The risk of malaria influenced where prehistoric people lived in sub-Saharan Africa, a new study suggests.

The research is the first to link early human habitation with the deadly disease and contrasts with early assumptions that prehistoric people migrated to different regions mainly for agricultural reasons.

In the study, researchers analyzed existing models of climate and environmental data that indicate where malaria was likely prevalent, and compared it with maps of early human settlements. They found that prehistoric humans seem to have avoided regions where malaria was endemic long before the introduction of farming in sub-Saharan Africa between about 3000 and 1000 B.C.

"For a long time, it was thought that infectious diseases only really became a problem with the advent of farming, and this was particularly true of malaria," study co-author Eleanor Scerri, an archaeological scientist at the Max Panck Institute of Geoanthropology in Germany, told Live Science in an email.

But the study by Scerri and her colleagues, published April 22 in the journal Science Advances, suggests that humans have avoided settling in areas with a high risk of malaria for more than 70,000 years.

"Our work shows that we can no longer ignore diseases in the deep human past," she said. "They don't just have a small effect, they have — in the case of malaria, at least — transformative impacts that have helped to shape who humans are today."

Malaria risks

The study authors used data from earlier studies to reconstruct the climate of sub-Saharan Africa over the past 74,000 years in intervals of between 1,000 and 2,000 years.

Then, they calculated a "malaria stability index" for each area at every step, based on modern epidemiological data and the likelihood that an area contained habitats for the Anopheles genus of mosquito. The bites of female Anopheles mosquitoes transmit the parasite Plasmodium falciparum to humans, which causes malaria.

By comparing this index to maps of early human settlements, the authors showed that prehistoric hunter-gatherers in sub-Saharan Africa had actively avoided high-risk malaria hotspots. The researchers said that this behavior, in turn, helped determine human population structures by at least 13,000 years ago — several thousand years before the introduction of farming.

"The key message from our paper is that malaria was already a bit of a problem before agriculture," study co-author Andrea Manica, an evolutionary ecologist at the University of Cambridge, told Live Science. But "it likely became even worse after people became sedentary and settled at high density as a consequence of food production."

The study suggests that Central West Africa was hardest hit, he added, and the region remains a malaria hotspot today.

"Archaeology in Central West Africa is limited, but a number of findings agree with a view that populations in this area were highly fragmented," Manica said.

Malaria hotspots

The study is the first to suggest that the locations of prehistoric human settlements were influenced by the risk of disease, rather than just changes in the climate — although both rainier and warmer weather would have encouraged populations of disease-carrying Anopheles mosquitoes.

"The role of disease in the deep human past, particularly in the earliest, African phases of our species' prehistory has not been well investigated because we lack ancient DNA from those time periods," Scerri said.

But the new study showed how the lack of evidence could be overcome. "We have developed a pipeline that is capable of exploring a number of vector-borne diseases," Scerri said. "It's an exciting breakthrough and we hope it will open up a new field of inquiry."

"We have shown that it is possible to track a disease back in time and assess its potential impact on past inhabitation," Manica added. "The next phase is to start exploring other diseases besides Plasmodium falciparum to see their role."

Simon Underdown, a biological anthropologist at Oxford Brookes University in the U.K., who was not involved in the new study, said he agreed with the study's conclusions.

"Disease has always been with us, and it actually shaped what humans could do, where humans could move," he told Live Science.

See how much you know about early humans with our human evolution quiz!

Update, Oct. 21, 2025 at 1:17 pm ET: Live Science has learned that Iceland is no longer mosquito-free. Three mosquitoes — two females and one male — were found in the garden of a private residence between Oct. 16 and Oct. 18 in the municipality of Kjósarhreppur (also known as Kjós), according to the Iceland Monitor. In a Facebook post in the group Skordýr á Íslandi ("Insects in Iceland"), the man who found them, Björn Hjaltason, said "I could tell right away that this was something I had never seen before."

Matthías Alfreðsson, an entomologist at the Icelandic Institute of Natural History, confirmed that the mosquitoes belong to the species Culiseta annulata, the Iceland Monitor reported.

"The last fortress has fallen," Hjaltason wrote in the Facebook post, although it still remains to be seen if the mosquitoes will survive Iceland's winter.

The original article, posted Sept. 1, is below.

Mosquitoes bite people in almost every country across the globe. But are there any countries that don't have this blood-sucking pest?

The answer is "yes," there is one country without mosquitoes: Iceland. While its neighbors — including Norway, Scotland and Greenland — are home to multiple mosquito species, Iceland remains mosquito-free. (Of note, Antarctica is also mosquito-free, but the southern continent is not a country.)

So how is it possible for Iceland to have no mosquitoes?

Scientists have several theories. One idea is that mosquitoes simply haven't made it to Iceland yet. The island nation is separated from its neighbors by hundreds of miles of ocean, creating a natural barrier that makes it difficult for mosquitoes to arrive by flight.

Yet mosquitoes do get transported aboard planes. Gísli Már Gíslason, a professor emeritus of limnology (the study of lakes and fresh water) at the University of Iceland, confirmed this after capturing a mosquito on a flight from Greenland to Iceland. Furthermore, mosquitoes can survive for hours on aircraft landing gear, even in freezing temperatures, he said in an interview with Reykavík Grapevine, an English-language publication in Iceland, in 2017.

So if mosquitoes have arrived, why haven't they established populations?

Gíslason explained that a lack of suitable breeding habitats is unlikely. Iceland has plenty of ponds and marshes near its airports — ideal places for mosquitoes to lay eggs. Instead, the most probable explanation is Iceland's harsh climate.

A mosquito's life cycle consists of four stages: egg, larva, pupa (like a caterpillar chrysalis) and adult. Adult mosquitoes lay their eggs in water. These eggs hatch into larvae, which develop in pupae. An adult mosquito then emerges from the pupa.

Robert Jones, an insect biologist and assistant professor at the London School of Hygiene & Tropical Medicine, told Live Science that mosquito larvae require unfrozen liquid water to develop. In extremely cold regions like the Canadian Arctic, some mosquito species survive by entering dormancy in the egg stage, where they can endure months of frozen water.

"In warmer areas, such as parts of Central Europe, mosquitoes may survive the winter as eggs or larvae in relatively sheltered bodies of water that do not freeze, or as adults hidden in burrows and other protected sites," he said.

Iceland's climate falls in between: Long winters and frequent freeze-thaw cycles in autumn and spring cause water bodies to freeze, melt and refreeze repeatedly. "These cycles disrupt development and kill mosquito eggs and larvae before they can emerge as adults, making it much harder for populations to establish," Jones said.

Although Iceland's geothermal pools remain unfrozen in winter, their temperatures may be too warm for larvae of any mosquito species adapted to high latitudes. "In addition, the chemical composition of geothermal waters is unlikely to be suitable for mosquito development," he said.

However, with climate change, Iceland's mosquito-free status might not last forever. Jones noted that warmer springs and autumns could create longer periods of unfrozen standing water, allowing mosquitoes to establish permanent populations.

Immo Hansen, a professor of biology at New Mexico State University, agrees. "We're currently seeing tropical mosquitoes expanding their range north in the United States," he told Live Science, largely because that region's winters are warming.

If mosquitoes do eventually spread to Iceland, it wouldn't be the first time a mosquito-free zone disappeared. Hawaii, the most isolated archipelago in the world, was mosquito-free until 1826, when European and American ships inadvertently introduced them. Thanks to Hawaii's favorable climate, mosquitoes thrived and spread rapidly across the islands. Since then, climate change has pushed mosquitoes into Hawaii's higher-elevation forests that were once too cool for them to survive.

Despite the potential for mosquitoes to arrive in Iceland, the risk of disease-carrying species — like those in the Aedes genus, which are known to transmit diseases such as dengue and chikungunya — establishing there remains low because these insects need tropical and subtropical climates to survive, Jones said. While Southern Europe faces increased risks of such outbreaks due to climate change and modern transport, "modeling studies suggest that Northern Europe will remain largely unsuitable for dengue transmission even by 2080," he said.

Are we running out of time to stop climate change? Nearly a year has passed since the Intergovernmental Panel on Climate Change (IPCC) warned that limiting global warming to the 1.5-degree Celsius (2.6 degrees Fahrenheit) mark by the end of the century — a goal set to stave off the worst impacts of climate change — "would require rapid, far-reaching and unprecedented changes in all aspects of society." 

