also get it from airborne droplets coughed out by an infected person, or by coming into contact with that person's bodily fluids. Fever, chills, weakness and swollen, painful lymph nodes are the main symptoms. Bubonic plague can still kill you if left untreated, but antibiotics can successfully cure the infection.

9. Cysticercosis

Cysts from the tapeworm Taenia solium can cause a parasitic infection known as cysticercosis. People get this by inadvertently swallowing eggs found in the feces of a person who has the tapeworm. Hand washing can help prevent its spread. Sometimes, noshing on raw or undercooked pork containing these cysts can also transmit the parasite. Blood tests can diagnose mild infections, while a magnetic resonance imaging (MRI) or computed tomography (CT) scan can be used to identify worms that have burrowed into the brain. Some people don't require treatment for cysticercosis, but it can cause symptoms such as seizures and other side effects in others, in which case medication can treat the infection. 

10. Ebola

It's thought that the Ebola virus spreads to humans through close contact with the blood, bodily fluids or organs of these primates, as well as infected monkeys, fruit bats, forest antelope and porcupines, according to the World Health Organization. Sudden fever, weakness, sore throat, headache and vomiting are initial symptoms of infection in people; impaired kidney and liver function can follow, along with both internal and external bleeding. About half of all people who contract Ebola die from it, but early care can reduce the risk of death. The good news is that we have a vaccine that works against one strain of Ebola virus, and scientists are working to develop shots for the other strains.

11. Lyme Disease

Tick bites can transmit the bacteria that causes Lyme disease. In the U.S., the bacterial culprit is typically Borrelia burgdorferi, but B. mayonii is sometimes to blame. Fever, fatigue, headache and a ring-like rash may accompany a bite. If left untreated, Lyme disease can affect your heart, joints and nervous system, and pain, fatigue or difficulty thinking can persist in Lyme patients for years. Doctors use a blood test to diagnose Lyme disease and, if you catch it early enough, antibiotics may be able to help treat the infection. The CDC estimates that about 476,000 people in the U.S. may be diagnosed with and treated for the disease each year.

12. Brucellosis

If you eat or drink unpasteurized dairy products or have an open wound, you can be at risk of Brucella infection, or brucellosis. The bacteria infect goats, cows, sheep, pigs, dogs and camels, getting into their bodies and milk. People working with the bacteria in labs are especially prone to this infection, as they can breathe in the microbe, and people who work in meat-packing plants and slaughterhouses are also vulnerable. The infection can't spread from person to person. Symptoms include malaise, anorexia, headache, depression, arthritis and fever, according to the CDC. Some symptoms can go away but others can recur. If you suspect that you have brucellosis, your doctor will conduct tests on blood, bone marrow or other body fluids. Antibiotics are available, but recovery can take a few weeks or months. The good news: death from the bacteria is rare. 

13. Mad cow disease

Also known as bovine spongiform encephalopathy (BSE), mad cow disease affects cattle and causes progressive neurological problems in the animals. BSE is caused by prions, or abnormal, pathogenic forms of proteins that can cause normal proteins near them to misfold and malfunction. Cows can develop the disease if fed meal containing tissues from affected cows, or less commonly, they can develop it spontaneously. The human form of the disease is called Creutzfeldt-Jakob disease (CJD) and people can get it by eating food products made from infected cattle. The human disease leads to rapid dementia and neuromuscular disturbances that quickly get worse. It's super rare for people to get it, but worth a mention on this list because, as of a 2020 report, no person who has contracted CJD has survived. 

14. Toxocariasis

The roundworm that causes toxocariasis can go from dogs and cats to humans, but not from human to human. Larvae from two species of Toxocara roundworms — T. canis from dogs and T. cati from cats — are shed in the animals' feces, and those eggs can be accidently swallowed by people if they touch their mouths with contaminated hands. You may not have symptoms if you pick up this parasite. That said, the infection can become systemic, in which case medications are available, while a form of the infection that affects the eyes is harder to treat, according to the CDC.

15. Echinococcosis

Echinococcosis is a parasitic disease caused by a tapeworm in the genus Echinococcus. The infection is classified either as cystic echinococcosis (CE) or alveolar echinococcosis (AE). The E. granulosus tapeworm that causes CE is found in dogs, sheep, goats and pigs. Most people that contract CE don't have symptoms but it can sometimes lead to enlarged cysts in the liver, lungs and other organs. Foxes, dogs and coyotes carry E. multilocularis, which causes AE. It's rare in humans but more serious than CE, and it can cause tumors and be fatal, according to the CDC.

16. Giardiasis

Giardia is a tiny parasite that causes the diarrheal disease giardiasis. You can pick it up from contaminated surfaces as well as from soil, food and water containing the feces of infected people or animals. The infection occurs worldwide. Some people have no symptoms while others have diarrhea, gas, greasy stools, stomach cramps, vomiting and dehydration within one to two weeks of infection, according to the CDC. Similar symptoms can emerge in pets and humans. There's a low risk of getting this parasite from your pet, but dog and cat stool can sometimes contain it. 

17. Gnathostomiasis 

Parasitic worms in the genus Gnathostoma are the culprit behind gnathostomiasis. You can get it from eating raw or undercooked fish, birds, eels, frogs and reptiles, according to the CDC. The parasite reproduces in many mammals, including dogs, cats, opossums, raccoons, pigs, tigers, leopards, wild boars and weasels. The human infection causes swelling in the skin and increases the number of eosinophils, a type of white blood cell. In rare cases, it can cause blindness. Symptoms may be non-existent at first but can progress to fatigue, fever, vomiting, stomach pain and diarrhea. Doctors diagnose it with a blood test, and there are medications to treat it. The infection is most common in Southeast Asia, but it has also affected people in South and Central America, Asia and Africa. 

18. Toxoplasmosis

Toxoplasmosis is a result of the parasite Toxoplasma gondii, also known as the cat-poop parasite. The infection can be especially serious in people who get it before or during pregnancy, and in people who are immunocompromised. Some people infected by toxoplasma don't have symptoms; others feel like they have the flu, or experience swollen lymph nodes or muscle aches lasting for a month or more. Serious cases can impact the brain, eyes and other organs. Doctors use blood tests to diagnose it; some people don't need treatment but medications are available. 

19. Swimmer's itch

The technical name for swimmer's itch is cercarial dermatitis, though some also refer to it as duck itch or clam digger's itch. It happens when people are infected by parasites in the water near ponds and lakes, and many of the parasites are found in geese, ducks and muskrats. When the animals defecate, the eggs can enter water systems and then infect shallow-water snails. The snails then release the mature parasite into the water, which puts humans at risk. If you get it, you'll see a pimple-like rash where you touched the water. The rash can start within minutes or take up to two days to appear. Swimmer's itch does typically go away on its own, but there are treatments to relieve the discomfort.

20. Crypto

Many species of Cryptosporidium can infect animals, and some can be passed on to humans. These parasites are the culprit behind the diarrheal disease cryptosporidiosis, or "Crypto." It's caused by one tough parasite whose outer shell shields it from the effects of chlorine. The parasite can spread to people in a variety of ways, but drinking contaminated water is the most common. C. parvum and C. hominis are the most common species. Immunocompromised people can be more vulnerable to the infection and have more severe symptoms, which include stomach cramps, watery diarrhea, fever, nausea and vomiting, sometimes for several weeks. Doctors diagnose Crypto with a stool sample and typically won't need to treat it, though medication is available.

21. Leptospirosis

Dogs, rodents, cattle and other wild animals can carry bacteria from the genus Leptospira, which can cause leptospirosis in animals and humans. When animals urinate, the bacteria can get into the soil or water, where they can survive for several months. If you're exposed to contaminated water, the bacteria can then get into your eyes, nose or mouth, or enter your body through broken skin. The risk of infection often increases after a hurricane or flood, which can expose people to contaminated water. Animals may not have symptoms, but humans can experience fever, muscle aches, jaundice, stomach pain and rash. Leptospirosis can cause kidney damage, meningitis, liver failure and respiratory ailments, and it can be fatal. Antibiotics can treat the infection effectively.

22. Listeriosis

Listeriosis occurs when you eat food contaminated with the bacteria Listeria monocytogenes. Listeria outbreaks are fairly common, but don't necessarily affect huge numbers of people — about 1,600 people in the U.S. get the infection each year, 260 of whom die. People who are pregnant, newborns, people with weakened immune system and older people are most likely to get it. Flu-like symptoms are common, but more-serious symptoms can include confusion, vomiting, stiff neck and seizures. An intestinal form of the illness usually doesn't need antibiotics to clear up, but an invasive illness — when the bacteria passes outside of the gut — often requires medication to cure. Pay attention to the news; if there's an outbreak, it's often widely reported in the media so people know to watch out for it.

23. Rocky Mountain spotted fever

There's a reason experts caution us to pay attention if we're in an area with ticks, and Rocky mountain spotted fever is just one of them. Get bitten by a tick carrying Rickettsia rickettsii bacteria and you could be looking at a rash, fever and headache — and if you don't get the right antibiotic in your system, the infection can be deadly. The American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni) and brown dog tick (Rhipicephalus sanguineus) can all spread Rocky Mountain spotted fever, and the illness is most commonly reported in North Carolina, Tennessee, Missouri, Arkansas and Alabama. Your doctor will do a blood test to make an official diagnosis; if you're positive, the illness can be treated with antibiotics.

24. Anthrax

You might first think of shady envelopes filled with mysterious white powders, but anthrax is actually caused by the bacteria Bacillus anthracis that can infect animals. However, it's rare to find infected animals in the U.S. People can get it by handling or consuming products from infected animals, or by breathing in spores found in animal hides, hair, wool or leather. Gastrointestinal infections can happen if you eat undercooked meat from infected animals. It doesn't spread between people. If you were to get anthrax, you'd be hospitalized and given antibiotics and antitoxin medications, as well as aggressive treatments like fluid drainage and ventilation if needed. The fatality rates differ depending on the route of exposure, but without treatment, the most fatal form — inhalation anthrax — is almost always fatal.

25. Zika virus

The Zika virus became a household name when it was spreading in the U.S. in 2015 and 2016. Mosquitoes of the genus Aedescan spread it, though it's not currently common in the U.S. The virus can pass into the womb during pregnancy, resulting in birth defects, such as microcephaly, in affected children. People can also spread Zika to one another through sexual contact. Typical symptoms include red eyes, rash, headaches, muscle pain and joint pain, although rarely, infections can affect the brain. Doctors use blood and urine tests to detect Zika virus. There aren't medications or vaccines for it, but people can treat the symptoms. 

26. E. coli

Escherichia coli, better known as E. coli, is a bacterium that normally lives in animals' and humans' intestines. It sheds when they defecate. Most strains of the bacteria won't hurt you, some can cause illness by making what's known as Shiga toxin. You can get E. coli by eating contaminated food or having direct contact with an animal or an item it's contaminated. Stomach cramping, vomiting, nausea and diarrhea can indicate that you've got the infection, which is contagious. Most people recover from the infection in about a week, although some cases can be deadly. Looking to prevent it? Cook your meats well, steer clear of unpasteurized dairy products or juice, wash raw produce and wash your hands regularly.

27. Hantavirus pulmonary syndrome

Rats and mice are the main animal reservoirs for hantaviruses, which can cause hantavirus respiratory syndrome. It most commonly occurs if you inhale dust that has been exposed to deer mice droppings, urine or saliva. Symptoms start similar to a mild flu, but your lungs can later fill with fluid and you'll have a hard time breathing as it gets worse. Most people recover, but there's no set treatment or vaccine for the virus. About one-third of all cases are fatal. Early diagnosis is key, as is access to an intensive care unit. Some people get oxygen to help them as they fight the infection. To avoid catching hantavirus, don't stir up rodent nests or other materials that have touched them, and keep rodents away from living areas. About 20 to 40 cases occur each year in the U.S., the CDC reports.

28. Psittacosis

Birds are the primary vectors for psittacosis, also known as parrot fever, and most people get sick after direct contact with a bird or inhaling dust that's contaminated with birds' feathers or feces. The disease is caused by the bacterium Chlamydophila psittaci. Cockatiels, parrots and parakeets often carry the bacteria, which can also affect other types of birds. You may not see any symptoms in the animals, though they can include poor appetite and difficulty breathing. Human symptoms of the infection include dry cough, fever, headache and muscle aches. Your doctor may do a nasal swab or test your spit or blood to confirm if you have it. Once you've got antibiotics, you should be good to go.

29. Q fever

Q fever is a bacterial disease caused by the microbe Coxiella burnetii, which infects cattle, sheep, goats and other animals. The animals may not have symptoms but can shed the bacteria in feces, urine, milk and tissues related to birth. People can get the bacteria through direct contact with an animal or its waste, and also by inhaling dust that's contaminated. Unpasteurized dairy products made from the milk of infected animals can also transmit the bacteria to humans. Symptoms of infection include cough, chills, chest pain, fatigue, headache, nausea, vomiting and diarrhea. It can lead to pneumonia or hepatitis, and, if not treated, it can be fatal. The illness can require months of treatment with antibiotics. 

30. Rat bite fever

As you can probably infer, rat-bite fever is a bacterial disease that you can get if a rat bites or scratches you. The bacterial culprits are Streptobacillus moniliformis and Spirillum minus. Expect a fever to start suddenly, followed by vomiting and headache, as well as muscle, back and joint pain. Next up, a rash develops on your hands and feet, and your joints start to swell. Mice, squirrels, dogs and cats are just a few animals that can also get the bacteria but they typically don't show symptoms. In the U.S. rat-bite fever is somewhat rare, but some people can be more prone to it than others. Left untreated, it can be fatal. That's why getting an accurate diagnosis and starting antibiotics if you do have it can be so crucial.

31. Ringworm

If your precious pet has ringworm, or dermatophytosis, you could get it too. The fungus isn't actually a worm at all. It grows on the skin of dogs, cats, rodents, rabbits, birds, cattle and other animals. You can develop an infection through direct contact with the fungus, and infections can then spread between people. Symptoms include a ring-shaped rash that may be itchy. Your doctor may diagnose an infection just by looking, or by take a scraping of your skin. Ringworm on the foot is known as athlete's foot, and it can be treated with over-the-counter medications. Non-prescription creams can typically treat the infection fairly easily, wherever it may be on the body.

32. MERS

Middle East Respiratory Syndrome (MERS) is a viral respiratory illness that’s relatively new to humans, as it was first reported in 2012. People infected with it typically develop severe respiratory illnesses that involve fever, cough, and shortness of breath. An estimated 30% to 40% of those affected die. The virus can spread to humans from infected dromedary camels (Camelus dromedarius), who likely first caught the virus from bats. People can also spread the virus to each other through close contact and respiratory droplets, if they cough. That’s why you can prevent it using normal methods you would to prevent colds. The viral infection doesn’t have a specific treatment. 

Parasitic diseases, which are passed on to people via parasites found in contaminated food, water, soil or bugs that bite humans, can be relatively uncommon in some parts of the world. In other regions, though, they can be absolutely devastating. Some parasites can cause illnesses that are temporary, but some trigger lifelong medical problems. 

Not all parasitic diseases are due to poor sanitation or poverty; you can be exposed to parasites regardless of your socioeconomic situation. Here are 32 parasites that can infect humans, including some well-known culprits and some you may not have heard of.

American trypanosomiasis

Chagas disease, also known as American trypanosomiasis, is caused by the parasite Trypanosoma cruzi. It's common in rural areas of Latin America, and its range, overall, is confined to North and South America. Insects known as kissing bugs get the parasite from an infected animal or person and then pass the parasites in their feces. Kissing bugs tend to bite their victims on the face, then defecate on the bitten person or animal. If their feces gets into the body — as might happen if you were to scratch the wound — you could get infected. Though the initial symptoms include fever, headache or rash, Chagas disease can be a lifelong illness that results in cardiac and gastrointestinal problems.

Bed bugs

Bed bugs are well-known parasitic insects that can damage furnishings with their staining poop and leave people itchy — but thankfully, these insects can't cause you lasting damage. 

Two species of the bugs, called Cimex hemipterus and Cimex lectularius, feed on humans and animals and are found across the globe. They can go months without a meal and still survive, which makes it easier for them to spread. Everyone's at risk of being bitten by bed bugs, especially if you travel. Bed bugs can cause itching, but they cannot spread disease like other parasites and don't pose a serious medical threat. You may notice their bodies in the folds of mattresses and sheets, or see rusty-colored spots from their feces. Although some people think having bed bugs indicates that a space isn't clean, that's not the case. Perhaps the biggest impact the bugs have is the costs that come with having to deep-clean areas and replace bedding, including mattresses.

Blastocystis

If you experience diarrhea, stomach pain, weight loss, itching around the anus, gas or constipation, it's possible you could be dealing with an infection caused by Blastocystis hominis. You can also carry this single-cell parasite and have no symptoms whatsoever. 

Experts aren't sure exactly how people get it — poor sanitation, eating or drinking contaminated food or water, exposure to animals or being in daycare have been flagged as risk factors for infection. It's pretty common for people to carry the parasite in their intestines, and if they develop symptoms, they can be treated with medication. That said, you'll need to submit a stool sample to get an accurate diagnosis. The good news is that the illness will often go away on its own.

Crabs (pubic lice)

You may think of crabs as a sexually transmitted infection, because they most often pass from person to person during sex. But pubic lice don't cause infections — they're parasitic insects that feed on human blood and are typically found in the genital region, though they can pop up on other coarse hairs on your body. 

Pubic lice are more common in adults, as they spread largely through sexual contact. Sometimes the bugs are visible to the naked eye, though their main symptom is itching in the genital area. Treating them is fairly simple and effective, involving special shampoos and creams. After treatment, make sure to wash any bedding, clothing or towels in hot water.

Crypto

Cryptosporidium is the parasite behind the diarrheal disease cryptosporidiosis, also called "Crypto." This parasite has an outer shell that protects it from chlorine disinfection and lets it survive for long periods of time. It can spread to people in a variety of ways, but drinking contaminated water is the most common. In fact, the parasite is the top cause of waterborne disease in people in the U.S. 

Immunocompromised people can be more vulnerable to the parasite and have more severe symptoms, including stomach cramps, watery diarrhea, fever, nausea and vomiting, which can last several weeks. Doctors diagnose Crypto with a stool sample and typically don't have to treat it, although medication is available if needed.

