Some South American rodent-borne viruses may spread as climate warms

Rodents in South America may be poised to carry disease to new places.

Warming temperatures and shifts in rainfall patterns could push some South American rodents to settle in new regions. Such shifts in suitable habitat may raise the risk that rodents infected with a group of deadly hemorrhagic viruses called arenavirus could spark a deadly outbreak among people in areas not previously in the line of fire, researchers report April 15 in npj Viruses. 

“That’s the worrying part,” says Pranav Kulkarni, a veterinary epidemiologist at the University of California, Davis’s Weill School of Veterinary Medicine. “These diseases are not on the public health officials’ radar.”

One rodent-transmitted virus is currently making headlines: Andes virus, a type of hantavirus, has sickened several passengers aboard a cruise ship that began its voyage in Argentina. Some patients have died. 

But hantaviruses are just one of many pathogens that rodents can transmit to people. Arenaviruses — a family that includes the virus that causes Lassa fever in parts of Africa — are another. These viruses can trigger severe hemorrhagic fevers with mortality rates ranging from 5 to 30 percent. 

Among the arenaviruses that have caused sporadic outbreaks across South America are Guanarito virus, Junin virus and Machupo virus. There are no approved treatments. A vaccine for Junin virus that may also provide some protection against Machupo virus is licensed in Argentina.

Farmworkers working in areas with infected rodents are typically at highest risk, Kulkarni says. But as Earth’s climate changes, the critters could move to new areas, bringing the viruses with them. “If there is going to be a high-impact outbreak of arenaviruses,” Kulkarni says, “these might be the candidates.” 

Kulkarni and colleagues ran computer simulations incorporating habitat suitability for six rodent species known to carry one of the three viruses. The calculations also took future climate projections and population density into account. The team found that the risk of viral transmission from rodents to people goes up over the next 20 years in parts of the continent that aren’t currently at risk.

Guanarito virus, for instance, is currently found in central Venezuela. But by 2060, the virus could spread to parts of Colombia, Guyana, Suriname and Brazil. Junin virus risk could move from grasslands in Argentina to other parts of the country as well as Paraguay and Bolivia. And Machupo virus, currently found in Bolivia, could in the future also infect people in Brazil, Paraguay and Peru. 

The resulting risk maps “set the stage,” says Greg Glass, a disease ecologist at the University of Florida in Gainesville, who was not involved with the work. “It allows folks going forward to use these maps to set up studies to go see if these species are there or not.” 

For Glass, verifying the current maps should be the next step. It’s possible the simulations suggest circulation in regions where rodents aren’t truly carrying the viruses. But if the simulations “say it shouldn’t be there, but you find it … that’s a bigger mistake” that could cost lives, he says.

Temperature shifts and changes in precipitation were among the climate factors driving shifts in rodent populations in the simulations. Human activities such as agriculture and urbanization also played a role. But the simulations focused on long-term changes, Kulkarni says. “What we would really like to do is look at short-term changes in weather, short-term changes in certain climate disruptions and how that affects risk from week to week or month to month.”

Some changes could already be happening. Hantavirus cases are on the rise in Argentina, said Carlos del Rio, a virologist and infectious diseases physician at Emory University in Atlanta, during a May 7 news briefing. “The main cause of that is climate change. Argentina is becoming more tropical.” 

Some of the rodents included in the study can also transmit hantaviruses, Kulkarni says. The yellow pygmy rice rat (Oligoryzomys flavescens), for instance, transmits not only Junin virus but also some hantavirus strains. Although the yellow pygmy rice rat is not a known reservoir of the Andes hantavirus strain that is responsible for the cruise ship outbreak, it’s possible that other rodents and pathogens will also expand their ranges as the climate changes.

“Climate change is a reality,” del Rio said. “And it has a significant impact in infectious diseases.”