Some politicians and writers have thrown their hands up in the air and argued that it's too late, and that human civilization is simply not up to the task. Others, meanwhile, took the report as a call to arms, reframing one of its points as a political organizing message: We have only 12 years to stop climate change, and the clock is ticking. (A year later, we're down to 11.)

But the full picture is both more and less dire than a slogan can capture. We can't stop climate change — because it's already here, and it's already too late to reverse many of its catastrophic effects. What's true is that things are on track to get much worse over the course of this century, and that if we're going to stop those things from happening, society is going to have to start hitting some important deadlines fast. There's a big one coming 12 years after the IPCC report. Blowing through it won't immediately plunge society into a "Mad Max"-style dystopia, as some have suggested — perhaps tongue in cheek — but it will make sure everything keeps getting steadily worse, and it will make turning things around down the road that much harder.

Related: The Reality of Climate Change: 10 Myths Busted

Some scientists are nervous that overemphasizing the 2030 deadline might mislead the public about the nuances of climate change. But others pointed out to Live Science that activists have a task that's different from that of researchers — one that requires straightforward goals and clear, simple ideas.

The IPCC report, which the U.N. climate science body released Oct. 8, 2018, revealed that the best path to limiting warming to an increase of 1.5 C by 2100 involves cutting net human carbon dioxide (CO2) emissions 45% by 2030 (12 years after the report was published) and then cutting emissions further to net zero by 2050. It was far from the first dire warning that the agency had issued. But this one seemed to take root in the public discourse around climate change, possibly because of how news stories summarized the report. An Oct. 8, 2018, headline in The Guardian read, "We have 12 years to limit climate change catastrophe, warns UN." Vox headlined its article "Report: we have just 12 years to limit devastating global warming." Smithsonian.com wrote, "The World Was Just Issued 12-Year Ultimatum On Climate Change."

In an interview with writer Ta-Nehisi Coates three months later, on Jan. 21, Rep. Alexandria Ocasio-Cortez, D.-N.Y., spelled out how the report's conclusions had entered the zeitgeist:

"Millennials and Gen Z and all these folks that come after us are looking up, and we're like, 'The world is going to end in 12 years if we don't address climate change, and your biggest issue is how are we gonna pay for it?'"

Here's the thing: Scientists never said the world was going to end in 12 years if we don't stop climate change. Even researchers known for ringing the alarm bells on climate change are far more likely to speak in terms of decimal places and nonlinear effects than to talk about the end of civilization as we know. 

Prominent activists rarely bring up doomsday, either. Messages from the Global Climate Strike organizers and the U.S.-based Sunrise Movement focus on long-term climate shifts, not an impending, sudden disaster. Still, the 12-year deadline looms large in the culture.

"It has achieved an absoluteness in its role in societal dialogue that's not in line with scientific fact," said Katharine Mach, a climate scientist at the University of Miami and one of several lead authors of the IPCC report.

"The world will not end if we pass 1.5 degrees Celsius of warming above preindustrial levels," Mach said. 

Related: 8 Ways Global Warming Is Already Changing the World

And failing to hit a 45% reduction target won't lead to 1.5 C of warming by 2030, as Lini Wollenberg, a University of Vermont climate researcher and leader of the CGIAR Research Program on Climate Change, Agriculture and Food Security, told Live Science. It does, however, increase the chances of hitting 1.5 degrees C by 2100 and experiencing many more climate catastrophes on our way through the 21st century, Wollenberg said.

The issue is that any program set up to mitigate warming will have two basic components: short-term cuts to emissions and longer-term efforts to pull carbon out of the atmosphere. (This doesn't necessarily mean giant, futuristic CO2-sucking machines, but may mean things like growing forests.)

"Some people — I'm hazarding industry and those focused on maintaining a growth-focused economy — would argue that we don't want to sacrifice things in the short term, and that society will figure out the technology to deal with it later," Wollenberg said.

But every year of delay on cutting greenhouse gas emissions means that carbon-capture efforts down the road will have to be even more fantastical and dramatic (including heavy reliance on carbon-capture technologies that may never work). And each year in which we do nothing, the world will cross more climate tipping points that will be difficult to undo, Wollenberg said.

The year 2030 has been bouncing around climate-policy documents for a while, Wollenberg said. (It also turned up in the Paris Agreement, for example, as did the goal of net zero by 2050.) Researchers saw that target as part of a reasonable time frame for drawing down emissions without it resulting in unbearable economic costs or having humanity rely too heavily on future carbon-capture efforts, she said.

"It could have been 2020, 2012 or 2016," Wollenberg said, adding that 2030 "used to seem a lot further away."

The 1.5 C target was picked for similar reasons — an effort to balance what's possible against what's necessary. But, similar to the 12-year time frame, 1.5 degrees is a target set by scientists, not an immutable scientific fact.

"We know that the risks go up [as temperature rises]. We're already experiencing widespread impacts of the changing climate," Mach said, pointing to the ongoing consequences of 2019's 1 C (1.8 F) of warming above preindustrial levels. "It will be greater at 1.5 degrees of warming, and may go up from there in some very substantial ways … with severe, irreversible impacts."

Holding warming to 1.5 degrees won't reverse climate change. In fact, the catastrophic impacts in that idealized scenario will be much worse than they are now.

Colin Carlson, an ecologist at Georgetown University who studies how climate change influences infectious diseases, said that one problem with imagining that we have 12 years until a huge disaster hits is that such thinking obscures the ongoing horrors of climate change in 2019.

"Climate change has already killed hundreds or thousands — or more — of people," Carlson said, "through malaria, through dengue, through a hundred other avenues that we're only now starting to be able to quantify."

Mosquito-borne diseases flourish in a warming world, his research has shown. And the world has already warmed enough that many people have gotten sick and died from those diseases — people who otherwise would have been spared.

Related: 5 Deadly Diseases Emerging from Global Warming

"So this is not as simple as 'Can we stop this coming?' It's already here," he said.

Similarly, Wollenberg’s work has shown that severe climate impacts are devastating food production worldwide in 2019. Vast regions of North and South America, Asia and Africa are becoming too hot for growing grains. The soil in low-lying, coastal regions of Bangladesh and China is getting saltier as rising seas contaminate groundwater, threatening rice production. (A few places are becoming more hospitable to certain crops. A warming Vermont, for example, is growing more hospitable to peaches, even as a shortened ski season threatens its economy.) The overall impact is to drive up food prices and create global unrest. Long term, these trends will make it impossible for some countries to produce enough food to feed their populations, she said.

To manage all that complexity, researchers tend to break down responses into two broad categories: mitigation and adaptation. Mitigation is, in short, the work of preventing climate change from worsening. Reducing emissions and growing forests fall into this category. 

Adaptation is learning to deal with the warming that's already here and the additional warming that's coming: building sea walls and flood-abating salt marshes around coastal cities; studying changes in precipitation so farmers know when to plant their crops; and engineering crops to better withstand harsh environments.

But ultimately, all the researchers Live Science contacted said these problems become less catastrophic with less warming. Holding the world to a 1.5-C warming increase by the end of the century creates much more manageable short- and long-term problems than holding it to 2 C of warming, which is much less harmful to Earth than 3 C, which is much more survivable than 4 C, which is still less catastrophic than 6 C … and so on. None of those possible futures necessarily leads to a charred, lifeless global desert in our lifetimes. But each increase is almost unimaginably more dire for life on this planet than the one preceding it.

"It's always worth it to prevent more warming," Mach said.

With regard to the spread of mosquito-borne diseases, Carlson said, "We can stop it. Mitigating climate change is truly the silver bullet. Sometimes it is as simple as, 'If we stop climate change, we can stop a lot of the bad health impacts that are coming.'" (Though the devil is in the details, he added. The level of disease reduction will depend on how fast the carbon-mitigation project moves, and its effects won't be felt immediately or equally everywhere.)

The science points relentlessly to one reality: The best way to deal with climate change is to start cutting emissions now. It's easier to stop warming by keeping CO2 in the ground now than it is to pull carbon out of the air later. And mitigation makes adaptation much more effective. 

Bringing up the 12-year time frame, then, is a way of drilling down on the first step the world has to take to move down the most effective mitigation path still available — even if it doesn't capture the full scope of the issue.

So, is it irresponsible for public figures to employ the 12-years rhetoric?