Dientamoeba fragilis

Dientamoeba fragilis is a parasite that infects the large intestine in humans, but it can't spread to other parts of your body. It's common around the world. Scientists aren't sure how people get D. fragilis, but suspect people typically accidentally swallow it. Some experts think that the eggs of a different parasite, called a pinworm, may help protect D. fragilis and enable it to spread.

Symptoms include diarrhea, abdominal pain, weight loss, nausea, fatigue and not feeling hungry, although not everyone develops symptoms. Doctors diagnose the infection with stool samples, and may request multiple samples over a few days. Medicines can treat it.

Diphyllobothriasis

The tapeworm Diphyllobothrium latum is the largest of its kind that can infect humans. The parasite can grow up to 30 feet (9 meters) long, and can lead to intestinal obstruction and gallbladder disease. Most people don't have any symptoms, so doctors have to take a stool sample to look for eggs from or parts of the tapeworm. If you do have symptoms, they can include stomach discomfort, diarrhea, vomiting and weight loss. You can get the tapeworm by eating undercooked or raw fish; freezing or cooking the fish will kill the parasite. Luckily, medications can treat this parasite.

Lymphatic filariasis

This parasitic disease is caused by worms that live in the human lymphatic system, part of the immune system that helps rid the body of wastes and pathogens. It's spread via the bites of several mosquito species. It can cause lymphedema, or swelling, and notably, swelling of the scrotum, called elephantiasis. 

The parasite is most common in people in subtropical and tropical areas. Doctors diagnose it with a blood test. An annual dose of medicine can help treat the infection and prevent it from spreading in communities; however, it doesn't kill all the adult worms but does kill their smaller offspring. Even if the parasite is gone, you may still have effects from it.

Giardiasis

Giardia is a tiny parasite that causes the diarrheal disease giardiasis. You can acquire it from surfaces, soil, food or water that's contaminated with the feces of infected people or animals. The infection is found worldwide. Some people have no symptoms while others have diarrhea, gas, greasy stools, stomach cramps, vomiting and dehydration within one to two weeks of infection. These symptoms can be the same in pets and humans. There's a low risk of getting this parasite from your dog or cat, though, because the type of Giardia that infects these pets is different from the type that infects humans.

Head lice

Pediculosis, commonly called head lice, is an infestation that spreads most often when people come in contact with an affected person's hair. Spread via clothing or hair brushes is uncommon. The culprit is Pediculus humanus capitis, a parasitic insect, which pets like dogs and cats can't transmit. Symptoms include tickling and itching on your scalp, and if you scratch a lot, you can develop sores. Once you're alerted that you have head lice — your doctor can probably see them with a magnifying glass — there are prescription and over-the-counter medications to kill the insects.

Hookworm

Hookworm is pretty common around the globe, but it's no longer as widespread in the U.S. The most common types of hookworm are Ancylostoma duodenale and Necator americanus. Hookworm eggs pass through human feces:if a person goes to the bathroom outdoors, the eggs can get into the soil, and the larvae can get into broken skin if you come in contact with the soil. In fact, it most commonly infects people when they walk on contaminated soil, and poor hygiene plays a factor in transmission. Some people have gastrointestinal symptoms, but many have none. You can develop anemia due to blood loss, so getting diagnosed is key; doctors collect a stool sample to confirm if you have hookworm. Medication is available to treat the parasitic worms.

Intestinal roundworms

Roundworms are a leading cause of parasitic diseases across the world, although the infections are not common in the U.S. One type of roundworm is Ascaris lumbricoides, which is often called just Ascaris and causes an infection called ascariasis. The worms' eggs pass through feces. If someone goes to the bathroom outdoors and another person's broken skin comes into contact with the contaminated dirt or they eat contaminated produce, it can spread to others. There often are not any symptoms, though they can include upset stomach or pain. Severe infections can lead to intestinal blockages or, in children, slow a kid's growth due to malnutrition. Physicians diagnose it by examining a stool sample. Medication is available to treat it.

Malaria

Also called Plasmodium infection, malaria is a disease that's caused by a parasite. Anopheles mosquitoes spread malaria from one person to another, as a mosquito can pick up the parasite if they bite a person infected with it. Symptoms of malaria include flu-like symptoms, such as fever and chills. If it's not treated, the disease can cause complications. In 2022, 249 million people across the world had malaria. Some cases are diagnosed in the U.S. each year but typically occur in people who have recently traveled to places where the disease regularly spreads.

Scabies

A mite known as Sarcoptes scabiei causes scabies. The condition occurs when the mite digs itself into the skin. That's where it lives and lays eggs. A pimple-like rash and itching are the main symptoms of the infestation, which is spread by close contact with a person who has scabies. The rash may be limited to areas like the wrist, armpit, finger webbing, genitals, waist or buttocks. You'll find scabies throughout the world, especially in crowded living spaces, such as nursing homes and prisons. The mites can live for one to two months in people's skin, which makes them hard to get rid of. Scabies can typically be diagnosed visually, and luckily, medicines called scabicides can eliminate the parasite.

Whipworm

This parasitic worm causes trichuriasis, a disease that's pretty common throughout the world, especially in warm climates with inadequate sanitation. Its eggs pass through the feces of an infected person, and it spreads to others who come into contact with contaminated soil, either by walking on it or by eating produce with the parasite on it. Some people have no symptoms; severe symptoms include painful bowel movements and rectal prolapse. A doctor can diagnose it by examining a stool sample. Medications can treat the condition.

Clonorchis

People who eat raw or undercooked fish in areas where this parasite is found — namely in Asia — can get infected with the Clonorchis parasite. The organism is known as a "liver fluke" parasite because it infects the liver, as well as the gallbladder and bile ducts. Freshwater snails eat Clonorchis eggs and release larvae that then enter freshwater fish. Most people with the parasite don't have symptoms, but when they do emerge, they can include indigestion, stomach pain, diarrhea and constipation. The infection can last for 25 to 30 years, which is how long the parasites can live in the body. Your doctor will check your stool to see if eggs are in there. The good news is there's medication that can treat it.

Pinworm

Enterobius vermicularis is a roundworm that causes what's known as pinworm infection, which is also called enterobiasis or oxyuriasis. The infection can affect anyone but it's most common in children, and those who live in close quarters. It's spread when pinworm eggs are transmitted when contaminated feces comes in contact with someone's mouth, such as via contaminated bedding, food or clothing. Sometimes the worm's eggs can spread from underneath fingernails into the mouth, if their hands come in contact with feces. Symptoms include itching around the anus. To diagnose the infection, doctors look for worms near the anus or stick tape around the anus to see if worms are there. Over-the-counter medications can treat the infection.

Keratitis

This parasitic infection is caused by the single-celled organism Acanthamoeba, a type of amoeba. It's found globally in water and soil, and it can cause infections of the eyes, skin and central nervous system, which includes the brain and spinal cord. It can enter the body through wounds or through the nostrils, and infections have also been tied to swimming with contact lenses. Blurred vision, sensitivity to light, eye pain and tearing are all symptoms of the eye infection, specifically. Eye scraping, brain scans, biopsies or spinal taps can be used to diagnose the illness. Eye infections can be tough to treat. Skin infections can be treated when they haven't spread to the central nervous system, but if the parasite gets into your brain, it can be fatal.

Toxocariasis

This roundworm infection is caused by the larvae from two species of Toxocara roundworms, called Toxocara canis, which people get from dogs, and Toxocara cati, which is from cats. It can't spread between people. Experts think a lot of humans have been exposed to the parasite because about 5% of American adults carry antibodies to it. Pets that have the parasite shed it in their feces, which can be passed to people if they don't adequately wash their hands or if they eat food contaminated with traces of dirt that contains the eggs. In rare cases, it can be passed from eating undercooked meat that contains that larvae. It can affect the eye and other organs of the body, such as the liver and lungs. However, some people with the parasite have no symptoms at all. Medications can treat the systemic infection, if it occurs, while the type that affects the eyes is harder to treat.

Schistosomiasis

Also known as bilharzia, schistosomiasis is a disease caused by parasitic worms including Schistosoma haematobium, S. japonicum and S. mansoni. People from across the globe can be affected, though the worms haven't been found in the U.S. The parasitic worms live in some types of freshwater snails. Cercariae, the larval form of the parasite, is the most infectious form and it can get from the snail into the water. People can then get schistosomiasis if they are exposed to contaminated water. A few days after exposure, you may have itching or a rash that can lead to chills, fever, cough or muscle aches within a month or two. Urine or stool samples, or a blood test, can help you get an accurate diagnosis. Medications are available to treat the parasitic infection.

Cyclosporiasis

Cyclosporiasis is an illness that affects the intestines, and it's caused by the parasite Cyclospora cayetanensis. People can get the parasite if they eat contaminated food or drink contaminated water. It's often in tropical and subtropical areas of the world. Outbreaks from food in the U.S. have been tied to imported produce. Symptoms can include loss of appetite, watery diarrhea, weight loss, stomach cramps or pain, bloating, gas, fatigue, nausea and explosive bowel movements. A stool sample is needed for diagnosis. Antibiotics can treat the infection, even though the disease isn't caused by bacteria.

Cysticercosis

The larval cysts of the tapeworm Taenia solium can cause a parasitic tissue infection known as cysticercosis. People get it when they accidentally swallow eggs in the feces of a person who has the tapeworm, which can happen if your hands aren't adequately cleaned before eating, for instance. Pigs can also get the infection if they eat tapeworm eggs. A person can't get cysticercosis from eating undercooked pork, but they could instead end up with an adult worm living in their intestines, which is known as taeniasis. Both cysticercosis and taeniasis occur globally but are most common in Africa, Asia and Latin America. Blood tests can diagnose infections, and brain scans can be used to diagnose it if it spreads to the brain. Some people don't require treatment, but medications are available for others.

Toxoplasmosis

Toxoplasmosis is a foodborne illness that's considered a leading cause of death from foodborne illnesses in the U.S. However, that said, more than 40 million people in the country carry the parasite behind the infection, called Toxoplasma gondii, which only rarely causes severe infection. Only a small percentage of people carrying the parasite have symptoms because the immune system normally overpowers it. Infection can be especially serious in people who get it before or during pregnancy and in those who are immunocompromised. Pregnant people are advised to avoid changing cat litter during their pregnancy, because the parasite is known to shed in cat feces. Some people who fall ill from the infection will feel like they have the flu or experience swollen lymph glands or muscle aches lasting for a month or more. Serious cases can impact the brain, eyes and other organs. Doctors use blood tests to diagnose it; some people don't need treatment but medications are available.

Trichomoniasis

Trichomonas vaginalis is the parasite that causes trichomoniasis, a common sexually transmitted infection that's also called "trich". Only about 30% of people develop symptoms, which include burning and itching, pain when urinating and genital discharge. Condoms can reduce the risk of spreading it. Your doctor can collect a urine or discharge sample to confirm a diagnosis. Antibiotics can easily treat the infection; not treating it will increase your risk of spreading it.

Babesiosis

Babesia microti parasites cause a disease called babesiosis and get into people when they're bitten by blacklegged ticks or deer ticks. In the U.S., where the disease is fairly rare, transmission occurs mostly in the Northeast and upper Midwest, and it gets more common during the warmer months. Flu-like symptoms can accompany infection but you may not have symptoms at all. Doctors diagnose it with blood tests and there are treatments available.

Echinococcosis

This parasitic disease is caused when a tapeworm in the genus Echinococcosis infects a human. It's either classified as cystic echinococcosis (CE) or alveolar echinococcosis (AE). The Echinococcus granulosus tapeworm that commonly causes CE is found in dogs, sheep, goats and pigs. Most people don't have symptoms when infected, but the infestation can lead to enlarged cysts in the liver, lungs and other organs. Foxes, dogs and coyotes carry Echinococcus multilocularis, which causes AE. It's rare in humans but is more serious than CE, causing parasitic tumors and sometimes fatalities.

Leishmaniasis

You'll find the Leishmania parasite in the tropics and subtropics, as well as southern parts of Europe. It causes leishmaniasis, which happens when you're bitten by a sand fly that carries the parasite. There are many different types of leishmaniasis that can affect humans; some cause skin sores while others affect organs like the liver and spleen. Your doctor may use a variety of tests to diagnose it; they may look at skin samples, bone marrow samples or blood tests. Sometimes skin sores heal on their own while sores can also occur in the nose, mouth or throat. Other times, it can be fatal.

Naegleria fowleri

Naegleria fowleri is often referred to as a "brain-eating" amoeba. It lives in soil and warm fresh water like lakes, rivers and hot springs. If water containing the parasite goes up your nose, it can get into your brain and cause an infection called primary amebic meningoencephalitis. It's super-rare — only about three people in the U.S. get it each year, on average. But the infections are almost always fatal. Symptoms are similar to having bacterial meningitis — think fever, headache, stiff neck, vomiting or confusion — which makes it harder to get a quick diagnosis.

Paragonimus

The Paragonimus lung fluke, or flatworm, can infect people's lungs if they eat raw or undercooked crab or crayfish. It's uncommon for the flatworm to travel to the central nervous system, but it sometimes can. Infection with this parasite is rare in the United States but has been reported in the Midwest. The infection is usually diagnosed by checking saliva or stool samples, though tissue biopsies aren't out of the question. Effective medications are available to treat the parasitic infection.

Anisakiasis

Parasitic worms are to blame for anisakiasis, which is also called herring worm disease. It can be caused by species of roundworms known as herringworm, codworm or sealworm. The larvae get into the water when infected marine mammals defecate, and crustaceans then eat the larvae and fish or squid eat the crustaceans. Humans can then get the parasite by eating raw or undercooked seafood. The Pseudoterranova worms invade the stomach wall and intestines in humans. Symptoms can include mild fever, nausea, stomach pain, vomiting, abdominal distention, diarrhea, and blood and mucus in the stool. Some people have allergic reactions that can, in rare cases, lead to anaphylaxis. Your doctor may use endoscopy or surgery to treat the infection by removing the worm.

Sarcocystosis

This disease is a result of the parasite Sarcocystis. It causes two types of disease in humans: the intestinal type, which causes mild fever, vomiting and diarrhea, and the muscular type, which includes muscle pain and joint pain and swelling, as well as fever. Sarcocystosis is found in tropical or subtropical countries. Eating undercooked meat containing the parasite causes the intestinal form, mostly commonly, and people who get the muscular type do so after consuming the parasite in water or food that's been contaminated with animal feces. Doctors take stool tests to diagnose the first type and tissue samples to see if you have the second form. There's no proven treatment to get rid of it, but anti-inflammatory medicines can help.

Trypanosomiasis

Also known as sleeping sickness, human African trypanosomiasis (HAT), is caused by the parasites Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense. Tsetse flies spread the disease to people. It's similar to American trypanosomiasis, or Chagas disease, in the Americas, in that they're caused by the same type of organism. HAT causes fever, headache, enlarged lymph nodes, joint pain and itching. 

The parasites can get into the central nervous system and lead to confusion, coordination problems, sleep disturbances and behavior changes. Blood and spinal fluid tests are used to diagnose the disease, and medications are available depending on the stage of the disease. In untreated cases, it almost always causes death.

A mass that had been growing in a woman's eye for two years turned out to be a parasite that sometimes passes from reptiles to humans, doctors say.

The doctors flagged contaminated crocodile meat as a potential source of the rare infection, which may make it the first case of its kind in medical literature, they reported Thursday (April 11) in  JAMA Ophthalmology.

The report's authors diagnosed the woman with an infection called "ocular pentastomiasis," a rare eye infection caused by parasites called pentastomids. In this case, a parasite had embedded itself under the conjunctiva, or clear outer membrane, of the patient's left eye. There, it had grown to about 0.4 inch (10 millimeters) long.

Related: Parasitic worms found in man's brain after he likely ate undercooked bacon

The 28-year-old, from Basankusu in Congo, showed no symptoms other than the notable mass in the corner of her eye, her doctors reported. Upon examination, they found the mass could move and surgically removed it, which revealed a pale, C-shaped larva. They shipped the grub off for further analysis, and scientists found that it belonged to a species called Armillifer grandis.

This species, along with another in the genus Armillifer, is known to sometimes cause human infections in Africa. Other types of pentastomid have been reported to infect people in other regions of the world.

Armillifer parasites use snakes as their hosts in the final stage of their life cycle, laying their eggs in the respiratory tracts of various vipers and pythons. These eggs eventually exit the lungs and enter the environment via the snake's mouth or digestive tract. There, they're picked up by a rodent or other small mammal that a snake is likely to eat; they typically develop into larvae in these hosts before getting gobbled up by a snake, thus completing the parasite's life cycle.

Humans can inadvertently pick up A. grandis by eating or drinking food or water contaminated with its eggs. or by having close contact with infected snakes, the case report authors wrote. People are sometimes exposed to the parasites through eating undercooked meat from infected snakes. In this case, though, the woman stated that she had never eaten or handled snakes.

"However, she was used to eating crocodile meat," her doctors wrote. "No case of Armillifer ocular infection has ever been reported in individuals who eat crocodile meat, but crocodiles can be infected by pentastomids." Therefore, there's a possibility the infection happened when the woman ate crocodile meat containing parasite eggs. "This meat could also have been contaminated via infected snake meat on a market stall," the doctors added.

In the rare cases when they end up in people, the parasites most often invade the internal organs and the tissues surrounding them. These infections frequently cause no symptoms, and therefore may be undercounted; they're often spotted when a person is undergoing surgery for something else. On occasion, though, these infections can lead to organ perforation, extreme immune reactions and death.

Eye infections are a rare manifestation of the disease, but they're somewhat easier to spot because they can cause symptoms of redness, pain and vision changes.

Treatment for the infection involves surgically removing the parasites. If doctors simply kill the larvae with antiparasitic drugs, the grubs' carcasses can set off a dangerous immune response in the body, the report authors wrote.

People are typically diagnosed through a visual examination of their tissues and the parasites themselves. Ways to prevent the infection include following hygiene measures, such as wearing gloves and washing hands when in contact with reptiles, as well as avoiding eating undercooked reptile meat.

The doctors say medical practitioners should be on the lookout for other cases.

"Ophthalmologists should consider the diagnosis in patients coming from endemic countries," where this rare disease is known to occur, the doctors wrote. "Higher awareness for this rare but sometimes heavily symptomatic disease seems warranted."

This article is for informational purposes only and is not meant to offer medical advice.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

A parasitic worm that infects and kills dogs has been found in California for the first time, a new study reports. The worm was discovered near the Arizona border on the banks of the Colorado River.

