Hantavirus is spreading across parts of the US Northwest, with researchers reporting unusually high levels of the lung-damaging Sin Nombre virus in rodents across Washington and Idaho, according to the journal Emerging Infectious Diseases.
The findings published on 24 May in the journal, drawn from fieldwork in the Palouse region, suggest the virus is more entrenched in local wildlife than previously documented, raising concerns about human exposure in nearby farming communities.
Hantavirus has long been considered rare in the United States, with most cases linked to isolated exposure events rather than sustained regional presence.
The latest data arrives as health authorities continue to monitor passengers from a separate hantavirus-linked cruise ship incident involving a different strain, underscoring renewed scrutiny of how these viruses circulate and reach humans.
Levels In The Northwest Raise New Questions
The research team from Washington State University's College of Veterinary Medicine analysed 189 small mammals, including deer mice, voles and chipmunks, collected during the summer of 2023. What they found disrupted assumptions about the region.
Nearly 30 per cent of the rodents tested showed evidence of past infection with the Sin Nombre virus, while 10 per cent were actively infected at the time of sampling. Both farm and forest environments yielded similar results, indicating that the virus is not confined to remote or less-populated landscapes.
Study author Stephanie Seifert acknowledged the scale of the findings in a statement, noting the team had not expected such widespread presence or such limited existing data for the Northwest. She said researchers are only beginning to grasp how complex and geographically embedded the virus appears to be in local rodent populations.
The Sin Nombre virus is the primary strain responsible for hantavirus pulmonary syndrome in the US, a condition that begins with flu-like symptoms but can escalate rapidly. Patients may develop severe breathing difficulties as fluid builds in the lungs, placing strain on both the respiratory and cardiovascular systems. While still uncommon, the illness carries a high risk of serious complications.
Despite the elevated rodent infection rates, there is no indication that Sin Nombre spreads between humans. This distinguishes it from the Andes virus, a rarer strain associated with person-to-person transmission and recently linked to cases aboard a cruise vessel.
Transmission Risks And Public Health Advice
Transmission to humans typically occurs through inhalation of particles contaminated with rodent urine, droppings or saliva. That mechanism places certain everyday activities under renewed scrutiny, particularly in rural and agricultural settings where human and rodent habitats intersect.
Dr Sonja Bartolome, a pulmonary and critical care specialist at UT Southwestern Medical Centre who was not involved in the study, stressed that exposure risk is closely tied to behaviour. Speaking to Fox Digital News, she pointed to common cleaning practices as a potential hazard. Disturbing rodent waste by sweeping or using leaf blowers can release viral particles into the air, increasing the likelihood of inhalation.
Health guidance instead recommends wet-cleaning methods, which minimise airborne spread. The advice is not new, but the latest findings lend it sharper urgency, especially in areas where rodent infection appears sustained rather than sporadic.
Historically, hantavirus cases in the US have remained limited. Between 1993, when Sin Nombre was first identified in the Four Corners region, and 2022, a total of 864 cases were reported nationwide. Of those, 109 occurred in Idaho, Oregon and Washington combined. The new data do not suggest an immediate surge in human infections, but they do complicate the understanding of where and how risk accumulates.
Researchers argue that more comprehensive monitoring is now needed, particularly in agricultural zones where human exposure is more likely.
The study also highlights gaps in understanding how frequently people encounter the virus and how everyday behaviours influence that risk.
What remains uncertain is whether these elevated infection rates in rodents will translate into increased human cases. That link has not been established, and experts caution against drawing direct conclusions without further surveillance and epidemiological data.