"I think the role of public figures is to set visions and create the urgency that we need," Wollenberg replied. "The scientific community is sometimes uncomfortable with that, but if you started talking to the general public about, 'Well, you could trade off your long-term emissions and delay the decline by 5%, or we could do a 4% reduction every year, but that would contrast with a 7% reduction where we could wait until 2035,' it would not be an effective message."

“I would blame the public figures who aren't taking steps more than I would blame the people who are trying to promote a vision," she said.

We're at a point in time when people are feeling the effects of climate change on their lives, said Jewel Tomasula, a doctoral student ecologist at Georgetown University, who studies the health of salt marshes in New Jersey. As Live Science has previously reported, the world in 2019 is hotter, monster storms are more frequent, diseases are on the move, and fires and floods are happening more often. Talking about 2030, Tomasula said, is about creating a window for activism to take effect — a decade of meaningful global movement on the problem.

"Science is great for understanding the problem," she said. "Climate change is a physical problem, and we can work on it with our data and really understand it. But that's not what's really going to fix it. … The way that problems like this have been addressed in the past is by having that political will and mobilization."

The notion of a 12-year deadline can be misleading and obscures some of the hedging and nuance scientists like to emphasize. But it also seems to offer climate mobilizers a focal point for their efforts, and people really are getting out into the streets.

• 6 Unexpected Effects of Climate Change
• Images of Melt: Earth's Vanishing Ice
• 5 Ways Climate Change Will Affect Your Health

Originally published on Live Science.

DEET works because mosquitoes can taste your body with their legs, and it makes them think your skin tastes super gross, according to a new study.

The chemical has long been known to be the most effective mosquito repellent available, but researchers weren't sure why or how it worked. The new study, available online in advance of publication May 6 in the journal Cell Current Biology, showed that DEET doesn't taste especially gross to mosquitoes' mouths. Rather, they really don't like the way it feels to the tongue-like cells on their feet.

"We were confident then that DEET was doing something interesting and fairly unique on the surface of the skin," lead study author Emily Dennis, a neurogeneticist at Princeton University, said in a statement. (Dennis was a graduate student at Rockefeller University when she did the DEET research.)

That's because, while DEET tastes bitter to mosquitoes that drink it, it doesn't taste any more bitter than other bitter chemicals. And Dennis had previously worked on a team that showed that DEET doesn't keep mosquitoes from landing on people. Only once the mosquitoes land, the researchers showed, does the effect of the repellent kick in and drive the mosquitoes away. [Googly Eyes: Photos of Striking Wasp Faces]

This new work had six stages:

First, the researchers offered mosquitoes one of three foods: sugar water, sugar water mixed with DEET or sugar water mixed with another bitter chemical. The insects preferred the plain sugar water to either chemical mixture, but didn't distinguish between DEET and the bitter substance.

Second, they slathered the skin of their arms in the bitter chemical at very high concentrations. The mosquitoes, they found, were still happy to land on the skin, puncture through it, and drink the clean blood beneath.

Third, they offered the mosquitoes a serving of warm blood protected by a skin-like membrane. When the DEET or other bitter substances were mixed into that blood, they found, the mosquitoes didn't drink it.

Fourth, they tested those compounds on the surface of the membrane with clean blood beneath. Bitters on the membrane weren't effective at stopping the insects from drinking. But with a layer of DEET on the membrane, the mosquitoes still landed on it but immediately took off.

Fifth, they offered the mosquitoes blood beneath a patch of DEET-coated skin that was too small for them to simultaneously drink from and touch with their legs. The mosquitoes still drank, suggesting that they weren't just reacting to the way DEET felt to their mouthparts.

Sixth, and finally, they used a special glue to partially block the taste buds on the mosquitoes' legs. The insects still drank blood beneath DEET-coated skin, albeit less often, suggesting that the legs in particular were experiencing the repelling sensation when DEET worked.

So when you're outside, coated in DEET, know this: You still smell good enough to mosquitoes. They still want to drink your warm blood. But your skin tastes super gross to their legs.

• Gallery: Out-of-This-World Images of Insects
• Goliath Birdeater: Images of a Colossal Spider
• The Cutest Bugs in The World

Originally published on Live Science.

This story was updated Sept. 29 at 12:25 p.m. EDT.

A person in Florida has caught a locally transmitted case of dengue fever, news sources reported Wednesday. The case is the first in which a person caught dengue from a mosquito bite within Miami-Dade County in 2016.

The person diagnosed with the viral infection has received treatment and is expected to fully recover, CBS Miami reported. The case is also Florida's second local dengue case of 2016, according to CBS Miami. In 2015, the state reported one locally transmitted case of dengue, and in 2014 it had six known locally acquiered cases of the disease, according to the Florida Department of Health. 

Dengue (pronounced den' gee) is a disease caused by four closely related viruses: DENV 1, DENV 2, DENV 3 and DENV 4, according to the Centers for Disease Control and Prevention (CDC). It's spread when infected mosquitoes — usually the species Aedes aegypti, but sometimes the species A. albopictus — bite humans. [7 Devastating Infectious Diseases]

The virus cannot be spread directly from person to person; it must be carried by a mosquito, according to the CDC.

There are an estimated 100 million cases of dengue worldwide yearly, according to the CDC. Symptoms of the infection include high fever, severe headache, severe pain behind the eyes, joint pain, muscle and bone pain, and rash, the CDC said. Symptoms usually begin within 14 days after a person is bitten, and can last up to one week, CBS Miami reported.

There isn't a specific treatment for dengue, but people with the disease can take pain relievers, such as Tylenol, that contain acetaminophen; drink plenty of fluids; and consult with a physician, according to the CDC. If the person develops severe symptoms, such as vomiting or severe abdominal pain, he or she might have dengue hemorrhagic fever, a potentially fatal disease that can be treated if caught early, according to the CDC.

Officials in Miami-Dade County are working to reduce mosquito populations, and "aggressive mosquito control is being conducted in this county already to address Zika," said Mara Gambineri, the communications director at the Florida Department of Health. In general, to prevent the dengue virus from spreading, people can get rid of standing water where mosquitoes breed, and use window screens and air conditioners to stop the insects from getting inside, according to the CDC. (Mosquitos prefer humidity, and air conditioners make the air inside drier.)

People can also wear long-sleeved shirts, pants and insect repellant to avoid mosquito bites, according to the CDC.

Florida isn't the only state to experience dengue. Hawaii had dengue outbreaks in 2001, 2011 and 2015, and Brownsville, Texas, had an outbreak in 2005. An outbreak in Key West, Florida, stretched from 2009 to 2011, Jonathan Day, a professor of medical entomology at the University of Florida, told Live Science in 2015.

However, there are no animals other than mosquitoes in the United States that can carry dengue, and so effective mosquito control can play a big part in getting rid of the disease, once the human outbreak ends, Day said.

Editor's Note: This story was updated to include more information from the Florida Department of Health.

Original article on Live Science.

Health officials in Florida are investigating a case of Zika that may have been acquired locally rather than in another country. But if the virus is spreading in Florida, how did it get there?

For someone to acquire Zika in Florida, a person infected with Zika would have to spread the virus to a mosquito, which then would spread it to another human.

For example, a new chain of "locally acquired" cases of Zika could happen if a Florida resident were to travel to a country where Zika is spreading, become infected with the virus and then return to Florida, where they would be bitten by a mosquito while the Zika virus was in their blood. This would make that mosquito capable of transmitting Zika to another person in Florida.

If the Zika virus has indeed found its way into the local mosquito population in Florida, it wouldn't be a surprise, experts say. The type of mosquitoes that carry Zika, called Aedes mosquitoes, are known to live in Florida.

"It was only a matter of time before the right mosquito found the right person," said Dr. Amesh Adalja, an infectious-disease specialist and a senior associate at the University of Pittsburgh Medical Center's Center for Health Security. Two other types of mosquito-borne viruses — chikungunya and dengue — have already spread from other countries to the United States in the same way, Adalja said. [Zika Virus News: Complete Coverage of the 2016 Outbreak]

When a local mosquito initially bites a person infected with the Zika virus, it takes 10 to 15 days before the mosquito is able to transmit the virus to another person, Laura Harrington, a professor and chair of the Department of Entomology at Cornell University, told Live Science in an interview in February. That's because it takes time for the virus to make its way to the mosquito's salivary glands, where it can be transmitted to another person.