The discovery marks the furthest west this dog-infecting worm has been found in the U.S. The parasite, called Heterobilharzia americana, is mainly found in Gulf Coast and South Atlantic states but appears to have expanded its range into additional regions in recent years.

In dogs, the parasite causes a potentially fatal disease called canine schistosomiasis. If diagnosed promptly, the infection can be successfully treated with deworming drugs, such as praziquantel, said senior study author Adler Dillman, a professor of parasitology and chair of the department of nematology at the University of California, Riverside. The worm cannot cause schistosomiasis in humans but can sometimes irritate people's skin, causing "swimmer's itch."

Dillman and colleagues began their survey of the Colorado River, which was described March 13 in the journal Pathogens, after LA County veterinarian Dr. Emily Beeler reached out to them about a local cluster of dog illnesses. 

Related: Parasitic worms found in man's brain after he likely ate undercooked bacon 

Between 2018 and 2023, 11 dogs in three Southern California counties caught canine schistosomiasis, and one ultimately died of the infection. All had gone swimming in the Colorado River near the California-Arizona border prior to falling ill; their travel histories suggested that the river might be the common source of infection, despite H. americana not being reported in Southern California before.

"They were concerned that there might be something local," Dillman said of Beeler and her fellow veterinarians.

So Dillman and colleagues organized several trips to Blythe, a border town about an hour east of Joshua Tree National Park. The team searched for small, freshwater snails that serve as hosts for the parasite. H. americana worms infect these snails shortly after hatching, mature a bit and then get released into the surrounding water. 

The free-swimming worms then bore through the skin of a mammal host, such as a raccoon, bobcat, opossum or dog. The parasites swim through the mammal's bloodstream as they continue to mature. Eventually, they make their way to a major vein of the intestines, where they mate and lay eggs that are later shed in the animal's poop. 

However, some of the eggs end up drifting through the bloodstream and getting lodged in major organs, such as the lungs, liver or heart. There, they create hard lumps called granulomas that the immune system attacks, and if untreated, this can lead to organ dysfunction and death. 

The team collected around 2,000 snails in all, and through DNA analysis, they found that a large percentage belonged to two species known to be worm hosts: Galba humilis and Galba cubensis.

They found that a handful of the snails contained DNA from the parasitic worms — specifically, that of worms in their swimming life stage. But because only four out of hundreds of snails tested positive for this swimming stage of the parasite, it's tricky to estimate how many infected snails could be in the river overall, Dillman said. More snails in their samples may have been infected, but the worms in them may have not  yet been mature enough to be spotted in their analyses. 

"But what it does confirm for us is that they [the snails] can actually get infected in this area," he said.

Although long considered endemic to states like Florida and Texas, H. americana has more recently been found in Indiana, Tennessee, Oklahoma, Arkansas, Kansas and Utah. The new study suggests that the worm is also in California and may also be living in other Colorado River tributaries in nearby states. This warrants further investigation, Dillman said. 

In the meantime, the researchers behind the study want Calfornians to be aware of the potential risks of canine schistosomiasis and be on the lookout for its early symptoms, such as lethargy, loss of appetite, weight loss, vomiting and bloody diarrhea.

"My message is not, 'It's there, and no one should go anywhere near it,'" Dillman said. Rather, pet owners should be aware that their dog could potentially get infected by swimming in this stretch of the Colorado River near the California-Arizona border, Dillman said. 

This article is for informational purposes only and is not meant to offer medical advice.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website! 

Bedbugs have been plaguing the British for at least 1,900 years, new research reveals. Archaeologists discovered the earliest evidence of the bloodsucking parasites in the U.K. at Vindolanda, a Roman auxiliary fort just south of Hadrian's Wall in England.

Katie Wyse Jackson, a graduate student of archaeology at University College Dublin, made the discovery while investigating ancient insect remains at the fort, according to The Guardian. She found two thoraxes, the insects' midsections, at the lowest layers of Vindolanda, which was initially built in the late first century and was remodeled over the years.

The finding supports the idea that the Romans brought bedbugs (Cimex lectularius) to Britain after they invaded the isle in A.D. 43. Despite the empire's penchant for frequent bathing, evidence of bedbugs has been found at other sites in England — including a Roman settlement in Warwickshire dating to the middle to late second century — and ancient Roman sites throughout Europe. In fact, a 2016 study in the journal Parasitology found just as many bedbugs at Roman archaeological sites as in Viking and medieval ones. Considering the Romans bathed much more frequently, the finding highlights how hard it was to eliminate these pests.

"The Romans do have that reputation as being extremely clean and so it's interesting to find all of these insects that are contrary to that," Wyse Jackson told The Guardian.

Related: Smooth wooden phallus found at a Roman fort was likely a sex toy 

To look for the insects, Wyse Jackson went to Vindolanda in August 2023 and excavated several soil samples from excavation layers dating from A.D. 100 to 105. "Insects are preserved extremely well in waterlogged material," she wrote in a blog post for Vindolanda Charitable Trust. Wyse Jackson used paraffin wax, which easily sticks to insect remains in dirt, and then added water to the mix. "When the water is added, insects are more likely to float to the surface, allowing for the collection of as many insects as possible," she explained.

It's unknown how bedbugs traveled to Britain with the Romans, but one idea is that the pests hitchhiked on straw mattresses. "It's very likely they came with whatever the Romans were bringing over," Wyse Jackson told The Guardian. "The Romans were bringing over clothes, straw, grain in great quantities as they were setting up their camps," providing ample opportunity for bedbugs to join them, Wyse Jackson added.

Of course, the Romans were hardly the first to deal with bedbugs. These nocturnal, wingless insects arose around 115 million years ago during the dinosaur age, according to a 2019 study in the journal Current Biology. It's unclear what their first host was, but it was likely an animal that had a "home" where the bedbugs could hang out, like a pterosaur that laid its eggs in a nest.

You can read more about the discovery in The Guardian.

There are around 1,000 known species of parasitic fungi, which infest and feed on their insect hosts until just a shell remains. In the adapted excerpt below, from "Meetings with Remarkable Mushrooms" (The University of Chicago Press, 2023), Alison Pouliot encounters a species that targets the larvae of ghost moths, revealing how deadly fungi bring balance to the forest. 

I was in the depths of north-west Tasmania's Tarkine Forest when I spied a stick that looked suspiciously like it might not be a stick. 

Going by its size, it was probably more twig than stick, but I didn't think it was a twig either. Its slightly pointed tip and slender stature was the first clue to another identity. Running my fingers down its length I felt its fine sandpaper-like texture hinting at something non-twig. Sizing up the rather emaciated-looking thing, I reckoned it might in fact be a special type of fungus. Beneath the ground, I suspected there might be a caterpillar attached, on which the fungus fed. I carefully excavated the soil around the "twig" with my pocketknife. 

Brushing the soil away with my hand, I dug a little further and, sure enough, the perfect mummified form of a caterpillar magically materialized. This unassuming twig-like sporing body of the vegetable caterpillar is easily overlooked. Originally named Cordyceps robertsii, it was the first vegetable caterpillar fungus scientifically recorded in Australasia — in New Zealand in 1836 — and is probably one of the largest in the world. 

While many fungi parasitize plants, vegetable caterpillars seek out invertebrate hosts. Despite their common name, they don't just grow on caterpillars but on a great variety of arthropods, as well as the occasional truffle. Known as Ophiocordyceps robertsii today, this fungus usually targets moth larvae from the family Hepialidae, such as the Victorian swift moth. 

Related: Horrifying photo captures moment parasitic fungus bursts from huge spider's body

During the larval stage of their lives, caterpillars spend time mostly beneath the soil in the silk-lined shafts of their burrows. Under cover of darkness, they emerge to forage among the leaf litter. Although darkness might spare them from daytime predators, life in the litter presents multiple risks to a caterpillar, not least the chance of encountering fungus spores. Most of the millions of spores a caterpillar is likely to meet do not pose any great threat. 

Those of O. robertsii are another story. How caterpillars become infected with O. robertsii spores is a mystery. Caterpillars breathe through tiny holes called spiracles on their abdomens, so they may unintentionally inhale spores, or perhaps they brush up against spores that have already sprouted hyphae. The hyphae may then dissolve the caterpillar's cuticle (outer layer) with enzymes, allowing the fungus to penetrate its innards. 

It seems more likely that the caterpillar consumes the spores along with the organic matter on which it feeds but, whichever way the fungus finds its way into the caterpillar, it's a coup de grâce for the luckless creature. Once the fungus is inside, the caterpillar's interior provides the ideal habitat for the mycelium to proliferate. 

The fungus swiftly colonizes and liquefies the caterpillar's delicate innards via powerful enzymes that pervade the creature's entire body cavity, effectively consuming the caterpillar from the inside out. In the process, the fungus kills the caterpillar and transforms it into something resembling a fungal mummy (known as a sclerotium). 

Once satiated, the fungus sends its reproductive structure out through the head of the caterpillar and above the soil surface. It releases its spores out of tiny receptacles called perithecia (minute pores in the perithecia, called ostioles, underground lovers give it the sandpaper-like texture I felt with my hand), and they are dispersed by wind and passing animals that happen to brush against the fungus. And so the cycle begins again. 

I turned the segmented, mummified remains of the parasitized caterpillar over in my hand. I hadn't witnessed the process of its demise in the darkness of the subterrain, just the leftovers of a fungus's meal. Mulling over the caterpillar and the unassuming twig-like sporing body, I wondered how this bizarre union might play out at an ecosystem scale. Vegetable caterpillars are highly specialized fungi. 

They have evolved a swag of tricks and chemicals that enable them to manipulate the physiology and behavior of their hosts, inspiring scientists and science fiction writers alike. 

Along with other entomopathogenic fungi (those that grow in or on the bodies of insects), they play an important role in regulating populations of insects and other arthropods such as centipedes, spiders, and scorpions. Arthropods, like fungi, are vital to forest function. At times, forest conditions can change in such a way that they favor a particular species or group of arthropods. 

These changed conditions can result from local disturbances such as fire or forestry, or more global processes such as climate change. Taking advantage of the new favorable conditions, an arthropod species can multiply rapidly. The increased pressure of a population explosion on forest resources can trigger a slew of effects. These can deplete resources for other forest inhabitants, and dramatically alter forest dynamics. This is where the parasitic nature of vegetable caterpillars can do the forest a favor. 

Most species of vegetable caterpillar have limited host ranges, meaning they only associate with a small number of species. For example, one might target a particular ant genus; another might be restricted to a particular beetle genus. This specificity means they are likely to play a role in regulating arthropod population dynamics. 

By preventing any one genus or species of arthropod from gaining the upper hand, they help keep ecosystems stable. Few insect orders have been spared, with vegetable caterpillars capable of infecting the majority. Several hundred species of vegetable caterpillars have been described worldwide, occupying diverse habitats from rainforests to alpine environments and deserts. In forests they are found in soil, leaf litter, the canopy, and almost everywhere in between. 

The best-studied group of vegetable caterpillars, however, are those that parasitize ants. 

Much has been written about the so-called "zombie-ant fungi" of the O. unilateralis clade, which can modify ant behavior. This species penetrates the ant's cuticle, infiltrating its body, invading and commandeering its muscles. The ant effectively becomes a prisoner in its own body as the fungus swiftly takes the reins and compels it to climb a plant stem. Here the fungus releases chemicals that direct the contraction of the ant's jaw muscles, forcing it to latch on to the underside of a leaf. 

With its body cavity now flooded with the mycelium of the fungus, the ant dies. From this elevated vantage point, the fungus sends its spore-laden reproductive structure out through the head of the ant, raining spores on its unlucky ant allies below. 

Reprinted with permission from Meetings with Remarkable Mushrooms by Alison Pouliot, published by The University of Chicago Press. © 2023 by Alison Pouliot. All rights reserved.

Everybody poops, but only some of that poop fossilizes, turning into coprolites. While ancient droppings may sound gross — after all, who wants to go digging through feces that are centuries or even millennia old — they can offer a cornucopia of data to scientists.

For instance, coprolites can reveal which foods people ate, the parasites that lived in their guts and even prove that humans lived in an area, like North America during the last ice age, according to coprolites found in a cave in Oregon.

Here are eight times human coprolites dropped knowledge on modern scientists.

Related: 10 amazing things we learned about our human ancestors in 2022

1. Parasites galore

Human poop found in old latrines reveals that gut parasites were rampant in the ancient world. For example, biblical-era toilets in Jerusalem had excrement with protozoa that caused "traveler's diarrhea"; human waste from the Roman Empire had whipworms (Trichuris trichiura), roundworms (Ascaris lumbricoides) and Entamoeba histolytica, which can cause dysentery; and 800-year-old Crusader poop from Cyprus was teeming with whipworms and roundworms.

These unsavory hitchhikers reveal that people in these times likely ate undercooked meat, such as the uncooked and fermented fish sauce known as garum that was popular in Roman times. Or, perhaps these parasites spread through bad sanitation practices, such as contaminated water or a lack of hand washing.

2. Ancient humans in Oregon

For nearly a century, researchers thought that the first humans in the Americas were the Clovis, a group that arrived in North America shortly before 13,000 years ago. But in recent decades, researchers have found evidence indicating that humans arrived thousands of years earlier. One of those findings, of human coprolites in Oregon's Paisley Caves, shows that people were in what is now the United States by 14,500 years ago.

When the study came out in 2012, these fossilized feces were the "oldest directly dated human remains (DNA) in the Western Hemisphere," the researchers wrote in the journal Science.

3. Stonehenge-era builders ate parasite-infested meat

Neolithic construction workers left behind more than just stone structures. At Durrington Walls, a Neolithic settlement about 1.7 miles (2.8 kilometers) from Stonehenge in England, researchers found fossilized clusters of human poop, suggesting that these builders had epic winter feasts in which workers and their dogs chowed down on undercooked meat rife with the eggs of parasitic worms.

"This is the first time intestinal parasites have been recovered from Neolithic Britain, and to find them in the environment of Stonehenge is really something," study lead researcher Piers Mitchell, a biological anthropologist at the University of Cambridge in the U.K., said in a statement.

4. Disappearing high-fiber diets

The Indigenous people of the American Southwest used to eat high-fiber foods such as prickly pear, yucca and flour ground from plant seeds, according to an analysis of fossilized feces from A.D. 1150 and earlier. This diet was 20 to 30 times more fibrous than a typical modern diet, a 2012 study found. The rapid change from high-fiber to low-fiber processed foods prevalent in modern diets may explain why many Indigenous people have type 2 diabetes today.

"When we look at Native American dietary change within the 20th century, the more ancient traditions disappeared," study researcher Karl Reinhard, an environmental archaeologist at the University of Nebraska-Lincoln, previously told Live Science. "They were introduced to a whole new spectrum of foods like fry-bread, which has got a super-high glycemic index."

5. Arctic archipelago poop

Sometimes you don't find a coprolite, but the chemicals leftover from human waste. That was the case for researchers investigating periods of human occupation in the Lofoten Islands, a Norwegian archipelago in the Arctic Circle. The team took several sediment cores so they could look for chemical components of human and livestock waste. They also looked for chemical footprints of burned vegetation.

According to these chemicals, people and animals came to the area around 2,300 years ago and burned vegetation, likely to clear forests to make way for farming and grazing land. But poop output decreased around the time that Iceland was discovered, likely because people decided to migrate there. Poop levels also dropped when plague hit the region. When the Little Ice Age hit (circa 1300 to 1850), poop chemicals stayed constant while burned vegetation signatures increased, likely because settlers were stoking fires to stay warm.

6. Our Mesolithic ancestors were cannibals

In case you needed proof that Middle Stone Age, or Mesolithic humans were cannibals, look no further than their coprolites. Bits of human bones were found in human poop from 9,000 to 10,200 years ago deep in a cave in Alicante, Spain. Some bones had bite, cut and scrape marks, the researchers found. However, it's unknown if these people were eaten during rituals or because the cannibals were starving.

7. People ate cotton

Ancient DNA from 1,500-year-old coprolites in the Caribbean revealed foods favored by pre-Columbian cultures. Two groups in Puerto Rico, the Huecoid and Saladoid, used to eat an array of foods, including maize, sweet potato, chili peppers, peanuts, papaya, tomato and, unexpectedly, cotton and tobacco, according to fecal analyses. It's possible that cotton seeds or oil were consumed, but cotton oils are bitter, according to the researchers, who published their 2023 findings in the journal PLOS One. So another possibility is that Indigenous women who wove with cotton fibers used their saliva to prepare the raw yarn, the team noted.

These cultures may have also chowed down on a "variety of dietary, medicinal, and hallucinogenic plants," the researchers wrote in their 2023 study, published in the journal PLOS One.

8. Ancient hyenas ate humans

Coprolites from ancient hyenas and their bite marks on bones reveal that humans were on the menu for these carnivores up to 4,500 years ago in Saudi Arabia. The hyenas took up residence in a lava-tube cavern for several millennia, leaving behind piles of old bones, including those of humans.

It's unclear if the hyenas had killed or scavenged their human prey. Other bones in the lava tubes included those from donkeys, caprines (a type of goat), gazelles, camels and wolves or dogs.

Humpback whales have — for the first time ever — been filmed rolling to and fro on sandy seabeds to scrub off dead skin and unwanted hitchhikers.

Footage captured by researchers in the Gold Coast Bay in southeast Queensland, Australia, shows the gigantic marine mammals performing full and side "sand rolls" up to 164 feet (50 meters) below the ocean's surface to shed parasites that live on their skin, known as ectoparasites, which can make the whales less hydrodynamic.

"We believe that the whales exfoliate using the sand to assist with molting and removal of ectoparasites, such as barnacles, and specifically select areas suitable for this behavior," Olaf Meynecke, a marine ecologist at Griffith University in Australia who led the research, said in a statement.

Although humpback whales have been spotted hovering and feeding near the seafloor before, this is the first time researchers have recorded them rolling in the sand. A 2016 study published in the journal Marine Biodiversity Records suggested that humpbacks used the seabed for hygienic purposes, but the reported sightings were opportunistic and made from a boat rather than underwater.

Related: Whale sighting in Australia hints at 'extremely unusual' interspecies adoption 

Barnacles are sturdy little crustaceans related to lobsters and shrimp. They cement themselves to other sea creatures with one of the most powerful known natural glues, according to the National Oceanic and Atmospheric Administration's National Ocean Service. Whales need to remove these crusty parasites to stay streamlined and preserve energy, according to a study describing the sand rolling behavior, published March 12 in the Journal of Marine Science and Engineering.

