This little rodent is at the center of theories about the hantavirus epidemic

Andean virus, a type of hantavirushas sparked global concern in recent weeks after causing the death of three passengers and sickening at least eight others on board the MV. Hondiusa cruise ship traveling from Argentina across the Atlantic. We still do not know how or where the the epidemic began. But some health officials point the finger at a tiny South American rodent: the long-tailed pygmy rice rat, a common host of the Andean virus.

According to one estimate, almost 10 percent long-tailed pygmy rice rats in some areas carry the pathogen. The Andes virus spreads widely to humans who breathe in viral particles found in the feces, urine and saliva of rodents, and is the only hantavirus known to to transmit between people.

Although American officials point out that the risk to the public is low at present, the Andes virus has raised alarm in part because of its high mortality rate: hantavirus pulmonary syndrome (HPS), an illness caused by hantaviruses, can be fatal in up to 50 percent of cases, according to the World Health Organization (WHO).

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To help determine the exact origin of this particular outbreak, authorities plan to analyze hantavirus genome sequences found in rodents in South America to understand how the virus circulates – which will also help prevent “spillover” in the future, epidemiologist Maria Van Kerkhove said at a WHO news conference on Friday. The authorities suspect that known for the first time Those infected in the current outbreak – a Dutch couple on the cruise who died in April after falling ill – may have been exposed to the Andean virus in areas where the rat lives in South America.

Experts who study hantaviruses say the episode highlights how little we know about how these pathogens circulate in nature and why more research is needed to prevent an outbreak before it starts. “Most of the studies you’ll see in the literature are reactive. Once there’s an outbreak, people try to study what’s going on,” says Luis Escobar, associate professor in the Department of Fish and Wildlife Conservation at Virginia Tech. “We need more research to understand hantavirus in nature.”

There are, however, some things that scientists know about the long-tailed pygmy rice rat, or Oligoryzomys longicaudatus. It’s much smaller than the rats you might see running around the streets of New York, for example: Its body is often a little larger than the size of an AAA battery, Escobar says, although it could be bigger. The species is also an “ecological generalist,” meaning it can thrive in forests as well as grasslands, and can even live near homes in rural areas. “It shows tolerance to different habitats,” he says.

Although the rodent appears to be the main “reservoir” of the Andes virus (meaning it is most prevalent in this species), other rodents in South America can also contract it. In a 2018 studyFor example, Escobar and colleagues have identified other rodent species in Chile and Argentina that may carry Andean hantavirus and may pose a risk to humans, including the southern big-eared mouse, long-haired mouse, and olive tree mouse. It is not entirely clear why the long-tailed pygmy rice rat is such a good host; Researchers don’t know if it has to do with the rats’ behavior, biology or something else, he says.

The relationship between the virus and the host is a “co-evolutionary process,” explains Fernando Torres Perez, professor at the Institute of Biology at the Pontifical Catholic University of Valparaíso, Chile. “The virus has been present in the host population for some time” – probably thousands of years, he says – and it doesn’t appear to make the rats sick. (It is interesting to note that hamsters infected with Andes virus can develop a version of hantavirus pulmonary syndrome.)

This development is also underway: As climate change warms the planet and humans encroach further into wild spaces, researchers fear it will lead to more climate change. human-rodent overlapsuch as at higher altitudes or in areas likely to receive greater precipitation. In South America, for example, periods of heavy rainfall can create “booms” of populations of rodents called “ratadas” which have been destroyed. related to hantavirus outbreaks, says Torres Perez.

“We know that [climate change] This is going to have an impact on rodent populations,” explains Torres Perez. “One of these impacts could be the closer populations and increased contact with humans.”

All the more reason to track and study the rodent-virus dynamic now, says Escobar. “If we only conduct research after outbreaks occur, we fail to determine the baseline that tells us how the virus was in nature. »

“This is why we need this baseline: to understand [the] the necessary ingredients for these fallout events to occur in the first place.