But once the virus reaches the salivary glands, the mosquito can transmit the virus for the rest of its life, Harrington said. (The mosquitoes that can carry Zika usually live about 15 days.)

Officials in Florida have not released much information about the new case. A statement from the Florida Department of Health issued yesterday (July 19) said that officials are investigating "a possible nontravel-related case of Zika virus in Miami-Dade county."

To determine whether the new Zika case was acquired locally, officials will likely first check the patient's travel history, to see if he or she has been to an area where Zika is spreading, Adalja said. Officials will also ask whether the patient has had sexual contact with anyone who traveled to an area where Zika is spreading, because the virus can be transmitted sexually.

And because a person in Utah may have caught the virus after caring for someone with Zika, officials will likely also check whether the Florida Zika patient had cared for someone with Zika.

But if none of these things happened, "it leaves you with the possibility that this was acquired locally," Adalja said. Officials would then likely check local mosquitoes to see if they are carrying the virus, he said.

Even if it turns out that Zika was acquired from a mosquito in Florida, health officials have said they do not expect widespread transmission of the virus in the United States. That's because, unlike in many countries where the virus has been spreading, the American lifestyle tends to limit exposure to the mosquitoes — people spend more time indoors here than people do in the South and Central American countries where the virus is currently spreading.

People in the U.S. also usually have screens on their windows and use air conditioning, all of which prevent exposure to mosquitoes, Adalja said. And standing water, where mosquitoes breed, tends to be less of a problem in the United States than it is in some other countries, he said.

The main way to prevent the spread of Zika by mosquitoes is to control the mosquito population, Adalja said. That usually involves spraying insecticide to kill mosquitoes and cleaning up areas where mosquito populations breed.

Officials could also release genetically modified mosquitoes that are not capable of producing offspring, Adalja said. This strategy has been used in other countries to prevent the spread of mosquito-borne diseases but hasn't been tried in the United States, in part because of the anti-GMO movement in this country, Adalja said.

In a recent study, Adalja and his colleagues surveyed people living in Key West, Florida, about their attitudes toward genetically modified mosquitoes, and found that most people opposed releasing these mosquitoes. But that study was conducted before the rise of Zika, and people's attitudes may have changed since then, Adalja said. The virus has been linked to severe neurological problems in babies born to women who are infected during pregnancy.

The large number of Zika cases occurring worldwide "will hopefully change opinions there," Adalja said.

Original article on Live Science.

Many people in the U.S. are not aware of key facts about the Zika virus, according to the results of a new poll.

Researchers found that, for example, in households that included a woman who was either pregnant or considering getting pregnant in the next year, 1 in 4 people were not aware of the link between the Zika virus during pregnancy and microcephaly, a birth defect that causes an abnormally small brain and head.

"We have a key window before the mosquito season gears up in communities within the United States mainland to correct misperceptions about Zika virus so that pregnant women and their partners may take appropriate measures to protect their families," Gillian SteelFisher, director of the poll and a health policy research scientist at the Harvard T.H. Chan School of Public Health, said in a statement. [Zika Virus News: Complete Coverage Of The Outbreak]

The researchers recently polled 1,275 people in the U.S., including 105 people who live in households with a woman who is pregnant or considering getting pregnant in the next 12 months.

They found that, among the people who live in such households, 1 in 5 incorrectly believed that there is a vaccine against the Zika virus infection.

Moreover, 4 in 10 did not know that the virus can be sexually transmitted, the researchers found. In addition, a quarter said they thought that people infected with Zika are "very likely" to show symptoms of an infection. (In reality, only about 1 in 5 people infected with the virus show any symptoms of the infection, according to the Centers for Disease Control and Prevention.)

These results suggest that this key group of people — those who are pregnant, trying to get pregnant, or close to someone who is pregnant or trying — does not have accurate information about the Zika virus, the researchers said.

The findings also suggest that researchers or doctors need to get this information to women and their partners, SteelFisher said.

In their study, the researchers also found that the public, and not just people in households with pregnant women, also have certain misperceptions about the virus. [The 9 Deadliest Viruses on Earth]

For example, 4 in 10 people believe that, if a woman who is not pregnant becomes infected with the virus, it is likely to harm her potential future pregnancies. However, according to data provided by the CDC, "the Zika virus infection in a woman who is not pregnant would not pose a risk for birth defects in future pregnancies after the virus has cleared from her blood."

The CDC currently recommends that women who do become infected with Zika wait eight weeks from the time their symptoms started before trying to become pregnant. 

Though the vast majority of people know that the Zika virus is transmitted by mosquitoes, many of them have misperceptions about other facts related to its transmission. For example, 4 in 10 people are unaware that the virus can be transmitted sexually. And about a third mistakenly believe that the virus is transmitted through coughing and sneezing, the researchers found.

Such misperceptions could either prevent people from taking precautions they need to take, or they could lead them to take precautions that are inappropriate or unnecessary, SteelFisher said.

Follow Agata Blaszczak-Boxe on Twitter. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

The first vaccine trials against the Zika virus will likely start this fall, federal health officials announced today (March 10).

President Barack Obama has asked Congress to approve $1.8 billion in federal spending to battle Zika virus, but so far, Republicans in Congress have put up a fight, insisting that health officials should use federal money left over from the Ebola crisis, according to USA Today. Officials from the Centers for Disease Control and Prevention (CDC) said in a news briefing today that it will be difficult for vaccine trials to move forward to subsequent stages unless Congress grants the funds needed to fight the disease.

And health officials say using the money earmarked to fight Ebola isn't the answer. "The idea that we should rob Peter to pay Paul and hope that Congress replaces money that's essential to keep America safe is frankly, I think, too dangerous to do," Dr. Tom Frieden, director of the CDC, told reporters, according to The Hill. [Zika Virus News: Complete Coverage of the 2016 Outbreak]

The mosquito-borne virus has sickened thousands of people in South and Central America. Only about 1 in 5 people infected with the virus show symptoms, such as fever, rash and muscle pain, but the disease is thought to be far more dangerous for pregnant women. Mounting evidence suggests that if a pregnant woman is infected with Zika, her fetus may be at increased risk of developing microcephaly and other developmental disorders.

Caring for one child affected by the Zika virus in utero could cost about $10 million over a lifetime, Frieden said.

Scientists are hard at work on a vaccine, but it could take years before a successful Zika vaccine clears Food and Drug Administration (FDA) regulations, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told reporters.

"We believe we can get a vaccine," Fauci said, adding that he felt "cautiously optimistic" because scientists have produced vaccines against other flaviviruses, a group that includes Zika, yellow fever, dengue and West Nile.

So far, Phase 1 clinical trials are slated to start by the end of summer or early fall of this year, he said. Phase 1 trials are small, and are held to evaluate whether a treatment is safe, what dosages are best and what side effects participants report.

If the vaccines given in the Phase 1 trial pass muster and can induce an immune response against the virus, then scientists can proceed to Phase 2 by early 2017, Fauci said. But unless Congress approves the funds, health officials may not have enough money to put together a Phase 2 trial right away, and the entire process may take longer to complete, he said.

Furthermore, private pharmaceutical companies may be hesitant to partner with the government if funding isn't certain, Fauci said. This hasn't happened yet, but it has happened to other drug and vaccine development programs in the past, he added. [10 Deadly Diseases That Hopped Across Species]

Puerto Ricans fight Zika

Meanwhile, the CDC is working on other ways to prevent Zika infections in places like Puerto Rico, where the virus is becoming established. The U.S. territory is approaching its rainy season, a time when mosquitoes thrive. Health experts expect that thousands of pregnant women in Puerto Rico will become infected with the virus this year, Friedman said.

The CDC is running several pilot programs that will determine the feasibility of installing window screens on local dwellings. However, many houses have open eaves, and so installing screens on windows would have little or no impact, Friedman said.

Workers are also spraying insecticides to try to diminish mosquito populations, federal officials said.

The United States is also researching the best ways to prevent Zika infections, and health officials plan to gather at the CDC-hosted Zika Action Plan Summit on April 1 to address the upcoming mosquito season, which typically begins in June or July in the United States, Frieden said.

Follow Laura Geggel on Twitter @LauraGeggel. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

Some pregnant women with Zika virus tend not to fare well, and neither do their fetuses, a new study finds.