The whales picked a shallow, sandy location near their migration route to exfoliate, moving head first through the substrate while they rolled. The density of parasites is generally higher around the face than elsewhere, so getting rid of them requires a rigorous rub, according to the study.

The researchers tagged three humpback whales (Megaptera novaeangliae) between August 2021 and October 2022 using suction-cup sensors that recorded high-definition video, as well as light, pressure, temperature and GPS data. The animals were on their summer migration path from tropical breeding grounds near the Great Barrier Reef, to cooler feeding grounds in Antarctica.

While they cannot exclude the possibility that the whales were trying to scratch off the tags, the researchers note that other individuals that were not tagged were also seen rolling across the seabed in the new footage. The tagged humpbacks also did not seem to be targeting the skin carrying the sensors.

The whale exfoliation also provided a tasty snack for small fish called silver trevally (Pseudocaranx georgianus), which were seen feeding on dead skin flakes just after the sand rolls. 

As well as staying streamlined, exfoliating on the seabed could help humpbacks maintain healthy skin. 

"Humpback whales host diverse communities of skin bacteria that can pose a threat for open wounds if bacteria grow in large numbers," Meynecke said. "Removing excess skin is likely a necessity to maintain a healthy bacterial skin community." Humpbacks remove some barnacles and skin via breaches — where a whale leaps from the water — but not all, he said.

Rolling around could also be a social activity related to play or relaxation. "During the different deployments, the sand rolling was observed in the context of socializing," Meynecke said. "The behavior was either following courtship, competition or other forms of socializing." Other whale species, including bowhead whales (Balaena mysticetus) and belugas (Delphinapterus leucas) are known to rub against rocks, pebbles and mud on the seafloor to shed excess skin. 

The parasite Toxoplasma gondii hides in up to half of humans, although it rarely causes symptoms. But when it infects mice, the single-cell organism can exert a kind of "mind control" to change the rodents' behavior and help itself spread. 

Now, researchers report being one step closer to curing T. gondii infections in humans, which can be lifelong due to the parasite's ability to morph into a dormant, defensive state. Two transcription factors — proteins that switch genes "on" and "off" — lie at the root of this metamorphosis, and the discovery opens avenues to block the process.

Often dubbed the "mind-control parasite," T. gondii takes over the minds of infected mice and steers them towards cats to become their next meal. This enables the parasites to jump into our feline friends, the only known hosts in which they can reproduce sexually. 

Scientists remain unsure whether the parasite can similarly control the human brain; some studies suggest it could contribute to aggression, impulsive behavior and schizophrenia, while other studies dispute these effects. Most people carrying T. gondii don't develop any symptoms, but more rarely, the infection can trigger mild, flu-like symptoms or even severe illness. Developing fetuses, newborns, and people with weak immune systems are most vulnerable to severe toxoplasmosis, which can damage the eyes and brain and sometimes be fatal.

Related: Can a cat parasite control your mind?

The parasite proliferates rapidly in its "tachyzoite" form. But under stressful conditions like an immune attack, T. gondii burrows into brain and muscle tissue and morphs into a "bradyzoite," which encloses itself inside a cyst and waits to revert to its active state. Immune cells and current treatments can clear away tachyzoites, but the cysts protect the bradyzoites from attack.

Parasitologist Sebastian Lourido and his colleagues at Massachusetts Institute of Technology (MIT) previously discovered a protein that switches "on" genes essential for turning tachyzoites into bradyzoites, which they named Bradyzoite-Formation Deficient 1 (BFD1). However, the regulation of BFD1 remains poorly understood. 

In the new study published April 20 in the journal Nature Microbiology, the team discovered another transcription factor that regulates BFD1, which they named BFD2. 

The study "mechanistically added a lot" to the initial story, said Mohamed-Ali Hakimi, a parasitologist at Grenoble Alpes University in France who was not involved with the work. 

When the researchers deleted the gene that codes for BFD2, they found that tachyzoites could not switch into bradyzoites and form cysts. The scientists injected 100 copies of the parasite without the gene into mice and didn't detect cysts in brain autopsies performed 45 days later. This couldn't be explained by the immune system successfully clearing away the parasite because low levels of tachyzoites were still detected.

Next, the team determined that BFD1 and BFD2 regulate each other. Stress boosted both BFD1 and BFD2 in mice, but deleting the BFD1-coding gene also silenced the gene for BFD2. The researchers determined that BFD1 binds to the BFD2-coding gene and switches it "on." 

BFD2 regulates BFD1 differently, however. When the gene for BFD2 was deleted, the BFD1-coding gene remained "on," and its genetic instructions were copied down into mRNA molecules, which are needed to synthesize the BFD1 protein. However, no protein was produced. 

The team determined that T. gondii cells maintain a supply of this mRNA, but they can only make the BFD1 protein when BFD2 binds to the mRNA and thus triggers protein synthesis. This binding only happens when the cell is under stress. 

By perpetuating each other's activity, the two transcription factors can commit tachyzoites to morphing into bradyzoites by "locking the cell into this developmental trajectory," said M. Haley Licon, parasitologist and lead author of the study. Future research could unravel what factors switch "off" this self-perpetuating loop, she added, enabling bradyzoites to revert to tachyzoites when stressful conditions elapse. 

"We still don't know what the signals that control differentiation are," Lourido told Live Science in an email. Unraveling those signals may be key to halting bradyzoite formation, he added.

"Current therapies against Toxoplasma cannot cure the infection because the chronic stages are resistant," Lourido explained. He added that inhibiting differentiation could render the parasite "susceptible to existing drugs," which could cure the infection. 

Hakimi argued that scientists are a long way from developing such drugs. "It's very hard to target transcription factors," and aside from select drugs used in cancer treatment, "very few drugs" do, he said. 

Licon agreed but is optimistic that "understanding the circuit and regulation thereof" could reveal ways to block the parasite from entering its protected, dormant state.

A tick-borne parasite has invaded new territory in the northeastern U.S. and can now be considered "endemic" in three additional states, meaning it now regularly infects people in places where it didn't before. 

The microscopic parasite, a single-celled organism called Babesia microti, can spread to humans through the bites of blacklegged ticks (Ixodes scapularis), also called deer ticks. The parasite invades red blood cells and causes an infection called babesiosis. Many babesiosis cases are asymptomatic, but some people develop flu-like symptoms, such as fever, body aches and fatigue, according to the Centers for Disease Control and Prevention (CDC). 

More rarely, babesiosis can be severe and even deadly. Those at risk of serious infections include older people, people with weakened immune systems, those with serious conditions like liver or kidney disease and those without a spleen — an immune-related organ that is sometimes removed for medical reasons. 

Between 2011 and 2019, 37 states reported 16,456 cases of babesiosis to the CDC, according to the agency's Morbidity and Mortality Weekly Report (MMWR) published March 17. More than 98% of these cases were reported by 10 states: Connecticut, Wisconsin, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, Vermont, New Hampshire and Maine. Babesiosis was already considered endemic to the first seven states prior to 2011, but not the latter three.

Related: Tick-borne illnesses are on the rise. Here's how to protect yourself. 

Over the eight-year study period, annual rates of B. microti infections skyrocketed in those last three states. Vermont's rate rose from two cases in 2011 to 34 in 2019; New Hampshire's increased from 13 to 63; and Maine's leapt from 9 to 138. 

"Based on the increasing numbers of cases, trends in rates, and the parasite's presence in ticks within the states, CDC now considers babesiosis to be endemic in these states," the MMWR authors noted.

Five other states in the "top 10" saw their annual babesiosis rates increase during the study period. These included Connecticut, Massachusetts, New Jersey, Rhode Island and New York. By contrast, the case rates in Minnesota and Wisconsin "remained stable" during this time.

"Members of the public and health care providers in states with endemic babesiosis and bordering states should be aware of the clinical signs of babesiosis and risk factors for Babesia infection," the MMWR authors concluded. 

"Persons spending time outdoors in states with endemic babesiosis should practice tick bite prevention, including wearing long pants, avoiding underbrush and long grass, and using tick repellents." 

About a decade ago, scientists observing clonal raider ants spotted something strange: Although the species is known to be queenless, a few ants were posing as queens of the colony, lording over their hardworking counterparts. These wannabe queens had wing stubs, as well as giant eyes and ovaries.

Researchers had long assumed that these "workerless social parasite" ants, which depend on other workers for survival, acquired these traits one by one, through a series of mutations. But now, scientists have discovered that a single mutation of a "supergene" can turn regular clonal raider ants (Ooceraea biroi) workers into lazy queenlike parasites.

"This was a shocking discovery," Waring "Buck" Trible, an entomologist, John Harvard Distinguished Science Fellow and the lead author of the study in which the findings were published, told Live Science in an email. "The clonal raider ant is a queenless ant species, and no winged female adults have been observed in this species previously." 

The pseudo queens are born with wings that they shed as adults, but they retain visible scars. They are the same size as worker ants, but their general indifference to labor such as brood care, foraging and nest defense makes them stand out in the colony.

Related: Mutant 'daddy shortlegs' created in a lab 

The researchers isolated the parasites and found that their offspring also had wings, suggesting that the queenlike traits were genetic. They ran analyses to confirm this observation and discovered a mutation in a "supergene" on chromosome 13.

This single mutation may be the switch that turned clonal raider ants from the "wild type" usually found in nature into a mutant variant of the same species.

"That's actually really surprising, given that the parasites differ from the wild types in so many traits, including morphology [a segmented thorax], anatomy, and even behavior," Daniel Kronauer, an associate professor and head of the Laboratory of Social Evolution and Behavior at The Rockefeller University in New York City, told Live Science in an email. 

"What we describe here is a mutant strain that is extremely closely related to its wild type ancestors. So it's not really a different species, but maybe what could be considered an intermediate form," Kronauer added.

The researchers noted that the wannabe queens laid twice as many eggs as regular clonal raider ants. They can't let their numbers grow too big, however, because they need the workers. "When they become too common they run into problems," Kronauer said. The parasites catch their bulky wings on their pupal skin when molting, and if there aren't enough workers around to help untangle them, many of them die.

The sweet spot seems to be when the parasites make up around a quarter of the colony, according to the study, published Feb. 28 in the journal Current Biology. When the wannabe queens' proportion was higher, their survival rates plummeted. 

While some species of exclusively social parasite ant queens exist in the wild, the clonal raider ant is the first documented to have evolved wannabes within its own species.

"I was very surprised to find these ants," Kronauer said. "Social parasites are typically very rare, and can only be found in a few colonies of the host species. But the crazy thing in this case is that the parasites must have arisen within the host colony via a mutation, rather than having infiltrated the colony from outside, which is the case with social parasites in the wild."

A decades-old drug for urinary tract infections may also work for "brain-eating" amoeba infections, which kill the vast majority of people who contract them, Science magazine reported.

The drug's promise was demonstrated in a recent case report, published in January in the journal Emerging Infectious Diseases, which describes a 54-year-old man whose brain was infiltrated by the amoeba Balamuthia mandrillaris. The single-celled organism lives in dust, soil and water, and can enter the body through skin wounds and cuts or through the lungs, when it's inhaled, according to the Centers for Disease Control and Prevention (CDC). The amoeba can then enter the bloodstream and travel to the brain, triggering a very rare infection called "granulomatous amebic encephalitis" that kills around 90% of people affected. 

"The disease might appear mild at first but can become more severe over weeks to several months," the CDC notes.

The man in the case report initially received treatment at a Northern California hospital for an unexplained seizure. Magnetic resonance imaging (MRI) revealed a mass on the left side of his brain, surrounded by swelling. At this point, the man was transferred to the University of California San Francisco (UCSF) Medical Center, where doctors took samples of the patient's brain tissue and the clear fluid surrounding the brain and spinal cord. This analysis revealed B. mandrillaris in the man's brain.  

Related: Boy dies from rare 'brain-eating' amoeba found in splash pad at Texas park 

After consulting the CDC, the patient's doctors prescribed an aggressive regimen of antiparasitic, antibacterial and antifungal drugs. "It's what's recommended because it was what happened to be used in patients who survived," Dr. Natasha Spottiswoode, an infectious disease physician-scientist at UCSF and first author of the case report, told Science. Unfortunately, the treatment triggered severe side effects, including kidney failure, and the patient wasn't yet amoeba-free. 

In search of another solution, Spottiswoode dug up a 2018 report, published in the journal mBio, in which UCSF scientists found evidence that an antibiotic called nitroxoline can kill B. mandrillaris in laboratory settings. The drug is approved in Europe, but not the U.S., so the medical team sought permission from the Food and Drug Administration to use it; they received approval, started the patient on nitroxoline and observed rapid improvement, within a week.

The patient was soon discharged from the hospital and he continued to take nitroxoline at home, along with other medications; his clinicians plan to eventually discontinue his use of the drugs. In the meantime, UCSF doctors are overseeing the case of a second B. mandrillaris-infected patient who's started receiving nitroxoline. They are seeing similar improvements, Science reported. 

Read more in Science.  

Toxoplasma gondii is a single-celled protozoan parasite that invades the cells of a variety of host organisms, including humans, and causes a disease known as toxoplasmosis. T. gondii is sometimes nicknamed the "mind-control parasite" because toxoplasmosis can cause a range of neurological and behavioural changes in infected animals, although most human infections have no clear symptoms.

The pathogen is one of the most common infectious parasites in the world and could lay dormant in up to half of the world's population, as well as almost any warm-blooded animal species. But there is still much we don't know about this extremely weird parasite.   

From its unusual affinity for cats to its ties to schizophrenia, here are 10 surprising facts about T. gondii.

There are many ways you can be infected with T. gondii

Humans mainly become infected with T. gondii by accidentally ingesting the parasites' eggs, or oocytes, which are excreted exclusively by cats. This can happen when people drink contaminated water, clean out litter boxes or fail to wash their hands properly after gardening or ingesting contaminated foods, such as unwashed vegetables, according to the Centers for Disease Control and Prevention (CDC). 

People can also be infected by eating the undercooked meat of other infected animals, such as pigs, sheep and shellfish, which can develop tiny, infectious cysts, or bradyzoites, after they consume oocytes from the environment, according to the CDC.

T. gondii can also be transferred from mothers to babies in the womb, as well as during organ transplants and blood transfusions, but this is much rarer, according to the CDC 

Most people have no symptoms at all 

A majority of people who become infected by T. gondii have no idea because they display no symptoms. Some people will develop mild flu-like symptoms for a few weeks as their body fights off the infection, but they normally have no long-term complications, according to the CDC.

However, pregnant women, infants and people with weakened immune systems can develop severe cases of toxoplasmosis that can cause long-term damage to the brain, eyes or other organs, according to the CDC. Occasionally, T. gondii can remain dormant in cells for years after infection before toxoplasmosis begins. 

If you think you might have toxoplasmosis then you can ask for a simple blood test from your doctor.

There is no cure for T. gondii

Doctors can treat the symptoms of toxoplasmosis using a combination of drugs such as pyrimethamine with folinic acid or sulfadiazine, according to the CDC. Although, unless a person is experiencing a severe infection or is at high risk, doctors usually don't prescribe anything to infected patients.

However, once a person has been infected with T. gondii, the parasite can lay dormant in your system for years, or even the rest of your life. At present, there is nothing doctors can do to remove the parasite, which means repeat infections are possible and therefore means there is no longlasting cure for toxoplasmosis. But it's rare for the parasite to reactivate and sicken a person later, unless the host has, or develops, a weakened immune system.

There is currently no human vaccine for T. gondii but, in the U.K., farmers can provide their sheep with lifetime protection from the parasite by using the Toxovax vaccine, according to manufacturer MSD Animal Health Hub. 

Up to half of humans are infected

Because it can be easily transmitted to humans via multiple pathways and often goes unnoticed by infected individuals, T. gondii is one of the most common infectious parasites in humans. 

A 2014 study published in journal PLOS One estimated that between 30% and 50% of the global population could be infected with or have been infected with T. gondii. But infection rates likely vary significantly in different parts of the world. For example, the CDC estimates that around 40 million Americans, or around 12% of the population, may have a T. gondii infection. But a 2020 study published in the journal Scientific Reports found that around 64% of pregnant women in Ethiopia have been infected with T. gondii at some point in their life.

T. gondii has been linked to schizophrenia and other neurological disorders

One of the parasite's most frightening — and most controversial— possible effects is its impact on the mind. In rats and other animals, it can cause behavioral changes (see more below) and it has been linked to several different neurological disorders in humans too. 

Two of the most noteworthy conditions to be linked to T. gondii are schizophrenia and bipolar disorder.

In 2006, a study published in the journal Biological Psychiatry first suggested that babies that contract T. gondii in the womb had higher rates of schizophrenia later in life than those who were not exposed prenatally. In 2014, a study published in The Journal of Nervous and Mental Disease showed that people with schizophrenia and bipolar disorder were more likely to have T. gondii antibodies in their system, which are left behind from a previous infection.

T. gondii has also been linked to changes in human behaviour, some of which could be deadly. In 2015, a study published in the Journal of Psychiatric Research suggested that T. gondii infections could make people more aggressive and impulsive, potentially even increasing the likelihood suicide. 

But the relationship between T. gondii and the brain is still unclear

Although several studies have tied T. gondii to neurological disorders, it is too early to say the parasite is directly or indirectly responsible for any of these conditions. 

Other studies, meanwhile, have called these types of links into question. 

In 2016, a study published in the journal PLOS One, which looked at more than 800 individuals born with T. gondii antibodies, found that "there was little evidence that T. gondii was related to increased risk of psychiatric disorder, poor impulse control, personality aberrations or neurocognitive impairment."

Almost all warm-blooded animals can be infected

Scientists have found traces of T. gondii infection in a wide array of different endothermic animals, including all major livestock species.

In 2005, a study published in the International Journal of Parasitology revealed that T. gondii played a role in the population decline of sea otters (Enhydra lutris) in California, with up to 38% of dead otters having been infected. Researchers suspect that agricultural run-off from contaminated soils could have introduced T. gondii oocysts to the otters' preferred food, sea kelp.

T. gondii can also pose a serious risk to penguins. In 2019, a study published in the journal Veterinary Parasitology found that around 42% of Magellanic penguins (Spheniscus magellanicus) on Magdalena Island, Chile, had been infected by T. gondii, despite the fact that the island had no cats, meaning infections were likely acquired from humans. 

