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Deadly hemorrhagic fever in Bolivia can spread between people

An image shows microscopic specimens from the arenavirus family. The Chapare virus, like Lassa virus and Machupo virus, is from the arenavirus family.
An image shows microscopic specimens from the arenavirus family. The Chapare virus, like Lassa virus and Machupo virus, is from the arenavirus family.
(Image: © Centers for Disease Control and Prevention)

A deadly animal virus that causes fevers, abdominal pain, vomiting, bleeding gums, skin rash and pain behind the eyes can now spread between people, the Centers for Disease Control and Prevention (CDC) announced Monday (Nov. 16).

Until now, there had been only one confirmed case of Chapare virus, an Ebola-like illness that turned up in the rural Bolivian province of Chapare in 2004 and then disappeared. But in 2019, at least five more people caught the bug, according to research now made public. The virus spread from person to person through bodily fluids in a region near Bolivia's capital city of La Paz, killing three people. There are no active outbreaks of Chapare in 2020, and even in the event of further outbreaks the virus would be unlikely to cause a pandemic, according to virus experts.

There are reasons to be concerned about the news, however. Three of the five confirmed patients from the 2019 outbreak were health care workers, according to a CDC statement; a "young medical resident," an ambulance medic and a gastroenterologist all contracted Chapare after contact with bodily fluids from infected patients. Two of them died.

Hemorrhagic fevers such as Ebola rarely spread as widely as respiratory illnesses like the flu or COVID-19, Colin Carlson, a Georgetown University researcher who studies zoonotic diseases, told Live Science. That's because hemorrhagic fever symptoms typically appear soon after infections (as opposed to the long incubation periods of respiratory illnesses), and direct contact with bodily fluids is generally necessary to catch a hemorrhagic disease. But outbreaks can devastate health care systems, with huge numbers of health care workers becoming sick after treating infected patients.

A new outbreak

The first hint of the 2019 Chapare outbreak was found in a collection of bodily fluids that turned up in a government laboratory in the Bolivian city of Santa Cruz. The doctors who collected the samples believed the patients had contracted dengue, a potentially fatal mosquito-borne illness that can also cause fever and internal bleeding."In South America in particular, dengue is very prevalent, and many people when they see symptoms of a hemorrhagic fever will always think of dengue before anything else," said Maria Morales-Betoulle, a Centers for Disease Control and Prevention (CDC) researcher who worked on the 2019 Chapere outbreak. "It's similar. Very similar."

But laboratory tests showed no trace of dengue virus in the samples. The researchers tested for other pathogens endemic to the region, like yellow fever and Machupo, another rare, deadly hemorrhagic disease. But those tests turned up negative as well.

"They did not have a specific assay for Chapare virus," Morales-Betoulle told Live Science, referring to a method of identifying and studying a virus.

Morales-Betoulle's CDC lab had an ongoing partnership with the Latin America-focused Pan-American Health Organization (PAHO) to watch for emerging diseases.

"They reached out to us through PAHO, and they asked us, 'Would you accept these samples?'" she said. 

The bodily fluids arrived at the CDC, along with information about the outbreak.

"Even the description of the cases, in particular the [then-single known] fatal case among them … we decided to treat it as a viral hemorrhagic fever coming to our laboratory, handling it with the highest possible safety level." 

The researchers identified fragments of genetic material known as RNA from Chapare.

Details from the new outbreak showed the disease was now spreading from one person to another. The infected ambulance medic, for example, likely contracted the virus while resuscitating the medical resident as she was being transported to the hospital. (The medic survived; the resident did not.)

The CDC sent researchers into the region who worked with local experts. They found that the viral RNA was still present in the semen of one survivor 168 days after infection. They also found signs of the virus in rodents collected around the "home and nearby farmlands" of the first patient infected in the 2019 outbreak. (This doesn't yet prove that the rodents were the source of the outbreak. It's not even known whether rodents can infect people.)

The good news and the bad news

Morales-Betoulle and Carlson both said that all of these potentially worrisome details are, to a certain extent, good news: They show global health authorities working together effectively to identify and trace an emerging disease.

New viruses, including deadly viruses, are a fact of life in the 21st century.

"It's getting more common," to see new, potentially infection diseases emerge, Carlson said. "The ballpark used to be that there are about two or so emerging viruses every year. Things we've never seen before that we're seeing for the first time. And usually most of those are dead ends."

The rate of new emerging diseases has clearly increased in the last decade or two, Carlson said, though it's difficult to put a precise number on the uptick.

New viruses often spill over to humans through animals. But just because a virus jumps from an animal to a person doesn't mean it's likely to jump to other people.

"Most viruses when they make the jump from wildlife are poorly adapted enough to humans that they don't just luck out right on the first try," he said.

In other words, a virus making the jump to human beings is unlikely to already have the traits necessary to thrive and infect other humans.

But viruses that circulate in animal populations with close proximity to humans — farm animals, for example, and rodents — have more opportunities to spread through human populations. And climate change and habitat destruction are changing how wild animals live, making wildlife sicker and altering the relationship between people and the natural world, Carlson said. That brings more people into contact with once-distant viruses. 

Scientists and the public tend to think of deadly hemorrhagic diseases as African or South Asian, Carlson said. But Chapare's case shows they can turn up anywhere in the world.

Related: Why do ticks spread so many diseases?

"The reality is hemorrhagic viruses are everywhere, the species that carry them are everywhere, and we haven't had a really big run in like this here," he said. "This makes you sit up and say 'Oh, this is usually the sort of thing we get 10 years before something bigger along these lines.'"

That 10 year figure is a rough approximation. But viruses that eventually become major infectious diseases tend to make a few forays into human populations over the course of decades before really catching on. 

SARS-CoV-1 first turned up in 2002, infecting thousands. MERS, a related, much deadlier virus, turned up in 2012, and has killed 866 of the 2,519 people known to have caught it according to the CDC. SARS-Cov-2, which turned up in 2019, is the cause of the current global pandemic. Ebola caused 24 outbreaks between its first known appearance in 1976 and 2012, killing 1,590 people, according to the World Health Organization. Then in 2013, a strain of Ebola spread widely across several countries, infecting 28,646 people and killing 11,323.

The good news, Carlson said, is that this research shows the world is getting better at spotting these outbreaks as they emerge. Ten years ago, he said, researchers would not know about a Chapare outbreak so soon after so few people were infected. Finding the RNA in the semen and the potential disease vector of the rodents, he said, is particularly impressive — and good news for future efforts to find and quash the embers of potential pandemics before they explode.

Even in Bolivia, Morales-Betoulle and Carlson said, people don't need to worry about a major, COVID-19-style Chapare outbreak in the near future. There are no known human cases right now, and hemorrhagic fevers — lacking the long asymptomatic periods of COVID-19 or the ability to spread through the air — do not spread as easily or widely.

There is a concern though, Carlson said, that the damaging effects of COVID-19 on health care systems, and on the health of global populations, makes humanity more susceptible to other viruses.

People can protect themselves though. Rodent-borne diseases are a risk all over the world, Morales-Betoulle said. She recommends people follow CDC guidelines, published here, on avoiding contact with the scurrying little disease vectors. Among the key steps: sealing up holes in and outside homes, setting traps for the creatures to cull their populations and cleaning up food sources and rodent nesting sites.

CDC researchers presented the news about Chapare at the annual meeting of the American Society of Tropical Medicine and Hygiene.

Originally published on Live Science.