Zika is a mosquito-borne virus that can also be transmitted through unprotected sexual intercourse. Because of concerns that the disease may increase the risk of microcephaly (small brain size) and other developmental disorders in the fetuses of pregnant women infected with the virus, scientists decided to monitor the pregnancies of both healthy and infected women.   

The researchers studied 88 pregnant women in Rio de Janeiro from September 2015 through February 2016, according to the study, published Friday (March 4) in the The New England Journal of Medicine. Of these women, 72 tested positive for Zika virus in their blood, urine, or both. [Zika Virus News: Complete Coverage of the 2016 Outbreak]

Among the Zika-positive pregnant women, the most common symptoms were rash, joint pain, red eye and headache, the researchers found. The doctors also performed a fetal ultrasound on 42 of the women with Zika and on all of the women without Zika. Among the Zika-positive group, 12 of them (29 percent) had fetuses with abnormalities, compared to none of the 16 Zika-negative women.

Among the 12 fetuses with abnormalities, two of them died — one at 36 weeks and the other at 38 weeks. Five of the fetuses were smaller than normal (and some had microcephaly), seven had central nervous system lesions, and seven had an abnormal amount of amniotic fluid or cerebral or umbilical artery flow, the researchers said. One fetus had additional problems, including microcephaly and other brain development challenges, growth restriction and a potential clubfoot, they added.

To date, eight of the 42 women who participated in the ultrasound have given birth, and the ultrasonographic findings have been confirmed, the researchers said.

"Despite mild clinical symptoms, Zika virus infection during pregnancy appears to be associated with grave outcomes, including fetal death, placental insufficiency, fetal growth restriction and central nervous system injury," the scientists said in the study.

The findings are "quite disturbing," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told reporters today (March 10) in a news briefing. 

Given that fetal abnormalities were found in 29 percent of the Zika-positive women,  it's possible there may be "many more [abnormalities] that you don't realize until after the birth of the baby," Fauci said. 

Moreover, the study shows that the fetuses had developmental problems even when their mothers caught the disease late in their pregnancies. 

"In all three trimesters of pregnancy, there were definite fetal effects," Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, told reporters in today's briefing. "What we're saying basically is that the more we learn about Zika in pregnancy, the more concerned we are."

Follow Laura Geggel on Twitter @LauraGeggel. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

The rapid spread of a disease called Zika virus urgently requires attention, two leading researchers say.

Zika virus is the most recent in a list of viruses that were formerly confined to remote niches of the world but are now expanding their reach into the Northern Hemisphere.

Much about these viruses is still poorly understood, wrote Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases (NIAID), and Dr. David Morens, senior scientific advisor for the NIAID, in an article published in the New England Journal of Medicine on Thursday (Jan. 14).

Zika virus is carried by mosquitos and causes generally mild symptoms like fever and rashes. However, it has recently been linked to an alarming rise in newborns with microcephaly — a condition causing reduced brain development and abnormally small heads — in Brazil. Ten times as many cases were reported there in 2015 than in previous years, according to the Centers for Disease Control and Prevention (CDC).

In their new article, Fauci and Morens evaluated the extent of the threat posed by this fast-spreading virus.

Health officials have been aware of Zika virus for 60 years, but it is only within the past year that data gathered from infected populations hinted at the more severe consequence of infection, the researchers said. [Tiny & Nasty: Images of Things That Make Us Sick]

In French Polynesia, an epidemic of diverse neurologic conditions happened concurrently with Zika virus outbreaks, suggesting an association between the two. And some public health officials have attributed the recent and alarming spike in infants with microcephaly in Brazil to Zika infections contracted by women while they were pregnant.

However, Fauci and Morens warn, it's too soon to conclude that Zika virus is definitely responsible for these conditions. Commercial tests for Zika are yet to be developed, and it is possible that a closely related disease, like dengue virus, actually caused some suspected Zika infections, the researchers said.

"Intensive investigative research" is required to look at the possible link between the virus and the birth defects, Fauci and Morens said. But even if no link is discovered, researchers must learn more about Zika, they said.

Expanding north

On Dec. 31, the CDC reported the first locally acquired Zika virus case in Puerto Rico, farther north in the Americas than ever seen before. And on Monday (Jan. 11), a traveler who had recently returned to the United States from Latin America was diagnosed with Zika in Houston, according to the Texas' Harris County Public Health and Environmental Services (HCPHES).

Harris County officials stated that the infected person had symptoms "that are often associated with the Zika virus, which include fever, rash and joint pain."

This case isn't a cause for alarm — Zika can't spread directly between people, and as of Jan. 14 there have been no reports of anyone acquiring the illness while in the United States, according to the CDC.

However, one species of the mosquito group known to carry Zika, the Aedes genus, is common across North America. This bug, called the Asian tiger mosquito, carries viruses related to Zika, such as chikungunya and dengue, and is especially common in U.S. states that border the Gulf of Mexico, as shown by a species distribution map created by the CDC.

As yet, there is no vaccine against Zika and no cure for the infection. But Fauci and Morens wrote that they are skeptical about the benefit of pursuing a vaccine to halt Zika's spread, suggesting that vaccines are an inefficient solution to epidemics that appear seemingly out of nowhere. Vaccinating entire populations could be prohibitively expensive, the authors added.

The more promising course, they wrote, would include implementing public health strategies that respond more quickly to contain infections before they reach epidemic proportions, and developing broad-spectrum antivirals, rather than following the more traditional treatment approach of "one bug, one drug."

A global effort

Perhaps the most unusual thing about Zika is that "it's not so unusual anymore," said Dr. Bruce Hirsch, an infectious disease specialist with Northwell Health in New York, who was not involved in writing the new editorial. "These exotic infections like Zika, dengue, West Nile and chikungunya are becoming very well-known and familiar," he told Live Science.

Hirsch explained that global warming is likely allowing the mosquitos that carry Zika to range farther north. And as human populations grow and live closer to each other, the risk of disease transmission and the possibility of emerging epidemics increases, Hirsch said.

Perhaps the key to beating these viruses lies in better-coordinated global efforts, Hirsch added. If infections in remote locations can reach the United States' doorstep in a matter of months or weeks, then the global health care community must pay closer attention and respond more immediately to health crises as they develop, no matter where in the world they are, he said.

"We need to understand that monitoring the health of people around the planet is a way to keep our local community safe," Hirsch said.

Follow Mindy Weisberger on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Cases of dengue fever are showing up in the Florida Keys, but not in Tucson, Ariz., and exactly why remains a mystery, said researchers, who studied mosquito populations and human behaviors in both areas to shed light on the similarities and differences between them.

The results of their new study have turned up some clues and ruled out others to help explain why Key West had a dengue outbreak, involving 28 cases, between 2009 and 2010, and Tucson did not. The disease is pronounced DENG-gay.

"Key West and Tucson share a lot of risk factors for dengue fever," said study author Kacey Ernst, an assistant professor of epidemiology at the University of Arizona in Tucson.

Despite Tucson's desert climate differing from Key West's wet, tropical conditions, both locations have large populations of the Aedes aegypti strain of mosquito, which can spread the dengue virus to people.

And both cities have a large number of residents who frequently travel to high-risk countries -- Tucson residents may head south to Mexico, and people in Key West may escape to the Caribbean -- where they can become infected while visiting and introduce the virus into their communities once home. [10 Deadly Diseases That Hopped Across Species]

Although the mosquito-borne illness had largely been eradicated in the U.S. since the 1940s thanks to mosquito-control spraying and prevention programs, dengue has recently reappeared with outbreaks in Florida and Texas.

This disease causes an estimated 100 million infections a year worldwide, according to the national Centers for Disease Control and Prevention. When diagnosed and treated, the disease is not usually fatal, but it can be debilitating, with symptoms ranging from high fever and headache to severe bone and joint pain. The bone and joint pain is so severe that the disease has been called "breakbone fever."

The preliminary findings were presented today (Nov. 14) at the American Society of Tropical Medicine and Hygiene's annual meeting in Washington, D.C.

Florida Keys vs. Tucson

To learn more about people's knowledge of dengue fever, and their attitudes and practices toward preventing it, the researchers surveyed 400 households in Key West and 372 in Tucson.

They found that awareness of dengue fever was higher in Key West than in Tucson, and more people in Key West checked daily in and around their homes for standing water, a prime breeding ground for mosquitoes.

Residents in both cities had a similar use of central air-conditioning, a good strategy to avoid getting bitten. And more people in Tucson reported they applied insect repellant and regularly checked their window screens for holes that might let in bugs.