T. gondii can only reproduce inside cats

Despite being found in a wide range of animals, T. gondii has only ever been observed reproducing in species from the family Felidae, which includes house cats and their wild relatives such as lions, cheetahs and tigers. House cats are believed to be the parasite's preferred host.

No one knows why T. gondii cannot reproduce inside other infected animals, but it means that cat feces is the only route that the parasite can enter the environment from. 

As of 2018, an estimated 373 million pet cats roam theEarth, according to Statistica, with possibly hundreds of millions of unregistered stray cats as well. 

Cats can only release the infectious oocytes for between one and three weeks after they become infected, after which they can no longer spread the parasites.

Birds and rodents act as intermediary hosts

Although T. gondii can only reproduce inside cats, it is also regularly found in most rodents and several bird species. 

These animals act as intermediate hosts, or a stopping off point between two different feline hosts. For example, a bird could become infected by T. gondii after eating seeds on top of dirt that had been contaminated by cat feces. That bird could then grow an infectious cyst in its body before being caught and eaten by a cat, who then becomes infected. 

As a result, rodents and birds play a key role in the success of T. gondii because they are the main way cats become infected. 

Infected rodents are more fearless

Rodents infected with T. gondii seem to lose their typical fear of cats, or more specifically, their fear of cat urine. 

A 2011 study in PLOS ONE suggested that infected rats start to feel a type of "sexual attraction" to the smell of cat urine, rather than their usual defensive response to the scent. If true, it would make infected rats more likely to live near cats, which would increase the chances of them being preyed upon. A follow-up study published in the journal PLOS Neglected Tropical Diseases in 2011 repeated the experiment in humans, but although infected men were slightly more attracted to the scent of cat urine, women were not. 

A 2020 study of mice published in the journal Cell Reports also showed that T. gondii can reduce general anxiety and increase explorative behavior in infected mice.

Live Science contributor Stephanie Bucklin contributed to this article.

Editors note: This article was updated Feb. 2 at 9:55 AM ET to correct a mistake about whether or not patients with T. gondii infections can be cured.

Toxoplasma gondii is probably the most successful parasite in the world today. This microscopic creature is capable of infecting any mammal or bird, and people across all continents are infected. Once infected, a person carries Toxoplasma for life. So far, we don't have a drug that can eradicate the parasite from the body. And there is no vaccine approved for use in humans.

Across the world, it's estimated 30–50% of people are infected with Toxoplasma — and infections may be increasing in Australia. A survey of studies conducted at blood banks and pregnancy clinics across the country in the 1970s put the infection rate at 30%. However, a recent Western Australian community-based study found 66% of people were infected.

The disease caused by this parasite can scar the back of the eye. Our new research looked for signs of disease in otherwise healthy people and found a significant number bore the mark of Toxoplasma.

We don't just get it from cats

The cat is the primary host for Toxoplasma.

Cats catch the parasite when they eat infected prey. Then, for a couple of weeks, they pass large numbers of parasites in their feces in a form that can survive for long periods in the environment, even during extreme weather.

When the feces are ingested by livestock while grazing, parasites lodge in the muscle and survive there after the animals are slaughtered for meat. Humans can become infected by eating this meat, or by eating fresh produce or drinking water soiled by cats. It is also possible for a woman infected for the first time during pregnancy to pass the infection to her unborn child.

While infection with Toxoplasma is extremely common, the most important health statistic is the rate of the disease caused by the infection, which is called toxoplasmosis.

How it affects the eye

Toxoplasma really likes the retina, the multi-layered nerve tissue that lines the eye and generates vision. Infection can cause recurring attacks of retinal inflammation and permanent retinal scarring. This is known as ocular toxoplasmosis.

Contrary to much that is written about ocular toxoplasmosis, medical research shows this condition usually affects healthy adults. However, in aged persons or people with a weakened immune system, or when contracted during pregnancy, it can be more severe.

An attack of active inflammation causes "floaters" and blurred vision. When the inflammation progresses to scarring, there may be permanent loss of vision.

In a study of patients with ocular toxoplasmosis seen at a large ophthalmology clinic, we measured reduced vision to below driving level in more than 50% of eyes, and 25% of eyes were irreversibly blind.

How many eyes?

Ophthalmologists and optometrists are quite familiar with managing ocular toxoplasmosis. But the extent of the problem is not widely recognised, even by the medical community. The number of Australians with ocular toxoplasmosis had never been measured, until now.

We wanted to investigate the prevalence of ocular toxoplasmosis in Australia, but we knew it would be challenging to get funding for a major survey of this neglected disease. So, we used information collected for a different purpose: as part of the Busselton Healthy Ageing Study, retinal photographs were taken from more than 5,000 baby boomers (born 1946–64) living in Busselton, Western Australia. The photographs were gathered to look for other eye diseases, macular degeneration and glaucoma.

By screening these retinal photographs, we estimated the prevalence of ocular toxoplasmosis at one in 150 Australians. This might seem surprisingly common, but it fits with the way people catch Toxoplasma.

In addition to pet cats, Australia has huge populations of feral cats. And Australia is home to a lot of farmland, including over 50% of the global organic farming area.

Most importantly, many Australians like to eat their red meat rare, putting them at real risk.

How the condition is treated

To diagnose ocular toxoplasmosis, a retina examination is necessary, ideally with the pupils dilated.

The retinal lesion is easy to spot, because of the way Toxoplasma activates retinal cells to produce certain proteins, and an ophthalmologist or optometrist can immediately recognise the appearance. Often a blood test is also performed to make the diagnosis.

If the condition is mild, the doctor may let the body's own immune system control the problem, which takes a few months. However, usually a combination of anti-inflammatory and anti-parasitic drugs is prescribed.

Stopping the spread

Toxoplasma infection is not curable, but it can be prevented. Meat sold in Australian supermarkets may harbor Toxoplasma. Cooking meat to an internal temperature of 66℃ or freezing it ahead of cooking are ways to kill the parasite.

Fresh fruit and vegetables should be washed before eating, and drinking untreated water (such as straight from rivers or creeks) should be avoided. Gloves should be worn when changing cat litter, and hands washed afterwards.

The World Health Organization and other international and national health bodies are promoting an approach called One Health for diseases that cross humans, animals and their environments. This involves different sectors working together to promote good health. Now we know just how common ocular toxoplasmosis is in Australia, there is real justification to harness One Health to combat Toxoplasma infections in this country.

Editor’s note: The headline of this article was changed on 5/20/2022 to reflect that the Toxoplasma parasite has not been shown to control cats’ minds. 

This article was originally published at The Conversation. See the original article here.

Dogs and cats are cute, playful, lovable… and extremely gross. Besides eating poop and licking their butts, one of the most bizarre things these pets can do is rub their rumps on the floor.

But why do dogs and cats do this "butt scooting?"

Pets rub their butts on the floor simply because it's the easiest way to itch them, said José Arce, president of the American Veterinary Medical Association. Just like humans, pets sometimes get itches on random parts of their bodies. And when a pet's butt is itchy, dragging it across the floor is the easiest way to scratch it.

Related: Why do dogs and cats run around in random bursts of speed?

Sometimes the itch and subsequent butt scoot is a one-off thing. Other times, particularly when it occurs more frequently, butt scooting can be a sign that your cat or dog is experiencing a medical issue. "It's kind of humorous; it looks like boogying or dancing. But actually, it means they're irritated," Arce said.

One trigger for butt scooting is irritated anal sacs. The anal sacs are two small glands on either side of a cat or dog's anal opening. Experts aren't entirely sure what their purpose is, Arce told Live Science, but some ideas are that the smelly fluid the glands release lubricate and scent their feces, mark territory or attract a mate. In dogs, it's relatively common for the sacs to become infected or blocked up, though less so in cats. An affected animal may butt scoot due to the irritation, potentially leaving behind feces or blood.

When fully blocked, the anal sacs can swell, and they may eventually burst. It's best to bring your pet into the vet before this happens so they can express the anal glands, clearing out the blockage — and ending the irritation and butt scooting.

Another common cause of butt scooting is intestinal parasites. Pets can't feel the parasites throughout most of their intestines, but they may be able to feel them wriggling near the anus. Any type of intestinal parasite can cause itchiness and lead to butt scooting, but Arce has found that it's especially common with hookworms and tapeworms. If a pet does have a parasitic infection, veterinarians can diagnose them with a fecal test and provide deworming treatment.

Allergies and fleas can also cause irritation that leads to butt scooting. In these cases, the pet will often also scratch other parts of their body, such as their ears. And after grooming, a dog may temporarily butt scoot because their freshly trimmed tissue is sensitive.

But butt scooting can also be a sign of a larger issue, such as a tumor of the anal sac. This is rare in cats but does occur, Arce said. It can occur in any dog breed, but is more common in spaniels.

If your dog or cat is butt scooting more than occasionally, Arce recommended taking them to the vet pronto to diagnose and treat the issue. Besides, whereas a person will likely stop scratching an itch if they begin to hurt themself, an animal may not, and they could even scoot until they ulcerate their skin.

"You might think butt scooting is humorous, but it's a sign of discomfort," Arce said. "If it repeats, see a vet, because we can diagnose the issue pretty quickly and easily."

Originally published on Live Science.

Don't sniff the fifth-century Roman flower pot. A fifth-century Roman probably pooped in it.

This is the conclusion, more or less, of a new study in which researchers analyzed the crusty build-up found inside a conical ceramic pot dating back 1,500 years. 

Once thought to be a flower pot, researchers unearthed the vessel in the bath complex of a Roman villa in Sicily, named the Villa of Gerace. But a microscopic analysis of the pot's internal crust revealed the preserved eggs of whipworm — a parasite that lives in humans’ large intestines.

According to the researchers, that means the pot must have contained human feces at one point. In other words, the flower pot is not a flower pot at all — it’s a chamber pot.

"Conical pots of this type have been recognized quite widely in the Roman Empire and in the absence of other evidence they have often been called storage jars," study co-author Roger Wilson, an archeologist at the University of British Columbia in Canada, said in a statement. "The discovery of many in or near public latrines had led to a suggestion that they might have been used as chamber pots, but until now proof has been lacking."

Measuring about 12.5 inches (32 centimeters) high and 13.5 inches (34 cm) wide at the rim, the small ceramic pot looks quite similar to the type you might pick up at a Home Depot to plant a few geraniums in. However, this portable pot would also have proven useful for bathhouse visitors who didn't want to trek to the other side of the villa when nature called. (The villa's bath complex didn’t have built-in latrines, the researchers noted.)

Given the vessel's size, it was likely used in conjunction with a wickerwork or timber chair, with the pot stashed conveniently underneath, the team said.

After many, many uses, minerals from urine and feces built up in layers inside the chamber pot, forming hard, solid concretions. If any of the pot's users happened to be infected with intestinal parasites, whipworm eggs could have gotten mixed in with those people's feces, and therefore ended up embedded in the pot's concretions, the researchers said.

"We found that the parasite eggs became entrapped within the layers of minerals that formed on the pot surface, preserving them for centuries," study co-author Sophie Rabinow, a graduate student at the University of Cambridge in the U.K., said in the statement.

This study solves the mystery of one little Roman pot, but it could also provide a framework for identifying countless other chamber pots from the era, the researchers said. The key to identifying ancient Roman potties in this manner hinges on the presence of parasite eggs — meaning at least one person infected with intestinal worms would have had to use the pot in question.

Whether or not intestinal infections were a rare occurrence in ancient Rome remains to be discovered. However, the researchers noted, in developing countries today where such infections are endemic, roughly half the population is infected by at least one type of intestinal parasite. If similar trends held in the Roman Empire, then a veritable treasure trove of chamber pots may be out there just waiting to be identified.

This study was published Feb. 11 in the Journal of Archaeological Science Reports.

Originally published on Live Science.

There's something strange in the water… a swarm of swirling, squiggling white lines, swimming from the edge of a puddle to the center and back again. They look like bolts of electricity, but they are alive. And they are getting their groove on.

These sentient squiggles are Turbatrix aceti, a species of millimeter-long, worm-like animal known as a nematode. With more than 25,000 species described so far, nematodes are some of the most prolific animals on the planet, Live Science previously reported. Many are parasites. Others, like T. aceti, feed on tiny microbes in pretty much any environment you can think of … including jars of vinegar. Hence, T. aceti's somewhat slimy nickname: the vinegar eel.

A team of scientists recently took an interest in vinegar eels not because of where the creatures live, but how they move; like many birds or fish, these unctuous creatures travel in synchronized swarms. To get a better look at the choreography of vinegar eels in motion, researchers watched colonies of thousands of vinegar eels swimming inside water droplets under a microscope. Their results were published Jan. 10 in the journal Soft Matter.

As you can see in the video of the team's experiments, that choreography is a sight to behold.

After roaming the droplet randomly for the better part of an hour, some nematodes began to cluster at the center, while others swarmed to the water's edge, racing around the rim like cars in a roundabout. Soon, individual nematodes began undulating their bodies — then, others nearby started to undulate in sync.

Before long, the entire swarm was oscillating, moving in sync to a beat only they could perceive. Lead study author Anton Peshkov, a physicist at the University of Rochester in New York, was astounded by the synchronized complexity of their movement.

"This is a combination of two different kinds of synchronization," Peshkov told ScienceNews.org. "Motion and oscillation."

One final surprise remained. As the swarm swam in unison, it pushed against the edge of the droplet, temporarily preventing the droplet from contracting as it slowly evaporated. When the team measured the force exerted by the roiling nematode horde, they found that the worms had the potential to move objects hundreds of times their own weight.

Perhaps this video can serve as a reminder that one should not underestimate the nematodes. One worm in your vinegar bottle might be an inconvenience — but a thousand worms in your bottle is a flash mob in the making. Good luck stopping that party.

Originally published on Live Science.

Researchers have discovered a new species of parasitic worm that makes its home in the mouths of tarantulas — then slowly starves the spiders to death.

The worms first appear as white splotches around a tarantula's mouth, according to a new study published Jan. 17 in The Journal of Parasitology. After being infected, the arachnid host loses control of the appendages that control its fangs, then stops eating. Infected tarantulas may also show other strange behaviors, such as walking on their tiptoes, the study authors wrote.

From there, it's a slow tiptoe toward certain death.

"It may take months because tarantulas don't have to eat particularly often," study co-author Adler Dillman, a parasitologist at the University of California, Riverside (UCR), said in a statement. "However, if they get this infection, they will die of starvation."

Dillman and his colleagues first took note of the killer worms in 2018, when a wholesale tarantula breeder reported multiple unusual deaths among his stock. Each of the affected tarantulas showed a strange white discharge around their mouths. This wasn't spider spit-up, Dillman realized right away: It was a tangled mass of parasitic worms called nematodes, living inside the spiders' fly-holes.

"Nematodes have been around for hundreds of millions of years [and] evolved to infect every kind of host on the planet including humans," Dillman said. "Any animal you know of on planet Earth, there's a nematode that can infect it."

Though more than 25,000 species of nematodes have been described to date, this is only the second species known to infect tarantulas, Dillman added. That gave his lab an exciting opportunity to get to know the elusive, spider-hunting worms.

The team learned that lab-raised nematodes were mostly hermaphrodites, meaning they produced both sperm and eggs, allowing them to self-fertilize their spawn. On average, each hermaphroditic nematode produced 160 offspring in its lifetime — which lasted about 11 days in the lab. (It's unclear how the worm's life span might change when living on a tarantula, the researchers noted.)

The researchers also learned that the nematodes only infected their hosts' mouth areas, leaving the rest of the spider untouched and unharmed.

Still, because of the newly discovered worm's spider-slaying prowess, the team gave the species a name with a bit of Hollywood cache: Tarantobelus jeffdanielsi — named for American actor Jeff Daniels.

"When I first heard a new species of nematode had been named after me, I thought, 'Why? Is there a resemblance?'" Daniels joked in a statement to UCR.

In reality, the name is an homage to Daniels' starring role in the 1990 comedy thriller "Arachnophobia," in which his character saves a small town from a deadly spider infestation.

"Honestly, I was honored by their homage to me and Arachnophobia," Daniels added. "And of course, in Hollywood, you haven't really made it until you've been recognized by those in the field of parasitology."

Originally published on Live Science.

Nature is beautiful — except when it's not. In fact, sometimes it's a little stomach-turning, or even downright horrific. In 2021, we saw plenty of examples that demonstrated just how gruesome nature could be. From sex-crazed zombies to tongue-gobbling parasites, here are some of the biggest gross-outs in science news this year. 

Mind-controlled necrophiliacs 

A type of fungus that affects house flies eats them from the inside out, consuming the flies' bodies after hijacking their brains and making them climb elevated surfaces to disperse fungal spores. Even after infected females have died, the fungus still has a use for the corpses. From inside each corpse, the fungus emits a scent that lures male flies and compels them to mate with the dead females, in order to distribute the fungal spores even more widely.

Read more: Mind-controlling fungus makes male flies mate with dead, infected females

Fuzzy eyeballs

A rare and bizarre condition affecting a male deer in Tennessee caused a dense layer of hair to sprout from its eyeballs, leaving the corneas completely covered. Known as corneal dermoids, the growths were benign tumors made up of skin tissue containing hair follicles, and they likely formed early in the animal's development. As the deer grew, what would normally have been clear corneal tissue was instead covered by a layer of skin and hair, obscuring the animal's vision. 

Read more: Why a dazed deer in Tennessee had hair growing from its eyeballs

Stomach bursters

A population of Melitaea cinxia butterflies that an ecologist released on a Finnish archipelago in 1991 introduced a Russian nesting doll set of parasites to the island ecosystem. Tucked away inside the caterpillars were the eggs and larvae of a parasitic wasp, Hyposoter horticola. And hiding inside the Hyposoter larvae was a second, smaller parasite: another wasp, Mesochorus stigmaticus. The larger wasp species hatches and grows inside the caterpillar, eventually bursting through the insect's body and killing it. But while Hyposoter grows, so too does the Mesochorus parasite, which bursts out of the living body of its wasp host and then exits the corpse of the caterpillar.

Read more: 'Russian doll' set of stomach-bursting parasites released inside butterfly on remote Finnish island

Rectal mushroom

When scientists discovered a tiny, 50 million-year-old carpenter ant preserved in amber, they noticed that the ant's body contained a little something extra: tendrils of a parasitic fungus that culminated in a bulbous cap poking from the insect's posterior. The piece of amber came from the Baltic region, and DNA analysis revealed that the fungus was a previously unknown species, which the researchers named Allocordyceps baltica. Had the insect and fungus not been engulfed by sticky tree resin and locked in an amber tomb, the mushroom that stuck out of the ant's rear-end would have released spores as part of the fungus's reproductive cycle. 

