PULLMAN, Wash. —
A recent study highlights that a hantavirus, linked to serious respiratory illness in humans, may be more prevalent in rodent populations across parts of the Pacific Northwest than previously thought. The focus of the research was the Palouse area of Washington and Idaho.
Researchers discovered that nearly 30% of the rodents examined showed signs of past infection with the Sin Nombre virus, and about 10% were found to be actively infected, indicating they could transmit the virus.
The investigation was spearheaded by scientists from Washington State University’s College of Veterinary Medicine and appeared in the CDC’s Emerging Infectious Diseases journal.
“We were taken aback by how common the virus was locally and how little was previously known about it in the Northwest,” said Stephanie Seifert, the study’s lead author. “We’re really just starting to grasp how broad and intricate this virus is among rodent populations in this region.”
The Sin Nombre virus causes hantavirus pulmonary syndrome, first identified in an outbreak back in 1993 in the Four Corners region of the U.S. Between 1993 and 2022, there were 864 reported cases in the United States, with a concerning 36% case-fatality rate. Of these cases, 109 occurred in Idaho, Oregon, and Washington.
Hantavirus recently drew attention due to an Andes virus outbreak on a cruise ship. While Andes is a different strain found in South America and is quite rare, it is notable for being the only hantavirus that can spread from person to person.
The Sin Nombre virus primarily resides in deer mice, often found around farms, homes, and other structures. While rodents can transmit the virus among themselves through direct contact, human infections generally happen when individuals inhale particles from contaminated droppings, urine, or nesting materials.
This study involved fieldwork in the summer of 2023, as researchers captured rodents across farms and natural habitats in Whitman County, Washington, and in Idaho’s Latah and Benewah counties. They collected samples from 189 rodents, including deer mice, voles, and chipmunks.
In laboratory analysis, researchers found signs of both active infections and antibodies indicating past infections in deer mice and voles, which suggests potential virus transmission between species.
The team also obtained the first complete genome sequences of Sin Nombre virus strains from the Northwest, revealing significant genetic diversity and instances of viral reassortment. This genetic data may assist public health officials and scientists in tracking the virus’s evolution, pinpointing infection sources, and enhancing surveillance efforts.
Even with the notable prevalence of the virus in rodents, human infections remain rare. Researchers indicated that this might mean some infections go undetected. They expressed a desire to broaden their investigation if further funding is secured, which could include understanding how often people are exposed and how behaviors might affect risk.
“People might be encountering this virus more than we think, but severe cases tend to get more testing for hantavirus,” noted Pilar Fernandez, a co-author and disease ecologist at the Allen School. “Figuring out that connection—how exposure translates into illness—is the next major challenge.”
Health authorities advise taking precautions when cleaning areas where rodents may have been. Activities that disturb droppings or nests can elevate exposure risks by releasing virus particles into the air. Thus, sweeping or using equipment like leaf blowers can be especially risky in enclosed places. Proper ventilation and adopting wet-cleaning methods can help minimize inhalation risks.