"We heard a lot about the 'Key West' lifestyle playing a possible role in transmission," Ernst said, meaning that these Floridians love to spend time outdoors and keep their windows and doors open for fresh air.

"But we actually found that there were similar behaviors even in Tucson, where it is quite hot during the summer," she said. 

Dengue tips

Because the study found few differences between the two cities in terms of human behavior or socioeconomic conditions, the preliminary results point to differences between their mosquito populations as a more likely explanation for the outbreak in one but not the other, Ernst told LiveScience.

Although the exact factors that influence the spread of the virus are complex, Ernst speculated that Tucson's climate might possibly be too hot, too dry, or have too wide a gap between its daily high and low temperatures to support mosquitoes living long enough to transmit the disease.

Another possibility is that there may be small flare-ups of dengue fever in Tucson that are not being detected, she said.

The findings also showed that a fairly large portion of the populations in both communities were not engaged in prevention and control strategies, but Ernst suggested there are many things people can do to lower their odds of contracting the disease.

They can reduce their contact with mosquitoes by using repellant and removing standing water, as well as ensuring there are barriers between them and the mosquitoes, such as wearing long clothing and having screens on doors and windows, to prevent bites.

And residents can support community programs to clean up neighborhoods of containers and old tires that can collect water and breed mosquitoes. 

Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.

About 46 million years ago, a mosquito sunk its proboscis into some animal, perhaps a bird or a mammal, and filled up on a meal of blood. Then its luck turned for the worse, as it fell into a lake and sunk to the bottom.

Normally this wouldn't be newsworthy, and nobody would likely know or care about a long-dead insect in what is now northwest Montana. But somehow, the mosquito didn't immediately decompose — a fortuitous turn of events for modern-day scientists — and became fossilized over the course of many years, said Dale Greenwalt, a researcher at the National Museum of Natural History in Washington, D.C. Greenwalt discovered the mosquito fossil after it was given to the museum as a gift, and he immediately realized the specimen's rarity.

It is, in fact, the only blood-engorged mosquito fossil found, Greenwalt told LiveScience. The fossil is even stranger because it comes from shale, a type of rock formed from sediments deposited at the bottom of bodies of water, as opposed to amber, the age-old remains of dried tree sap, in which insect remnants are generally better preserved. [See Photos of Ancient Life Trapped in Amber]

"The chances that such an insect would be preserved in shale is almost infinitesimally small," Greenwalt said.

In their study, Greenwalt and his collaborators bombarded the mosquito fossil with molecules of bismuth, a heavy metal, which vaporizes chemicals found in the fossil. These airborne chemicals are then analyzed by a mass spectrometer, a machine that can identify chemicals based on their atomic weights, Greenwalt said. The beauty of this technique, called time-of-flight secondary ion mass spectrometry, is that it doesn't destroy the sample — previously, similar techniques required grinding up portions of fossils, he added. The analysis revealed hidden porphyrins, organic compounds found in hemoglobin, the oxygen-carrying protein in blood, hidden in the fossilized mosquito's abdomen.

The finding may bring to mind the story of "Jurassic Park," a novel and movie in which scientists resurrect dinosaurs from DNA preserved in blood-engorged mosquitoes preserved in amber. Although this finding doesn't really make this fictitious story any more likely, it does show that complex organic molecules besides DNA can be preserved for a long time, Greenwalt said.

The discovery also shows that "blood-filled mosquitoes were already feeding at that time, suggesting that they were around much earlier and could have fed on dinosaurs," said George Poinar, a paleo-entomologist at Oregon State University, who wasn't involved in the research.

Greenwalt said he had no way of knowing exactly how the mosquito was preserved so well. Perhaps the most likely hypothesis is that the insect was trapped in a covering of water-suspended algae, which are capable of coating specimens in a sticky, gluelike material, before sinking to the bottom; this algae process has been shown to fossilize other types of insects, he said.

Researchers don't know what kind of animal the blood came from, since hemoglobin-derived porphyrins amongst different animals appear to be identical, Greenwalt said.

The study is exciting, because it provide more evidence that porphyrins, organic compounds found in "virtually all living organisms from microbes to humans in varying amounts" are "extremely stable" — and are thus a perfect target for studying long-dead plants and animals, said Mary Schweitzer, a researcher at the North Carolina Museum of Natural Sciences, who wasn't involved in the study. 

Email Douglas Main or follow him on Twitter or Google+. Follow us @livescience, Facebook or Google+. Article originally on LiveScience.

Mosquitos, ticks, worms — these all are 'middle men' when it comes to disease spread. They can carry and transmit bacteria, viruses and other pathogens to us that cause dengue fever, Lyme disease and other vector-borne infections. As one approach to help reduce and even eliminate these diseases in people, researchers funded by the National Institutes of Health are studying the basic mechanisms that let the infection-causing organisms flourish inside their hosts.

A "Mind-Blowing" Bacterium

One such bacterium that scientists are interested in is called Wolbachia.

"It's probably the coolest bacterium in the world," says NIH's Irene Eckstrand.    

Wolbachia infects more than a million species, including insects, shrimp, spiders, mite and tiny worms. It lives and reproduces in its host's cells, primarily reproductive ones. The bacterium can manipulate these cells in ways that boost its own survival and reproductive success.

Seth Bordenstein, a Vanderbilt University scientist who studies Wolbachia, says the bacterium alters the reproductive life of its insect and other hosts in four "mind-blowing ways:"

1)    It kills infected males.

2)    It turns genetic males into females by shutting down certain hormones.

3)    It allows infected females to reproduce asexually.

4)    It promotes the survival of embryos from infected females only.

Ecology and Evolution

"Aside from stimulating the imagination, Wolbachia serves as a tool for studying the evolution and ecology of infectious diseases," notes Eckstrand, who co-manages an NIH-National Science Foundation program that's dedicated to this topic.

When Bordenstein, whose research is supported through the program, started studying Wolbachia about a decade ago, scientists thought that the bacterium and ones like it didn't frequently acquire new genetic machinery. The theory was that living inside other cells isolated the bacterial genomes, inhibiting the exchange of genetic elements with other bacteria that enables evolution.

Since that time, the theory — and Wolbachia itself — have evolved. Bordenstein discovered that Wolbachia can move to different cells and to new hosts, some of which are infected with other types of bacteria as well as different Wolbachia strains. This co-infection allows the bacterium to acquire new genetic elements.

Scientists also have learned that Wolbachia harbors a bacteria-infecting virus, called a bacteriophage, that can introduce other genetic elements. Bordenstein found that Wolbachia's interaction with the bacteriophage and its exchange of genetic elements through co-infections creates a cycle of evolution with implications for how diseases spread.

Disease Control

While Wolbachia doesn't directly infect mammals, it is the root cause of several serious mammalian diseases. It infects parasitic worms that, by way of mosquitos, can cause heartworm in our pets. Other types of Wolbachia-infected worms hitch rides to ultimately reach human hosts, where they can trigger severe inflammatory responses that lead to river blindness and elephantiasis. In an ironic twist, researchers are actually using Wolbachia to help fight these infections.

One strategy that Bordenstein is beginning to explore focuses on bacteriophage enzymes that can wipe out Wolbachia. Some organisms, including the parasitic worms, actually need the bacterium to reproduce. By eliminating the Wolbachia infection, the enzymes could render the worms sterile and unable to further spread disease. 

Scientists also are harnessing Wolbachia's wanton ways to control the spread of dengue virus, which is transmitted to humans by mosquitoes. Researchers have discovered that Wolbachia-infected mosquitoes can't replicate the dengue virus. Releasing more Wolbachia into the mosquito population or finding and introducing the Wolbachia genes that interfere with replication are promising new avenues for reducing the spread of dengue. The approach could potentially apply to other vector-borne diseases like sleeping sickness, which is transmitted by the tsetse fly. 

According to Bordenstein, studying Wolbachia has yielded some surprising new insights on microbial evolution that could help us understand, treat and prevent certain infectious diseases. "It's what gets me up every day and keeps me excited about doing this work," he says.

This Inside Life Science article was provided to LiveScience in cooperation with the National Institute of General Medical Sciences, part of the National Institutes of Health.