Read more: Peculiar parasitic fungi discovered growing out of the rectum of a 50 million-year-old fossilized ant

Tongue-eaters

Here's a relationship that's in questionable taste: A parasitic isopod replaced the tongue of a fish that was recently caught in Texas. Also known as a tongue-eating louse, the most well-known species of this isopod is Cymothoa exigua. Juvenile isopods swim inside a fish's mouth by entering through the gills; they then clasp onto the tongue and cut off the blood supply until the organ eventually withers and falls off. The growing isopod then replaces the tongue in the fish's mouth. But this process doesn't kill the fish, which can coexist with these parasites for years.

Read more: 'Tongue-eating' lice invade fish's mouth in this year's creepiest Halloween photo

A taste for organs

Mmmmm, organs. Asian knife-toothed kukri snakes know what they like, and what they like are frog organs, which are preferably consumed while their prey is still alive. Researchers observed multiple instances of the snakes feasting on organs from frogs in Thailand, Vietnam and Hong Kong. Kukri snakes typically use their daggerlike teeth to slice open eggs, but their teeth are equally effective when used as slashing weapons to expose frogs' innards. Two of the snakes were seen swallowing their frogs whole — but only after consuming the organs first, the scientists reported.

Read more: Snakes insert their heads into living frogs' bodies to swallow their organs (because nature is horrifying)

Social vomit

Social networks for humans might be somewhat less popular if people had to build their connections with vomit. But that system seems to work just fine for ants, which forge bonds by vomiting into each others' mouths. Known as trophallaxis, this practice allows ants to share proteins, nutrients and hormones, and it strengthens connections between colony members. An ant colony can contain thousands of individuals divided into groups, each performing specialized tasks that can affect their stomach contents. But when those contents are passed from mouth to mouth, the entire colony can share an individual's nutritional and hormonal benefits.

Read more: Ants vomit into each other's mouths to form social bonds

Caterpillar drinkers

Of course, 2021 would be the year that scientists informed us about butterflies slashing open caterpillars to drink their insides. Researchers in Indonesia watched as seven species of milkweed butterflies drank from "wounded and oozing caterpillars," in grisly meals that sometimes lasted for hours. Using tiny claws on their feet, the butterflies carved gashes in caterpillars' bodies to expose the liquid inside; because caterpillars eat milkweed plants, their body juices were brimming with chemicals from the chewed-up leaves. This made the caterpillars delicious targets for male butterflies, which use milkweed compounds to help them attract females.

Read more: Milkweed butterflies tear open caterpillars and drink them alive

Carcass shredders

It's not every day that marine biologists get to observe (and film) a group of hungry great white sharks tearing a humpback whale carcass into bite-size chunks. A team of researchers in Massachusetts embarked on a tagging mission in August and were looking for basking sharks when they spotted a shark "feeding frenzy" around the floating corpse of a young humpback in Stellwagen Bank National Marine Sanctuary. The scientists captured photos and video of the carnage and were even able to attach acoustic sensors to some of the great white sharks as they fed; that way, they could later track the movements and behaviors of these deep-sea predators.

Read more: 'Unimaginable' video shows great white sharks ripping humpback whale carcass to shreds

Butt-busting fungus

During the spring and into the summer of 2021, black-bodied, red-eyed cicadas emerged in the northeastern United States in the billions. This mass emergence happens once every 17 years, and a deadly fungus called Massospora cicadina, which only parasitizes cicadas, follows the same 17-year timetable. Fungal spores in soil cling to the exoskeleton of a cicada nymph after it digs its way out of the ground; the spores then penetrate the cicada's body and multiply as the nymph metamorphoses into an adult. Eventually, the fungus becomes so dense inside the living insect that it replaces the cicada's rear-end with a solid mass of yellow spores that are visible when that part of the cicada's exoskeleton cracks and falls off. The fungus also changes cicada behavior, making the insect mate more frequently — and thereby infect more cicadas.

Read more: Some Brood X cicadas will be sex-crazed zombies with disintegrating butts

Originally published on Live Science.

A deadly fungus infects and controls the minds of house flies, before consuming them from the inside out — and that's just the start of its gruesome reproductive strategy. As the fungus's grand finale, its spores, which poke from the cadavers of infected female flies, emit an alluring scent that seduces males into mating with the corpses. 

When the pathogenic fungus Entomophthora muscae infects house flies (Musca domestica), it begins by manipulating their behavior, compelling the flies to climb to an elevated surface, like a tall plant stem or twig. The zombie flies then cling and die there with their wings outstretched, in order to better disperse the fungal spores that sprouted from their bodies.

But for female flies, the horror doesn't end with their deaths. The fungus also emits chemicals resembling those produced by females when they're ready to mate. That sexy scent is thought to be extremely potent, because it attracts healthy males and prompts them to mount the dead females; the males in turn become infected and fly off to spread the fungal spores among their friends and neighbors.

Related: Microscopic worlds gallery: Fascinating fungi

Scientists who study this fungus and its effect on house fly hosts were previously surprised to see that healthy male flies in the laboratory were unusually interested in mating with dead, infected females, said Andreas Naundrup Hansen, a microbiology researcher at the University of Copenhagen and lead author of a new study on this previously unknown aspect of the fungal infection.

"We were very curious about this odd behavior, as it obviously seemed dangerous to the copulating male to have intimate contact with cadavers that were actively discharging infectious conidia (spores)," Hansen told Live Science in an email.

Fungal spores infect house flies by hitchhiking on a fly's exoskeleton, germinating and then breaking through the fly's tough outer cuticle. "The fungus then starts growing inside the hemocoel — the bloodstream — of the fly," absorbing nutrients from the fly's body as it grows, Hansen said. The infected fly dies about five to eight days later, and spores emerge from the dead insect approximately two hours after death. 

When the researchers tempted male flies with an assortment of female cadavers — some that were infected with the fungus and some that weren't — they found that the males more often tried to mate with infected corpses, suggesting that something related to the fungus made these particular cadavers more alluring. Analysis of chemical signatures produced by the dead females revealed a blend of several compounds that males would find irresistible, according to the study. 

Simply irresistible

Two of the compounds found in the aromas of these dead flies were ethyl octanoate and a group of chemicals known as sesquiterpenes, both of which are known for their insect-luring abilities. Though spores emerged from the females' bodies just a few hours after the insects died, the corpses were at their most attractive to males during the later stages of spore production: approximately 25 to 30 hours after death.

Other species of pathogenic fungi also use chemicals to alter the behavior of their insect hosts. Fungi from the genus Massospora infuse the nervous systems of cicadas with mind-altering psilocin and cathinone — the active compounds in hallucinogenic mushrooms — turning cicadas into sex-crazed zombies that spread the pathogen as they mate with as many partners as possible, Live Science previously reported. 

Another mind-bending example, the fungus Ophiocordyceps unilateralis, infects carpenter ants in the genus Camponotus using two compounds, guanidinobutyric acid and sphingosine, which are also thought to affect behavior, Hansen said. Once this fungus takes control of an ant's brain and nervous system, it leads the ant on a death march up a plant stem or to the top of a shrub or bush. There, the insect clamps its mandibles into the plant and hangs on until it dies; the fungus then releases its spores to infect more ants.

One possible explanation for E. muscae's combination of behavior manipulation and sexual mimicry is that attracting male house fly hosts could be especially important for the fungus because it's a species-specific pathogen that infects only house flies, the researchers suggested. 

"When the access to new hosts are limited, it's crucial for the fungus to ensure transmission to new suitable hosts of the right species," Hansen said.

The findings were published Oct. 22 on the preprint server bioRxiv and have not been peer reviewed.

Originally published on Live Science.

In any relationship, there's usually one partner that does the heavy lifting.

In the case of one alien-looking parasitic isopod, that's the female, who has the tough job of gobbling up a fish's tongue and replacing it with her own body. The male, meanwhile, takes the easy route and simply hangs out in a fish's gills, eating mucus all day.

A recent photo captured this disturbing parasitic relationship in the mouth of an Atlantic croaker (Micropogonias undulatus) caught in Galveston Island State Park in Texas. The fish's tongue had been completely replaced by this so-called tongue-eating louse.

Though unsettling, such parasitic encounters are far from rare. These creepy creatures routinely feed on fish in warm waters worldwide, including the Gulf of Mexico, as several commenters noted on Galveston Island State Park's Facebook post. As members of the order Isopoda, they are nightmarish cousins of the roly-poly pill bugs found in many backyards, Mark Fisher, science director at the Texas Parks and Wildlife Department, told Texas news outlet KSAT.

Related: 8 awful parasite infections that will make your skin crawl

There are several species of tongue-eating lice, the most well-known of which (Cymothoa exigua) inspired the 2012 horror flick The Bay, according to AAAS. Many species target one particular type of fish, the same way tropical moths have evolved to feed on specific orchids, according to research published in 2014 in the International Journal for Parasitology. Fisher told members of the press that he had never seen one in an Atlantic croaker before, NPR reported. 

When a group of juvenile isopods finds a fish, the critters swim into the fish's gills and latch on with their spiky, clawed legs. At this point in their life cycle, all of the isopods are male — but one louse will grow larger than the rest, make its way into the fish's mouth and become female. There, she will attach herself to the blood vessels at the base of the tongue and feed until the tongue rots away. 

Fortunately, the parasites have no interest in human tongues. And despite the ick factor, they don't seem to substantially harm the fish they call home, according to PBS' NOVA. Instead, the fish simply uses its parasite like a prosthetic tongue, and fish can live with these parasitic interlopers for years, Live Science previously reported. Meanwhile, the female isopod continues to chow down on its host's blood and mouth mucus, while the males stay in the gills, occasionally sneaking into the fish's mouth to mate with its new faux tongue. 

So, if you're looking for a fright this Halloween, consider fishing. "It can be a surprise to peer into a fish's mouth and have another set of eyes looking back at you," Fisher said.

Originally published on Live Science.

A prizewinning microscopy image of a tick's head rendered in psychedelic colors may change the way you look at bloodsucking parasites.

The intense magnification — combined with glowing hues that illuminate the creature's protruding head, internal structures and armored, spiky exoskeleton — make the tick seem more like a bizarre (or beautiful?) visitor from another world. 

The image offers a perspective of the tiny arthropod that you've probably never seen before. And that's exactly the point of this and other standout entries that were recently honored in the Nikon Small World Photomicrography Competition, now in its 47th year. The tick photo, and more than 100 others chosen for the contest's top awards, showcase the science and beauty of organisms, minerals and other objects that are too small to be seen with the naked eye.

Related: Magnificent microphotography: 50 tiny wonders

However, for a microscopy image to really stand out from the pack, it's not enough for it to just look beautiful, said contest judge Alexa L. Mattheyses, an associate professor at the University of Alabama at Birmingham’s School of Medicine. 

Instead, an image also has to trigger your curiosity. "Does it spark something in you; do you want to know more about it?" Mattheyses told Live Science. "The subject matter is so diverse; that's where having a diverse panel of judges comes into play, because we're all drawn to different things," Mattheyses said. 

On one level, judging the photos required looking at them "like any other kind of art," said contest judge Hank Green, a YouTube content creator, author and science communicator.

"We talked about how the images made us feel, their composition, the stories they told, the techniques that were used," Green told Live Science in an email. "There was special attention paid to things that anyone could enjoy, but that enjoyment would get deeper when you understood it more deeply."

For the contest, five judges evaluated nearly 1,900 submissions from 88 countries, awarding the tick image seventh place overall. It was captured by researchers Paul Stoodley, director of Ohio State University's Campus Microscopy and Imaging Facility (CMIF), and Tong Zhang, CMIF's associate director and senior microscopist, using confocal microscopy, which focuses laser light on a subject while a pinhole lets in a very small amount of light and blocks the parts of the image that are out of focus. 

"People can see some fine details in this tick head, and especially its mouth region with [an] inverted-arrow-like structure. Ticks use this kind of structure to anchor them on animals," Zhang told Live Science in an email. The image's color scheme made the mouth region stand out from the rest of the head, he said.

The competition's first place award went to Jason Kirk, technical director of the Optical Imaging and Vital Microscopy Core at Baylor College of Medicine in Houston, Texas, for his image of the underside of an oak leaf and its delicate, protective structures called trichomes. The photo shows the leaf's white trichomes nestled among pink pores, where they resemble tentacled sea anemones.

"This photograph is really the result of an experimental microscope system that I was building at home," Kirk told Live Science. When Kirk's daughter brought in an oak leaf to test the equipment, he was intrigued by the trichomes on the leaf's underside. For the contest photo, Kirk collected newly sprouted oak leaves in which the trichomes were just starting to emerge. 

"The biggest technical challenge was lighting," he said. Illuminating the tiny structures required delicately balancing the color and temperature of three light sources: one on top of the leaf, one underneath and one on the side that lit up the trichomes.

The oak leaf "was something that was in our backyard and something that we interact with every day, but you don't really have an appreciation for what it really looks like up close," he said. "I hope that it makes people look a little bit harder at the things that are right under their feet."

"Being able to see all the beautiful images that scientists as well as amateur scientists took and submitted, it does open your mind up to different ways to acquire images, and different types of information you can get out of them," Mattheyses said. "I found it really inspiring and energizing to be able to do that judging, and then go back to my own work and see some new stuff!"

For those of us who don't regularly peer through microscopes at tiny wonders, seeing these images can still be a transformative experience, Green said.

"I think the more time you spend in the microcosmos, the better your appreciation for everything," he said. "If you pay enough attention it can take you from, 'Why doesn't anything work in this broken world?' to 'It's so awe-inspiring that anything works at all.'"

You can see all of the contest's top 20 winners and honorable mentions on the Nikon Small World website.

Originally published on Live Science.

A fungus that resembles decaying human fingers is endangered but hanging on for dear life in Australia, wrapping its zombie-like digits around fallen trees on an island near the continent's southern coast.

Hypocreopsis amplectens is commonly known as tea-tree fingers, as its shape resembles pudgy human fingers clinging to wood on the forest floor, though the mottled pinkish-brown color and texture of the fungus make those fingers look more dead than alive. 

Tea-tree fingers are extremely rare, known to exist in just a handful of locations on the mainland of Victoria in southeastern Australia. But an expedition led by naturalists from Australia's Royal Botanic Gardens Victoria (RBGV) recently proved that the fungus has tightened its grip in at least two other places in the Australian state.

Related: Microscopic worlds gallery: Fascinating fungi 

The fungus' fleshy appearance may be ghastly to humans, but it evolved into that bizarre shape to help it survive, said Michael Amor, a postdoctoral fellow at RBGV and a leader of the fungus-finding expedition.

"As it is found on dead, often disconnected branches, the finger-like form may help it be flexible enough to grow over curves/crevices and cope with bending, cracking and falling," Amor told Live Science in an email.

The fungus is a parasite, growing on another fungus host that decays wood. It's also a tasty snack for moth larvae and other insects, "so it is an example of the complex food-webs that characterise intact ecosystems," Amor said.

A team of researchers and volunteers reported finding tea-tree fingers in two locations at a protected national park on French Island, Victoria, according to an RBGV statement. One of those spots holds the largest recorded population of tea-tree fingers — over 100 individual fruiting bodies, more than the total fungus population at all the sites on the mainland.

Finding so many examples of these dead-looking digits offers hope for the parasite's future, as a warming climate and habitat loss are causing the fungus to lose its grip on the mainland, according to the statement.

"Tea-tree fingers is a highly specialised fungus that requires a particular set of conditions to grow. It needs specific tree species to occur at just the right density to provide ideal humidity and canopy cover," Amor explained in the email. "Large areas of natural vegetation are required to allow for these precise micro-climates to occur and, sadly, we are losing these at an alarming rate."  

Amor is using DNA analysis to see if habitat fragmentation and isolation of the fungus populations has affected their genetic health. Other ecologists are investigating the delicate balance of organisms in the fungus' ecosystems, to pinpoint the conditions that allow the fungus to thrive.

Meanwhile, the dead-finger fungus will just keep doing what it does best: hanging in there.

Originally published on Live Science.

Stomach-bursting eels! Tongue-devouring sea lice! Nature can be the best at being the absolute worst, and 2020 gifted us with a petrifying parade of shudder-inducing science. From baby-eating cannibal monkeys to vampire parasites, here are 10 times this year when nature proved that it was positively horrific. You're welcome.

Bone-eaters

Scavengers in the deep ocean eagerly devour alligator corpses — some pick the bones clean, while others munch on the bones, scientists recently discovered. Researchers sent three dead freshwater gators to the sea bottom in the Gulf of Mexico, depositing them at a depth of 6,600 feet (2 kilometers) to see how marine creatures might respond to a type of food that they wouldn't usually find on the sea floor. Turns out those deep sea critters aren't picky.

Footage captured by a camera on a diving robot showed that enormous pink isopods (crustaceans that resemble terrestrial woodlice or pill bugs, at a much larger scale) swarmed over the alligators, stripping flesh from the skeletons. After all the meat was gone, the bones were covered in a brown fuzz, and DNA analysis revealed that this coating was a previously unknown species of bone-eating worm.

Read more: New bone-eating life form discovered in bizarre alligator-corpse study

Toxic toupeé

What looks like a walking wig, except with "hairs" that are really venom-spurting spines? It's the caterpillar of the southern flannel moth (Megalopyge opercularis), and these toxic "toupeés" appeared in Virginia in record numbers this year. As climate change warms the planet, animals shift their ranges in response, and global warming could explain why the caterpillars were more numerous in Virginia in 2020 than they usually are. 

Read more: Weird venomous caterpillars that look like walking toupées are invading Virginia

Hornets from hell

Asian giant hornets (Vespa mandarinia), the biggest hornets in the world, are gaining a foothold in the United States for the first time; the size of their stingers and the potency of their venom makes the insects uniquely dangerous to people, but the hornets pose a much greater threat to North American honeybees. 

Researchers in Washington first found individual hornets — also known as murder hornets — in April. The first murder hornet nest was found and destroyed in October, and that nest may have held as many as 200 new queens. Hornet queens can grow to be 2 inches (5 centimeters) in length, and female workers and males measure about 1 to 1.5 inches (3.5 to 3.9 cm), and they are known for mobbing honey bees' hives, killing or driving off all the bees, and then moving in and taking over the abandoned nurseries, feeding the bee larvae to their hornet babies.

