Ever since 1993, when a deadly disease outbreak in the Four Corners first revealed the presence of hantavirus in North America, New Mexicans have been warned to be on the lookout for deer mice, which harbor the microbe and can spread it through their droppings.
A few human cases, usually presenting with severe cardiopulmonary symptoms, typically occur in New Mexico each year – almost all in the northwestern quadrant of the state – and even with advanced treatment about 35 percent of patients die.
But now, University of New Mexico researchers have found that more than 30 species of rodent and other small mammals endemic to the Southwest actually carry the virus, including ground squirrels, chipmunks, gophers, rats and even house mice.
In a study published in PLOS Pathogens , a team led by Steven Bradfute, PhD, an associate professor in the Center for Global Health within the UNM School of Medicine's Department of Internal Medicine, reported that genomic material from the sin nombre virus – the prevalent hantavirus strain in the U.S. – was present in about a quarter of the more than 1,500 small mammals collected throughout New Mexico between 2019 and 2023.
The most likely way people get infected is when they breathe in aerosolized droppings excreted by the animals, he said. To determine whether species other than deer mice might spread the disease, the team was able to isolate live hantavirus from their salivary glands and lung tissue.
"There's a lot of deer mice, and they carry the virus, but there's a lot of other rodents that also carry the virus and they can shed live virus," Bradfute said. "So, they're very much potential vectors as well."
One puzzle yet to be solved, he said, is why the reported human hantavirus cases in New Mexico remain concentrated in the Four Corners region, even though mammals elsewhere in the state have now been shown to carry the live virus.
"One possibility is the genetic sequence of the virus is different in the northwest, versus the southeast," Bradfute said. 'We are in the middle of testing that, although the hantaviruses are notoriously difficult to sequence. Our preliminary results don't suggest there's a huge difference between the different regions, but we still need to wait for the full sequence to be completed."
Another possibility is that there are cases in southeastern New Mexico, but they're just not being recognized, he said. "We are looking at that question by looking at antibodies in humans from different regions. We've just started a project with that, but we don't have the data yet."
In addition, there could be something about the viral transmission from rodents to humans that is more efficient in northwestern New Mexico than in the southeast, Bradfute said.
"That could be due to how well the particles are aerosolized and how stable the virus is. I think that's plausible because it is geographically quite different in those two areas."
It could also be the case that rodents simply carry higher levels of the virus in the northwest versus the southeast, he said. "We've started looking at that, and what we do see is in the regions where there are recorded cases, there are some animals that have really high viral loads."
Hantavirus drew international headlines recently when it was determined to have caused the death of Betsy Arakawa, wife of actor Gene Hackman, in their Santa Fe home. The tragedy underscores the need to take precautions when entering enclosed or unventilated spaces, especially in the spring and summer months as small mammals multiply, Bradfute said.
"The incubation period from the time you get exposed to the time you have symptoms is typically at least one or two weeks and could be as long as eight weeks," he said. Early symptoms mimic the flu or COVID, but after a few days, it's not uncommon to develop severe shortness of breath and extreme exhaustion. "That's when you're in a danger zone," Bradfute said.
In the absence of any effective antiviral drugs, medical treatment mainly consists of trying to manage disease symptoms, he said. Sicker patients are often placed on extracorporeal membrane oxygenation (ECMO) machines that take over from the heart and lungs to give the body time to fight off the infection. Bradfute and his colleagues are part of an effort to develop monoclonal antibody treatments, which so far have proved to be protective in animal models.
For now, the best strategy is to avoid becoming infected in the first place, he said. People who come across rodent droppings should wear a well-fitting N95 or KN-95 mask and gloves and spray the droppings with a 10% bleach solution while thoroughly ventilating the affected area. "When you clean up, you should use paper towels and don't do things that generate aerosols, like sweeping or using a vacuum."
The good news is that, unlike SARS-CoV-2, the sin nombre hantavirus is not spread from person to person, and it doesn't survive long in open air or when exposed to sunlight.
"What I try to tell people is it's good to be careful, but don't worry too much about things," Bradfute said. "Take precautions when you can, but fortunately, the transmission as of now is pretty rare."