Learn more:

Bordenstein Lab, Blog and Twitter Pages

Collection of Articles About Wolbachia

Ecology and Evolution of Infectious Diseases Program

NSF Special Report on the Ecology of Infectious Diseases

Also in this series:

The Quake that Brought Back Cholera

Living Laboratories: How Model Organisms Advance Science

Solving the Sleeping Sickness 'Mystery'

Mosquitoes love to feed on mammalian blood, including that of humans. However, in the Galápagos, these troublesome insects have a unique taste for reptilian blood as well and may pose a threat to the giant tortoises, marine iguanas and other wildlife on the island.

The mosquito, Aedes taeniorhynchus, is a black salt-marsh mosquito that is also found on the North and South American coasts. The mainland version of this species feeds on mammals and birds. But after making its way to the Galápagos, the mosquitoes adapted to the island’s isolation and biodiversity and began drinking reptilian blood as well, according to a new study. The Galápagos Islands, where Charles Darwin honed his evolutionary theory, are an increasingly popular tourism destination, and scientists are now worried that A. taeniorhynchus could aid infectious disease transmission on the island.

"This is a big risk when you have so many tourists," said Arnaud Bataille, the study’s lead author and a Ph.D. student in comparative biology at the University of Leeds. "You have a big risk of spreading disease across wildlife."

The study is detailed in the June 1 issue of the journal Proceedings of the National Academy of Sciences.

Scientists previously thought the mosquito was carried to the islands by humans. But after analyzing a special type of DNA, called mitochondrial DNA, scientists traced the mosquitoes' lineage and learned that they split from their mainland kin and arrived on the islands some 200,000 years ago, long before humans discovered the Galápagos around 1535. Bataille said the mosquito appears to be in the process of evolving into a new species, but further taxonomical studies are needed to confirm this idea. A. taeniorhynchus remains the only species of mosquito that live across the entire island.

In the Americas, A. taeniorhynchus, is known to transmit diseases such as heartworm in dogs, and has the potential to transmit West Nile virus, which is lethal in mammals, birds and reptiles. Those groups of animals are the mosquitoes' three feeding sources on the Galápagos. There is no evidence for such diseases on the island and scientists want to keep it that way.

To prevent transmission, scientists recommend fumigating boats along with continued fumigation of airplanes, to kill non-native mosquitoes. Potentially, a disease-carrying foreign mosquito could infect a mammal or bird on the island. A. taeniorhynchus could then transmit the disease from the infected animal to the Galápagos reptiles.

Since these reptiles evolved without contact with humans or modern infectious diseases, scientists say their immune defenses are unlikely to protect them if an infection occurs.

The research was funded by the UK's Darwin Initiative scheme, an AGAPE Marie Curie Training Centre grant and the Natural Environment Research Council.

• Top 10 Mysterious Diseases
• Top 10 Deadliest Animals
• Gallery – Backyard Bugs

As storm clouds begin to lift over the flooded Midwest, experts are predicting an entirely different sort of deluge. Mosquitoes, which can breed out of control in the puddles and pools left behind as flood waters recede, may be poised to add insult to injury.

Midwesterners aren't the only ones ripe for the biting. Mosquitoes are ubiquitous in the United States, living in every state and capable of thriving in all kinds of climates, according to Joseph M. Conlon, technical advisor to the American Mosquito Control Association (AMCA). Wherever there's standing water, there are mosquitoes, he said. And the diseases they carry, such as West Nile Virus, aren't far behind.

But science has some new solutions in the form of improved repellents, genetically modified mosquitoes, and new approaches to vaccine design, as well as some science-based ideas you can put to use at home.

Control just the mosquito

The big strides in mosquito control have largely involved better eradication and population control efforts, aimed to affect only mosquitoes, leaving other animals intact.

One of the most important developments in this effort was bio-rational control materials, said James Stark, executive director of the Metropolitan Mosquito Control District, the public agency charged with keeping Minneapolis and St. Paul relatively mosquito-free. Developed in the 1980s, these "materials" are actually a strain of naturally occurring wetlands bacteria. The District sprays the bacteria onto lakes and other water sources where mosquito larvae hatch and grow. The larvae then eat the bacteria, which kills them by destroying the walls of the insect's stomach. Only mosquitoes and a few related fly species are susceptible. Other animals, including people, can ingest the bacteria without any damage.

The project, one of the largest in the world, according to Conlon, has had a lot of success with this bacteria, particularly when combined with newer computer database systems that allow the agency to easily map and track areas where the bacteria are needed most.

But a new method, or, rather, a new twist on an old method, is on the horizon.

Sterile insect technique, or SIT, involves breeding large numbers of sterile male insects and then releasing them into the wild. Ideally, the huge influx of sterile males out-compete their normal counterparts in the game of love, creating a whole generation of unfertilized eggs and crashing the insect population. SIT wouldn't eradicate all mosquitoes, but it would keep population levels low enough to control the spread of diseases.

It's a trick that has worked before on other insects, said James Becnel, research entomologist and lead scientist with the USDA's Fly and Mosquito Control Unit. Those past experiments used radiation to sterilize, but that can be problematic with mosquitoes, making them less able to compete for mates.

Now, an English company called Oxytec is pushing a new approach to SIT, using genetically altered mosquitoes. "They have a gene that's sensitive to antibiotics," Becnel said. "You can rear them in the lab with a small amount of antibiotics and grow big numbers. Then, when you release them, there's no wild antibiotics, so the genes are turned on and they become sterile."

This technique could be coming to malaria-stricken Malaysia very soon, according to an article in the May 21 issue of the journal Nature.

Viral vision

Other efforts focus on controlling the ability of living mosquitoes to spread disease among humans. The most obvious way to do this, of course, is through the use of vaccines. But, while there is a vaccine for the tropical Yellow Fever virus, there aren't any for the mosquito-spread illnesses most common in the United States.

In fact, in the case of West Nile Virus, there's a vaccine for horses, but not for people.

This is a funding issue, said the AMCA's Conlon. "Production and distribution of human vaccines is an extraordinarily expensive process and the time investment from concept to commercial production can be as much as 10 years," he said. "There aren't enough people getting sick to make it worthwhile to a company to develop a vaccine."

But a new development in vaccine technology could possibly change that. This week, researchers at Stony Brook University in New York announced they'd developed a new method of designing vaccines that could potentially make the process faster and cheaper.

The researchers, including Steffen Mueller, Bruce Futcher and Steven Skiena, found they could genetically alter viruses to make them weaker and reduce their ability to multiply in the body. In trials, mice fought off a weakened version of polio, leaving them with immunity to the "wild" virus. Details are in the June 26 issue of the journal Science.

The researchers said this method could allow scientists to develop new vaccine candidates much faster than currently possible, basically speeding up the turn-around time between deciding to find a vaccine for a certain virus and having a workable candidate in-hand.

And while much of the expense of developing a vaccine lies in extensive clinical trials, a hurdle which probably won't go away, this new method could cut earlier development costs, and potentially make it possible to create vaccines for diseases that currently don't have one, the researchers said.

Better repellents

Another major area of research is better repellents, which could keep mosquitoes away from people more effectively. Becnel's colleague from the USDA, Ulrich Bernier, along with researchers from the University of Florida, recently made some big breakthroughs in this field.

Using 50 years of data on repellent chemicals, the team trained a brain-based computer program to recognize the molecular structures and components common to effective repellents. Then, they set the program to work analyzing some 2,000 chemical compounds, looking for the ones that shared those traits. The result was 23 newly synthesized compounds that have the potential to outperform all repellents currently on the market, according to the May 27 issue of the Proceedings of the National Academy of Sciences.

In fact, while the most common current repellent, DEET, remains effective in a closed environment for about 17 days, one of the new compounds stuck it out for 85.

This type of data-mining research isn't new, but how it's being applied is. "The pharmaceutical people have been using this method for years to design drugs, but it's just now that the mosquito people are getting into it too," Becnel said.

Home invasion

Actually, fending off mosquitoes doesn't require lab access. Conlon said that folks at home can play along. All you need to do is follow what he calls the Three D's.

Drain: Mosquito eggs need water to hatch. But they don't need large amounts of water. Conlon has seen the bugs breed in everything from discarded bottle caps to creases on tarps. If you don't want mosquitoes breeding in your backyard, you need to be fastidious about removing all sources of standing water, no matter how small.