Read more: Monstrous 'murder hornets' have reached the US

'Vampire' parasite

It was just another Monday for biologist Kory Evans, an assistant professor in the Department of BioSciences at Rice University in Houston, Texas, when he X-rayed a fish's head in 3D and discovered that its tongue had been replaced by a parasite. 

Actually, his Mondays "aren't usually this eventful," Evans wrote on Twitter.

Instead of a normal tongue, the fish had a tongue-eating isopod squatting inside its mouth. These so-called vampire crustaceans enter a fish's mouth as larvae, attach to the tongue by tightly gripping it with their legs, and feed on blood that they siphon from the organ. Eventually, the tongue withers and falls off, and the now-fully-grown isopod serves as a functional tongue for the fish. 

Read more: Meet the 'vampire' parasite that masquerades as a living tongue

Gone fishing

A sizable semi-aquatic spider went fishing and snagged a man's pet goldfish, named Cleo, out of a backyard pond in Barberton, South Africa. The man arrived home just in time to capture photos of the heinous act, as the arachnid — a nursery web spider, also known as a fishing spider — dragged poor Cleo from the water. Cleo was likely already dead at this point, killed by a venomous bite. And though she was about twice the size of her attacker, these spiders can easily subdue prey up to five times their size, scientists reported in 2014.

Read more: A man caught a spider eating his pet goldfish and, well, it's terrifying

Embryo infection

In case you're wondering what it might take to shock a scientist; researchers in Sweden were dissecting developing lizard embryos, when they were extremely surprised to see "something moving" in the brains of the embryonic lizards. The scientists found that nematodes, a type of parasitic worm, had infested the ovaries in the embryos' mothers. From there, the parasites were able to pass into the embryos' brains before the hard shell of an egg could form around them, so the baby lizards were already parasitized when they hatched.

Read more: 'Shocked' scientists find brain parasites in baby lizards still in shells

Loon vs. eagle

When a dead eagle was found with a puncture in its chest, experts determined that the murder weapon was likely the "dagger-like bill" of a loon. A game warden in Maine found the eagle's body near a lake and brought it to a nearby veterinarian, thinking that the bird had been shot. A radiograph showed that there was no bullet in the body, but there was a deep wound that was similar in size to a loon's beak. The eagle was found with a dead loon chick nearby, and scientists suspect that a loon parent tried to defend its baby from the attacking eagle, landing a lethal jab that pierced the predator's heart. 

Read more: Loon stabs bald eagle to death

Stomach-burster: fish edition

When fish gulp down sinuous snake eels, the eels can stage a desperate escape by using a hardened, bony tail tip to punch a hole in the predator's gut. But that strategy might leave a swallowed eel in an even worse predicament: once it slips out of the stomach, it's still trapped inside the bigger fish's gut cavity. Scientists recently documented grisly evidence of such failed escapes, finding mummified snake eels inside the bodies of more than a dozen predatory Protonibea diacanthus fish in waters around coastal Australia.

Read more: Snake eels stage stomach-bursting escape after being eaten (and then things get really nasty)

Stomach-burster: bird edition

As if one gruesome stomach-burster story wasn't enough, 2020 decided that we needed another. In this case, the predator was a heron in Delaware that swallowed an American eel (Anguilla rostrata). But the eel had other plans, and photographer Sam Davis of Maryland captured the incredible sight of the heron in flight, with the eel emerging headfirst from the bird's stomach, bursting all the way out of the bird's body to dangle in midair under the heron's outstretched neck.

"I could see the eel, you could see its eyes," Davis told Live Science.

Read more: Alien-like photo shows eel dangling out of heron's stomach in midair

Capuchin cannibals

Scientists reported the first known case of infant cannibalism practiced by white-faced capuchin monkeys (Cebus imitator), in a population that researchers have observed for nearly four decades in Costa Rica's Santa Rosa National Park. After a 10-day-old baby monkey fell from a tree, possibly killed by an older male, two monkeys from the troop partly consumed the dead infant while its mother watched nearby. Cannibalism in monkeys from Central and South America is exceptionally rare, and typically happens when infants are killed by unrelated monkeys, with the baby's relatives eating the remains.

Read more: Adorable monkeys caught committing grisly act of cannibalism

Originally published on Live Science.

There's a single-celled parasite called Toxoplasma gondii, and it can turn a normally risk-averse mouse into a bold, cat-seeking rodent. Cats that devour such mice can then pass the parasite onto humans.

But once humans are infected, what happens to them? Do they become Toxoplasma gondii zombies, acting however the parasite deems fit?

The answer is complex; studies show that people who test positive for this condition are more likely to take certain kinds of risks than those who don't have toxoplasmosis, but it's not yet clear how this happens.

Related: Why do cats hate car rides?

Toxoplasma gondii can live in most mammals, but its life cycle traditionally involves living first inside a mouse or rat. That's likely because cats prey on rodents, giving the parasite a way to reach the cat gut — the only known place where the parasite can reproduce, as cat guts are rich in linoleic acid, an ingredient necessary for Toxoplasma gondii sex, a 2019 study posted on the preprint database bioRxiv found. 

To aid this transition from vermin to feline host, Toxoplasma gondii has a pretty disturbing technique: brain manipulation. The parasite alters the behavior of rodents, making them less afraid of taking risks. It is also known to make mice attracted to the scent of cat poop. In other words, the parasite does something to the brain of mice and rats to make them more likely to dart out in front of a cat to then be caught, killed and eaten. Humans are not immune to Toxoplasma gondii — in fact, at least a third of the world's population is thought to have toxoplasmosis, the infection this parasite causes. Some humans get infected when they clean out their pet cat's litter box, but many of us simply eat undercooked meats or unwashed vegetables. So, what does this mean for the one in three of us who end up playing host to the parasite? 

"When you first get infected, you might have mild flu-like symptoms but most of us don't even realize. If you're a pregnant women then it's more concerning because it can harm the child, but largely, infected people show almost no health issues or noticeable symptoms," said Markus Fitza, a professor of strategy and entrepreneurship at the Frankfurt School of Finance and Management in Germany, whose research has focused on how the parasite can affect decisions made in the business world. 

But that's not where the story ends. "The fundamentals of the human brain are fairly similar to that of a mouse in the grand scheme of things," he told Live Science.

In short, just like an infected mouse is more adventurous, an infected human is also more prone to take risks — sometimes with pretty devastating consequences. At least two studies — one analyzing 370 people in Turkey and another looking at nearly 600 people in the Czech Republic — have shown that people who test positive for Toxoplasma gondii antibodies are more likely to have a car crash. There isn’t a lot of evidence to explain why and how latent infections of toxoplasmosis might affect people’s personalities, such as making them less afraid of risk. The researchers behind the car crash studies, however, wrote that the parasite leaves behind life-long cysts in the brain, which is thought to increase the production of dopamine (a chemical messenger in the brain that is known to affect people's risk and reward calculations), and that may have a role to play.   

Related: Why do our brains have folds?

Toxoplasmosis is also linked to rage problems. People with the psychiatric disorder known as Intermittent Explosive Disorder, or IED, were twice as likely to have a toxoplasmosis diagnosis than healthy individuals with no psychiatric diagnosis, Live Science previously reported.

Interestingly though, a decreased fear of peril may also have its advantages. Fitza's own work has shown that entrepreneurs are more likely to be infected than the general population and that entrepreneurs with the parasite tend to earn, on average, $6,000 more per year than those without it. In one study, he and colleagues tested nearly 1,500 biology and business studies students at a major U.S. university. The results showed that business majors were 1.4 times more likely to test positive for the parasite than biology majors, and within business majors, those specializing in entrepreneurship were 1.7 times more likely to test positive over students in less risky business studies subspecialties. 

Fitza also tested 197 professionals attending entrepreneurship workshops and events. He found that 124  of them had been infected by the parasite. Of those 124 professionals, 17 had started their own business compared with just four out of the 73 non-infected people who attended the same events. While his sample size was small, the findings have been backed up by subsequent, larger studies. The working theory is that Toxoplasma gondii  is manipulating people's brains into making them less afraid of quitting their jobs and going it alone to start up their own company. "We can't say for sure this is what's happening," said Fitza. "But this is the argument we're making based on our studies."

However, scientists have yet to pin down a direct way that Toxoplasma gondii might control human minds, Live Science previously reported. In rodents, it's possible that the parasite secretes molecules that somehow rewire the brain; others think it may be due to brain cysts interfering with dopamine production; and another idea is that Toxoplasma gondii triggers inflammation in rodent brains, which may, in turn, change brain behavior and function, a 2019 study in the journal mBio found. 

That said, humans with toxoplasmosis aren't mindless zombies doing the parasite's bidding. When in humans, there is no benefit to the parasite in making human behavior more risky; any effects are just a hangover from it manipulating the mouse brain, which is advantageous to the parasite. But given that the parasite might lead to some behavioral changes in humans, be mindful of that if you have cats and you're driving your car to a potential business opportunity. 

Originally published on Live Science.

When scientists recently X-rayed a fish's head, they found a gruesome stowaway: A "vampire" crustacean had devoured, then replaced, its host's tongue.

The buglike isopod, also called a tongue biter or tongue-eating louse, keeps sucking its blood meals from a fish's tongue until the entire structure withers away. Then the true horror begins, as the parasite assumes the organ's place in the still-living fish's mouth.

Biologist Kory Evans, an assistant professor in the Department of BioSciences at Rice University in Houston, Texas, discovered the tongue biter while digitizing X-rays of fish skeletons. He shared images of the surprising and horrifying find on Twitter on Aug. 10: "Mondays aren't usually this eventful," Evans joked in the tweet.

Related: What the heck?! Images of evolution's extreme oddities 

There are about 380 species of tongue-eating isopods, and most target a specific fish species as their host, according to the Two Oceans Aquarium in Cape Town, South Africa. This type of isopod enters a fish's body through the gills, latches onto the tongue and begins to feed, releasing an anti-coagulant to keep the blood flowing. The parasite grips the base of the tongue tightly with its seven pairs of legs, reducing the blood supply so that the organ eventually atrophies and drops off, according to the Australian Museum. 

From that point on, the isopod's body serves as a functional tongue for the fish, while the tongue biter continues feeding on the fish's mucus, according to Rice University's Coral Reefs Blog. This partnership between a fish and its living tongue can continue for years; in many cases, fish have been known to outlive their tongue-replacing parasites, Stefanie Kaiser, a postdoctoral fellow at the National Institute of Water and Atmospheric Research in Wellington, New Zealand, told the American Association for the Advancement of Science.

Evans encountered the fish and its macabre "living tongue" as part of a scanning initiative for a family of coral reef fishes called wrasses, he told Live Science. The project's goal is to generate a 3D X-ray database of skeletal morphology for this fish group, making it available to researchers around the world, Evans said. He often shares examples of the scans on Twitter, under the hashtag #backdatwrasseup.

That morning, "I was doing something called digitizing," he explained. "I compare skull shapes of all these different fish to each other, that requires placing landmarks — digital markers — on different parts of the body." In one particular wrasse, a herring cale (Odax cyanomelas) from New Zealand, Evans noticed something odd in the mouth cavity. 

"It looked like it had some kind of insect in its mouth," Evans said. "Then I thought, wait a minute; this fish is an herbivore, it eats seaweed. So I pulled up the original scan, and lo and behold, it was a tongue-eating louse."

Even when wrasses haven't been parasitized by these tongue-biting horrors, they are still extremely weird, Evans told Live Science.

"They have a second set of jaws in their throat, like in the movie 'Alien,'" he said. "Wrasses can swallow a snail, and then they can actually generate enough force with the second set of jaws to crush the shell up in their throat."

Some wrasses called parrot fish have copper-reinforced beaks that are tough enough to bite through coral. And the slingjaw wrasse (Epibulus insidiator) can launch its jaws forward up to 65% the length of its head, to snap up evasive prey. 

"It's like if you saw a Cheeto on the other side of your kitchen, and you just throw your jaws at it while standing in place," Evans said.

Originally published on Live Science.

When it comes to dating in the abyssal depths of the ocean, appearance doesn't matter much. That's fortunate for anglerfish, which resemble nightmarish fanged potatoes with a little reading lamp on top. And those are just the females.

If you've never seen a male anglerfish before, you're not missing much. Measuring just a few centimeters long on average, male anglers are a mere fraction of their partners' size, and contribute a fraction of the work to their relationships. For many anglerfish species, the male's sole responsibility is to permanently latch onto an obliging mate, fuse his circulatory system with hers, then slowly allow his eyes, fins and most of his internal organs to degenerate until he becomes what biologist Stephen Jay Gould called "a penis with a heart." The male gets constant nourishment; the female gets sperm on demand. The anglerfish circle of life spins on.

It's beautiful, we know. But this unique mating ritual — which biologists call "sexual parasitism" — has long stumped researchers. How could the female angler's immune system even allow such a permanent, parasitic union to occur? Humans have a hard-enough time accepting organ transplants that don't precisely match their own tissues, so how does a female anglerfish's body accept a male's (or, in some cases, up to eight simultaneous males) so willingly? A genetic study published July 30 in the journal Science finally offers an answer: Anglerfish mating is only possible because the fish have somehow evolved away some of their most crucial immune defenses.

"For humans, the combined loss of important immune facilities observed in anglerfishes would result in fatal immunodeficiency," study co-author Thomas Boehm, director at the Max Planck Institute of Immunobiology and Epigenetics in Germany, said in a statement. "We assume that as yet unknown evolutionary forces first drive changes in the immune system, which are then exploited for the evolution of sexual parasitism."

Related: Photos: The world's freakiest-looking fish

In the new study, Boehm and his colleagues analyzed the genomes of 10 different species of anglerfish, including species that fuse permanently during reproduction and species that fuse only temporarily. In both groups, the team found a clear absence of genes crucial to the fish's antibody response — that is, how effectively the fish's immune system is able to find and identify foreign invaders.

For anglerfish that fuse permanently during mating, even more immunological hardware was missing. In addition to lacking even more genes related to antibodies, the perma-fusers also lacked genes responsible for encoding killer T cells, which normally attack infected cells or foreign tissues, the researchers said. Overall, it seemed that evolution had totally deleted the adaptive immune system — the part of the immune response that identifies and attacks specific foreign invaders — from these sexually parasitic fishes.

Strangely, anglerfish seem to have had no problem adapting to the deep sea — an ecosystem with no shortage of parasitic microbes — despite their missing immune machinery. It's likely, the researchers wrote in the study, that anglerfish compensate for their lack of adaptive immunity with a beefed-up innate immune system. In other words, they must have some pre-existing, nonspecific defenses that protect them from a wide variety of pathogens without interrupting their invasive mating process.

It's still unclear what those inborn defenses might be — but, whatever they are, they only make anglerfish an even more unique outlier among the world's vertebrates. It may be hard to believe, but it looks like anglerfish are even weirder than we thought.

Originally published on Live Science.

Male cicadas infected by a particularly gruesome parasitic fungus become zombies with an undercover mission: They broadcast a female's sexy come-hither message to other male cicadas, luring their unsuspecting victims to join the zombie cicada horde.

Researchers recently discovered this unusual twist to the cicada's already horrific zombification story. As the parasitic fungus called Massospora eats away at a cicada's abdomen, replacing it with a mass of yellow spores, the fungus also compels males to flick their wings in movements that are typically performed by females to attract mates.

Healthy males that hurry over for female company, then try to mate with the infected male, which passes along the Massospora infection. This and other new discoveries are helping scientists to piece together how Massospora turns cicadas into mind-controlled zombies, according to a new study published online June 18 in the journal PLOS Pathogens. 

Related: Mind control: See photos of zombie ants

This zombie-host relationship can be challenging to observe. Though the fungus can affect cicadas that emerge annually, many of its cicada hosts are in the Magicicada genus, also known as periodical cicadas. These black-bodied and red-eyed cicadas spend 13 to 17 years (depending on the species) underground as immature nymphs. Luckily for the scientists who study periodical cicadas, local populations known as broods that follow this cycle emerge during different years in different locations.

"It would be very difficult to maintain a research program and train scientists if new samples only arrived every 13 to 17 years," said lead study author Brian Lovett, a researcher with the Division of Plant and Soil Sciences at West Virginia University (WVU).

"Road trips to collect from and observe broods are very common among cicada researchers," Lovett told Live Science in an email. "Aside from 'following the brood,' 'sharing the brood' [providing colleagues with access to collected specimens] is also standard practice." 

Once the cicadas emerge and molt their exoskeletons, they enjoy just a few weeks of life on the surface as adults, mating and laying eggs before dying.

However, for cicadas infected by Massospora, life takes an ugly turn. About a week after being infected, fungal spores devour the cicada's abdomen and its body disintegrates — but the insect doesn't die. Rather, it continues to fly around and disperse the zombifying spores far and wide in a process known as active host transmission (AHT), in which a parasite manipulates its living host. 

As Lovett and his colleagues reported, one form of that manipulation compels infected males to imitate female behaviors, moving their wings to lure and infect even more cicadas.

"To our knowledge, this is the only example of AHT in which the pathogen behaves at least in part as a sexually transmitted disease," as transmission sometimes happens when males attempt to copulate with other males, the researchers wrote in the study. 

At least some of the chemical cues responsible for the cicadas' unnatural behavior are psychoactive; one of these is psilocybin, which is also found in hallucinogenic mushrooms, Live Science reported in 2019. But though scientists have identified some of the chemicals in Massospora fungus, the spores' mechanisms for controlling its cicada host have yet to be explained, according to the study.

"These discoveries are not only super cool but also have a lot of potential in helping us understand insects better, and perhaps learn better ways to control pest species using fungi that manipulate host behaviors," study co-author Angie Macias, a WVU doctoral candidate, said in a statement.

"It is almost certain that there are undiscovered Massospora species, never mind the other AHT (active host transmission) fungi, and each of these will have developed its own intimate connection with its host's biology," Macias said.

Originally published on Live Science.

That tickle in your throat?  It could be allergies, irritation or even COVID-19. 

But here's one explanation that may not be on your radar: a worm wriggling in your tonsils. 

At least, that was the cause of one woman's sore throat in Japan, according to a new report of the case.

The woman likely contracted the parasitic worm after eating sashimi, or raw rish, according the report, published July 8 in The American Journal of Tropical Medicine and Hygiene.