Dress: Conlon said mosquitoes can bite through tight clothes and are attracted to dark colors. The ideal mosquito-resistant outfits are ensembles that are loose-fitting, long-sleeved, and light-colored. "In particular, they have a hard time seeing the color yellow," he said. "Yellow bug lights can be useful because of this. They don't repel mosquitoes, but they don't attract them, either."

Defend: There are only four active ingredients currently approved by the Food and Drug Administration to effectively and safely repel mosquitoes: DEET, picaridin, ir3535, and, for those who prefer a plant-based option, oil of lemon eucalyptus. Conlon said it's important to look for these ingredients because there are many mosquito repellents on the market that simply don't work.

"Popular folk remedies like garlic and Vitamin B-1 have been shown to be useless in double blind studies," he said. Others, such as oil of clove, are known repellents, but only at high concentrations that would burn human skin. "So it works, but not at the low levels used in any product. There, it just smells nice," he said.

Sting, Bite and Destroy

From ants in the kitchen to pigeons on the stoop, pests torment everyone. They sting, bite, destroy things and carry diseases. We've selected some of the peskiest creatures you're liable to come across and offer tips on how you can safely get rid of them. The first step to a pest-free home is removing their life support: water, food, and shelter.

Superbugs

Overuse of antibiotics has developed this relatively new pest, resistant to almost all antibiotics. Bacteria that cause staph infections, heart valve infections, and pneumonia have outwitted antibiotics in a classic example of Darwinian survival: only the strongest survive an onslaught of antibiotics and are able to reproduce. Their offspring, superbugs, are most often found in hospitals, nursing homes, and other settings where people fall sick often. The best defense is surprisingly simple: Wash your hands

Rats

As the largest single group of mammals on Earth, rats damage buildings by making nests out of insulation, chewing electrical wires and causing fires. In the Middle Ages, millions of Europeans died after being bitten by rodent fleas carrying the plague bacterium. Hide your food and trash from rats, as they also transmit typhus, trichinosis, and food poisoning.

Mosquitoes

To nourish their eggs, female mosquitoes feed on animal and human blood, and in turn transmit diseases like malaria, dengue, and West Nile Virus. Two days after a female lays her eggs, they are ready to hatch, but can withstand drying for months. Prevent hatchings by cleaning up pools of standing water. Fish can be introduced to gobble up the insects too.

Pigeons

Pigeons carry diseases that can inflict humans with weak immune systems, but their mess is their worst offense. Droppings deface buildings and can inflict long-term architectural harm. To avoid the foul dirt, don't feed the birds. Pigeon-proof buildings by replacing damaged roof tiles, sealing holes, and installing spikes or wires where they roost.

Rabbits

Rabbits gnaw on lawns, vegetables, herb gardens, and even plastic irrigation lines, and of course they multiply like themselves. They also can spread a serious bacterial illness called tularemia. To protect Australian farms from these invasive species, construction began in 1901 of the Rabbit Proof Fence, the world's longest-and apparently most inefficient- fence. Keeping rabbits out of a fenced backyard involves plugging every tiny hole.

Cockroaches

Cockroaches need just a crack in the wall as thin as a dime to carry germs into your home. Their ability to adapt is key to their 200-million-year history. Yet, they can only survive without water for a week. Make them thirsty by pouring Lysol into toilet bowls and down drains.

Deer

Deer eat their way through gardens and lawns, cause traffic hazards, and carry deer ticks that transmit Lyme disease. To keep them at bay, plant sweet-smelling plants that they dislike, such as lavender, rosemary and sage. In woodsy areas, tuck pant legs inside socks and check pets regularly for ticks.

Ants

Ants create scent trails to communicate with each other and find their way home. When you spot an ant path, start at the food source and wipe away the trail with soapy water and a sponge. Ants also dislike Vaseline, chili powder, cinnamon, and boric acid, which can be used to block a trail entrance. These methods are unsafe, however, if you have small children.

Flies

While adult houseflies help themselves to your food and drink, they defecate on your meal. In order to digest solid foods, they turn it into liquid by regurgitating it. These unsanitary habits transmit diseases. To defend against the, install screens on doors and windows, and cover your picnic basket.

Bedbugs

Checking the sheets late at night is your best chance of catching these critters in the act of hunting down a midnight snack of warm blood. To stop them from crawling up your bed, coat furniture legs with Vaseline or mineral oil; on the floor, place a barrier of chalk or double-sided carpet tape around the bedposts.

The high-pitched whine of a mosquito might drive you nuts, but it's music to the ears of these little pests.

Scientists have long known that male mosquitoes key in on the buzzing of females to help them find a partner. But a new study finds that female mosquitoes, despite their comparatively simple antennae, are among the best listeners in the insect world.

The research also revealed how the mosquito mating commences.

When two mosquitoes approach each other—typically moving along at about 1 mph—each alters the tone of its buzzing, which is created by the wings beating at up to 600 times each second.

If the tones converge, each knows the other is a potential mate. If the tones diverge dramatically, then they learn they're chasing a same-sex relationship that's not apt to produce any little pests.

It is likely, the researchers say, that different mosquito species (there are about 3,000 of them around the world) employ different flight tones in order to recognize viable mates. 

The study, by Gabriella Gibson of the Natural Resources Institute at the University of Greenwich and Ian Russell of the University of Sussex, is detailed in the July 12 issue of the journal Current Biology.

• Why Ants Rule the World
• Backyard Bugs: The Best of Your Images
• Natural Mosquito Repellent Being Developed
• How Flies Walk on Ceilings
• All About Insects

We all know that one person who comes home from the camping trip without a single bug bite. Perhaps they advise their unlucky mates to eat more garlic, or fewer bananas.

But it may be that these folks are born with a scent that keeps mosquitoes and other biting insects away. Recent research has isolated chemicals emitted by "bug-proof" individuals, which appear to counteract the odors that hungry bloodsuckers generally home in on.

The study showed "unequivocally that there are compounds that interfere with the normal attraction that mosquitoes have towards humans," said John Pickett from Rothamsted Research in England.

Pickett told LiveScience in a telephone interview that he and his colleagues are working on a mixture of these compounds that could serve as a natural insect repellent.

Selective Biting

After his own research showed that certain cows gave off odors that protected the entire herd from flies, Pickett had his grad student, James Logan, look for a similar chemical shield in humans.

There are certain mosquitoes, like the one that transmits yellow fever in Africa, for which human blood is the preferred meal, but it is not known exactly how these insects locate their hosts. Carbon dioxide and heat are thought to be attractors, but these emissions are not peculiar to humans.

There must be some human scents that particular insects pick up on. For people who rarely get bitten, the prevailing wisdom had been that they do not emit these chemical flags.

"Usually what you think is that a mosquito flies around and then smells something juicy that it goes after," Pickett said.

But he and Logan have shown that everyone is "juicy" to some extent. It is just that certain individuals exude chemicals that mask the attractive smells or simply repel biting insects.

Mosquito sensing

To isolate these unattractive compounds, the researchers found volunteers who kept yellow fever mosquitoes at bay. The chemical emissions from these bite-resistant people were collected from their hands or from their entire bodies, using a special foil sleeping bag.

To determine which of these chemicals mosquitoes can smell, the scientists attached tiny wires to the antennae of several insects and then exposed them to individual compounds.

"We can put electrodes across the antennae of a live, but immobilized, insect," Pickett said. "We record the potential - which changes when the mosquito senses something."

Once a substance was found to be perceptible, it could be tested for its repellant properties. The mosquitoes were placed into a y-shaped tube and given the choice of moving upwind along either branch. An attractive odor wafted down both branches, but only one branch had the particular scent being tested.

The researchers discovered 11 compounds that the yellow fever mosquitoes consistently avoided.

Product potential

The results have not yet been published, as the research team is still looking at how effective mixtures of the 11 unattractive compounds are at warding off mosquitoes. The goal is to come up with a marketable product.

Pickett said this potential repellent should be effective on all sorts of biting insects - not just yellow fever mosquitoes. They have already tested some of the compounds on the Scottish biting midge and Anopheles gambiae - the mosquito that spreads malaria - and have seen similar results.

Currently, most insect repellents contain DEET, which is a synthetic compound. Although the Environmental Protection Agency has found DEET to be safe if used properly, Pickett thinks that natural chemicals, which some of us emit from our bodies, could make for a better repellent.

There are natural products already available for combating bugs, but they are generally plant extracts, like citronella, which try to cover up our animal smell.

"They are not very effective," Pickett said. "Mosquitoes can often see through these disguises."