The 25-year-old woman went to the hospital after experiencing pain and irritation in her throat for five days. Her symptoms began after she consumed "assorted sashimi," the report said. Doctor's soon identified the culitrp: a 1.5-inch (38 millimeter) black worm in her tonsil.

Further tests revealed that the woman had been infected with Pseudoterranova azarasi, a parasitic roundworm, that typically infects marine mammals such as walruses and seals, Newsweek reported. However, humans can contract the worm through consumption of raw fish or squid, Newsweek reported. When Pseudoterranova is seen, it is usually found in the stomach, and infections in the throat are rare, the report said.

Pseudoterranova belongs to the same family as a more common parasitic roundworm called Anisakis simplex, which also causes stomach infections.

Doctors were able to remove the worm with tweezers, and the woman's symptoms improved rapidly, the report said.

Originally published on Live Science. 

Ancient Cambrian fossils have preserved the oldest known example of parasites in action.

More than 500 million years ago in what is now southern China, tubelike parasites clung to the shells of tiny sea creatures called brachiopods and slurped up their hosts' meals.

Brachiopods are sessile suspension feeders, which means they live fixed in place and capture drifting food particles that are suspended in water. The alignment of the tube-shaped creatures in the newly described fossils suggests that the parasites positioned themselves to intercept food as it flowed toward their host, scientists reported in a new study.

Related: The 10 most diabolical and disgusting parasites

Parasites come in a range of fascinating shapes and sizes. There are near-microscopic dots of parasitic fungus that dine on millipede genitals; parasitic plants that feast on fungus; mind-controlling parasitic protozoans that make rats brazenly approach their predators; and even a parasitic crustacean that devours a fish host's tongue and then replaces the organ with its own body.

Examples of parasitism in the fossil record are also diverse, "from fleas on mammals to mites on insects, and even potentially single-celled parasites on Tyrannosaurus rex," said study co-author Timothy Topper, a research fellow at Northwest University in Xi'an, China and at the Swedish Museum of Natural History in Stockholm.

It can be hard to tell from individual fossils how parasites affected their hosts. But in the newly described fossils, "we have hundreds of specimens of brachiopods — with and without tubes —that have allowed us to statistically demonstrate, for the first time in a Cambrian fossil example, that a host (brachiopod) is negatively impacted by a parasite (encrusting tubeworms)," Topper told Live Science in an email. 

During the Cambrian period, about 512 million years ago, dense colonies of ocean-dwelling Neobolus wulongqingensis brachiopods clustered at a site now known as the Wulongqing Formation in Yunnan, China. These brachiopods measured on average 0.09 inches (2.4 millimeters) wide and 0.08 inches (1.9 mm) long and were abundant there, with approximately 60,000 individuals covering about 11 square feet (1 square meter), the study authors reported.

Researchers looked at 429 of these brachiopod fossil specimens; of those, 205 were infected by parasites, which were probably soft-bodied, wormlike, filter-feeding animals that lived inside the mineralized tubes. Some shells had only three or four parasites, but others hosted seven or more, according to the study.

After the scientists examined and compared the brachiopods, they found that parasite-encrusted specimens were notably smaller than their parasite-free neighbors. The researchers also discovered that the parasites' tubes were positioned so that the worms' heads would have poked out over the curved edge of the host's shell and into the stream of nutrient-bearing water that fed the brachiopods. 

This hinted that the worms were kleptoparasites — food-stealers — and suggested that when they infested brachiopods that were still growing, the worms stole so much food that they stunted their hosts' growth, the scientists reported.

Tube-dwelling, suspension-feeding marine worms known as serpulids are known to parasitize modern brachiopods and bivalves, sometimes infesting them heavily, Topper told Live Science. "But how exactly they impact their host, in terms of growth or biomass, is unclear," he added.

Could the ancient parasites have provided any benefit to their hosts in exchange for stealing their food? It's possible that the worms' mineralized tubes may have given the brachiopods some protection against predators, but more analysis would be required to say for sure, lead study author Zhifei Zhang, a professor in the Department of Geology at Northwest University in China, told Live Science in an email.

"Demonstrating that parasitism existed in the earliest animal communities, is really just the first step in understanding their impact upon the history of life," Topper said. "I think we've only barely begun to scratch the surface of understanding the early evolution of parasitism."

The findings were published online today (June 2) in the journal Nature Communications.

• In images: A filter-feeding Cambrian creature
• Photos: 'Naked' ancient worm hunted with spiny arms
• Photos: A Cambrian larva with a 'daggerlike' tail

Originally published on Live Science.

Researchers have discovered a parasitic fungus that sucks nutrients out of the reproductive organs of millipedes. They named it after Twitter.

Meet Troglomyces twitteri. This near-microscopic parasite looks like a larva and is about 100 micrometers long — comparable to the average diameter of a human hair. Each spore spends its entire lifecycle hanging around the genitals of a single male or female millipede. However you may feel about Twitter, the researchers who discovered the unfortunately-placed parasite weren't trying to throw shade at the social media site when naming this newfound fungus; rather, they were paying homage to how the parasite was discovered.

According to study co-author Ana Sofia Reboleira, an entomologist at the Natural History Museum of Denmark at the University of Copenhagen, the parasite first came to her attention when she saw a colleague share a photo of a North American millipede on Twitter. Two strange, white dots flecked the millipede's exoskeleton; Reboleira instantly pegged them as parasites.

Related: 6 times parasites grossed us out in 2019

After examining several American millipede specimens in the museum's collection, Reboleira and her colleagues found more examples of the novel fungus, which nobody had ever noticed or described before.

"Until then, these fungi had never been found on American millipedes," Reboleira said in a statement. "As far as we know, this is the first time that a new species has been discovered on Twitter."

T. twitteri belongs to the insect-loving fungal order Laboulbeniales, and is one of about 30 species in the order that exclusively attack millipedes. With its head buried beneath its host's exoskeleton and its bum poking into the air, T. twitteri parasites feast on nutrients from one end, while the other prepares spores to infect their next victim. Millipede mating (an intimate affair that can resemble human mating, only with a lot more legs) provides the parasites with a perfect opportunity to spread their spores, likely explaining why the study authors so often detected them near the hosts' reproductive parts, the team wrote.

While millipede-infecting Laboulbeniales were never seen in North America until now, they have been spotted widely around the world, including in Europe, Asia, Africa, the Middle East, Australia and New Zealand. Many of these species were only discovered in the last six years, leading Reboleira to suspect that there are many, many more of the creepy crawlies out there waiting to be discovered. It'll take a lot of retweets to find them.

The study was published May 14 in the journal MycoKeys.

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• Images: Human Parasites Under the Microscope
• The 10 most diabolical and disgusting parasites

Originally published on Live Science.

Toxoplasma gondii, a "mind-controlling" parasite that causes the disease toxoplasmosis, has been found in public lands in Oahu, Hawaii for the first time, researchers have discovered. 

Though this parasite was previously found in people and in wildlife on the Hawaiian islands, it was unknown in Oahu's parks. And it hitchhiked there in free-ranging cats, which are a non-native species and are known hosts of the parasite. Thanks, cats.

Though, to be fair, cats aren't really to blame; people are the ones who first brought cats to the island and then allowed them to roam free. Felines that were abandoned then bred in the wild and formed feral colonies. These cat communities now threaten to expose local wildlife to a harmful and potentially deadly parasite, scientists wrote in a new study.

Related: 7 strange facts about the 'mind-control' parasite Toxoplasma gondii

Toxoplasma gondii is transmitted from cats to other animals — including humans — when cats expel the parasite in feces, in a capsulelike eggs, or oocysts. Once T. gondii oocysts enter a new host they transform to an actively multiplying form called tachyzoites, which can replicate so quickly that they overwhelm the host's immune system and lead to serious health problems.

One of the ways that Toxoplasma gondii affects mice and rats is by tweaking their brain chemistry to change their behavior. Rodents typically avoid cats, but under T. gondii's "mind control" they seek out felines. And that's exactly what T. gondii wants, because the infected rats need to be ingested by cats in order for T. gondii to complete its life cycle. 

And cats' impact on native wildlife doesn't stop with mind-controlling parasites; they are also highly efficient and deadly predators. Cats kill an estimated 2.4 billion birds per year in the U.S. alone, according to the Hawaii Invasive Species Council (HISC). They have contributed to the extinction of 33 island species and are recognized as the principal threat to 8% of all critically endangered reptiles, birds and mammals worldwide, according to the HISC.

Researchers recently looked for feral cat colonies and signs of Toxoplasma gondii at 32 locations on Oahu's parks and public lands inhabited by native bird species. They identified 25 cat colonies near places where native birds were plentiful. The exact number of cats in each colony was uncertain, but the scientists spotted roughly 23 cats on average at every location. Humans were feeding cats at most of these colonies, evidence suggested.

The scientists also gathered 56 fecal samples from four of the cat colonies. Three out of four of those colonies had cats shedding T. gondii, with about 10% of the samples testing positive for T. gondii. 

"The high percentage of T. gondii-positive feces samples suggests that Oahu's cats are contributing large quantities of this infectious parasite to parks and neighborhoods across the island," study co-author Grant Sizemore, the director of Invasive Species Programs at American Bird Conservancy, said in a statement. 

"What's particularly worrying is that these hardy oocysts move through the environment with the potential to infect any warm-blooded species in terrestrial, freshwater or marine ecosystems," he said.

As the team collected feces at only four locations, it's likely that T. gondii is even more widespread on Oahu — "and possibly other islands" — and poses an even greater threat to vulnerable native wildlife, the study authors reported.

"Our results should be considered an absolute minimum, and the occurrence of T. gondii in Oahu's environment is almost certainly higher," they wrote.

The findings were published online April 9 in the journal Conservation Science and Practice.

Editor's note: This article was updated on April 16 to clarify that while T. gondii had previously been found in humans and wildlife in Hawaii, this new evidence is the first to identify the parasite on public lands, and to link that presence to domestic cats.

• In photos: The peskiest alien mammals
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• In photos: Bizarre parasites from the past

Originally published on Live Science.

A newfound species of parasitic worm wiggles its way into the brains of baby lizards long before the reptiles hatch. 

How do the nematodes break into developing lizard brains? They sneak in through the lizard mothers' ovaries, a surprising new study finds.

Parasitic nematodes that prey on mammals can sometimes jump from mother to offspring through the placenta in utero or through breast milk after birth, the study authors noted in an article-in-press to be published in the May 2020 issue of the journal The American Naturalist. But until now, no one thought that reptiles could pass down their parasites from mother to offspring; evidence suggested that, because they lay eggs, animals like lizards are less vulnerable to certain routes of parasitic transmission. 

But much to scientists' surprise, the discovery of worms in lizard embryos suggests that reptilian eggs aren't as impenetrable as once thought.

Related: 8 awful parasite infections that will make your skin crawl

"I was shocked when I saw something moving in the embryo's brain, despite having dissected many lizard eggs before," lead author Nathalie Feiner, an evolutionary biologist at Lund University in Sweden, said in a statement. While studying common wall lizards (Podarcis muralis) across Europe, Feiner and her colleagues routinely dissect and examine developing lizard embryos and find most to be worm-free. However, one population of common wall lizards in the Pyrenees mountain range turned out to be riddled with nematodes.

Wondering where the worms came from, the researchers examined the lizard mothers and found nematodes wriggling in the animals' ovaries. Typically, nematodes invade the intestines of common wall lizards, but the authors hypothesized that this newfound species adapted to thrive in the reproductive system of females. The worms in the ovary infiltrate the embryos of the the developing lizards and enter their brains before a hard egg shell forms around the animal. 

The authors allowed several infected lizard embryos to develop to maturity, noting that "infected lizard embryos develop normally and hatch with nematodes residing in their braincase." The animals appear healthy when first hatched, parasites aside, but the researchers did not monitor the lizards further to see how their health and behavior might be affected as they mature, the authors added. 

"It would be exciting to know if this vertical transmission [between mother and embryo] is unique to the nematodes we found in the common wall lizards or if this occurs in other species, as well," Feiner said. "It would also be interesting to find out if the lizard’s behavior is affected by having worms in their brains."

• The 10 most diabolical and disgusting parasites 
• Ick! 5 alien parasites and their real-world counterparts 
• 7 strange facts about the 'mind-control' parasite Toxoplasma gondii 

Originally published on Live Science. 

When the parasitic blob known as Henneguya salminicola sinks its spores into the flesh of a tasty fish, it does not hold its breath. That's because H. salminicola is the only known animal on Earth that does not breathe.

If you spent your entire life infecting the dense muscle tissues of fish and underwater worms, like H. salminicola does, you probably wouldn't have much opportunity to turn oxygen into energy, either. However, all other multicellular animals on Earth whose DNA scientists have had a chance to sequence have some respiratory genes. According to a new study published today (Feb. 24) in the journal Proceedings of the National Academy of Sciences, H. salminicola's genome does not. 

A microscopic and genomic analysis of the creature revealed that, unlike all other known animals, H. salminicola has no mitochondrial genome — the small but crucial portion of DNA stored in an animal's mitochondria that includes genes responsible for respiration.

Related: These bizarre sea monsters once ruled the ocean

While that absence is a biological first, it's weirdly in character for the quirky parasite. Like many parasites from the myxozoa class — a group of simple, microscopic swimmers distantly related to jellyfish — H. salminicola may have once looked a lot more like its jelly ancestors but has gradually evolved to have just about none of its multicellular traits. 

"They have lost their tissue, their nerve cells, their muscles, everything," study co-author Dorothée Huchon, an evolutionary biologist at Tel Aviv University in Israel, told Live Science. "And now we find they have lost their ability to breathe." 

That genetic downsizing likely poses an advantage for parasites like H. salminicola, which thrive by reproducing as quickly and as often as possible, Huchon said. Myxozoans have some of the smallest genomes in the animal kingdom, making them highly effective. While H. salminicola is relatively benign, other parasites in the family have infected and wiped out entire fishery stocks, Huchon said, making them a threat to both fish and commercial fishers.

When seen popping out of the flesh of a fish in white, oozing bubbles, H. salminicola looks like a series of unicellular blobs. (Fish infected with H. salminicola are said to have "tapioca disease.") Only the parasite's spores show any complexity. When seen under a microscope, these spores look like bluish sperm cells with two tails and a pair of oval, alien-like eyes. 

Those "eyes" are actually stinging cells, Huchon said, which contain no venom but help the parasite latch onto a host when needed. These stinging cells are some of the only features that H. salminicola has not ditched on its journey of evolutionary downsizing.

"Animals are always thought to be multicellular organisms with lots of genes that evolve to be more and more complex," Huchon said. "Here, we see an organism that goes completely the opposite way. They have evolved to be almost unicellular."

So, how does H. salminicola acquire energy if it does not breathe? The researchers aren't totally sure. According to Huchon, other similar parasites have proteins that can import ATP (basically, molecular energy) directly from their infected hosts. H. salminicola could be doing something similar, but further study of the oddball organism's genome — what's left of it, anyway — is required to find out.

• The 10 strangest animal discoveries of 2019
• Ick! 5 Alien parasites and their real-word counterparts 
• The 10 most diabolical and disgusting parasites

Originally published on Live Science.

The award-winning movie "Parasite" recently won audiences' hearts around the world. While that interaction was benign (for most), encounters with real-world parasites are linked to heart disease, and some can seriously disrupt normal cardiac function.

Parasitic infections in humans can lead to myocarditis, a disease that causes heart tissue inflammation. Parasites can also cause pericarditis, an inflammation of the membrane around the heart; and cardiomyopathy, a disorder that impedes pumping and can lead to heart failure, researchers reported in a study published in the journal Clinical Microbiology Reviews.

For Valentine's Day, here are a few of the parasites that can impact heart health. 

You're welcome.

Related: The 10 most diabolical and disgusting parasites

Toxoplasma gondii

A microscopic organism called Toxoplasma gondii is responsible for the disease known as toxoplasmosis. It can be transmitted to humans through contact with cats, and may affect up to 2 billion people worldwide (though most develop no symptoms, according to the Centers for Disease Control and Prevention, or CDC). 

T. gondii can persist in heart muscle, where it forms tissue cysts that can remain through the host's lifetime, and heart disease may be linked with chronic infection of T. gondii, researchers reported in the Journal of Clinical Medicine Research.

Entamoeba histolytica

This parasite is the primary cause for amoebiasis, or amoebic dysentery, a colon infection marked by abdominal pain and diarrhea, according to the CDC. But in rare cases this parasitic infection can lead to a serious heart complication known as amebic pericarditis, in which it causes abscesses in the pericardium — the saclike membrane surrounding the heart, scientists wrote in the Journal of Clinical Medicine Research. 

People with pericarditis often experience sharp, stabbing chest pain caused by the irritated pericardium walls rubbing against each other, the Mayo Clinic says.

Trichinella spiralis

Trichinella spiralis is a parasitic roundworm that targets carnivorous and omnivorous mammals around the world. It infects people who eat the undercooked meat of infected animals, entering the human hosts as larvae-filled cysts and causing the disease trichinosis, according to the CDC.

After a host swallows the cysts, stomach acid dissolves the sac and releases the larvae into the body; eventually they circulate into the blood and burrow into muscles and brain tissue. Severe complications from the parasite can include heart tissue inflammation and life-threatening arrhythmia, or irregular heartbeat, researchers reported in the journal StatPearls. 

Echinococcus granulosus

Tapeworms in the Echinococcus genus can infect people when their eggs are ingested after contact with feces from a dog or other canids, scientists reported in the journal Clinical Microbiology Reviews (CMR). The eggs hatch and the six-hooked embryos cross the intestinal wall and travel to organs to form cysts, the CDC says. 

Cardiac cysts are rare, but can lead to irregular heartbeat; accumulation of fluid in the sac surrounding the heart; fainting due to high blood pressure; heart attacks and even sudden cardiac arrest, according to the CMR study. 

Trypanosoma cruzi

Trypanosomiasis, or Chagas disease, is caused by the parasite Trypanosoma cruzi, and is transmitted to people through bites from insect vectors, according to the CDC.

About 30% to 40% of people infected by T. cruzi develop heart complications associated with chronic Chagas disease, such as heart rhythm abnormalities, a dilated heart that doesn’t pump blood effectively, and congestive heart failure, the Mayo Clinic says.

In many cases, symptoms can appear 10 to 30 years after the victim was first infected, researchers wrote in the journal Clinical Microbiology Reviews.

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Originally published on Live Science.