Study: 10% Pacific Northwest rodents carry hantavirus

Washington State University researchers said on May 21 that a hantavirus linked to severe human respiratory disease may be more widespread in parts of the Pacific Northwest than previously recognized. The study, published in the CDC’s *Emerging Infectious Diseases* journal, found that nearly 30% of rodents sampled in the Palouse region of Washington and Idaho showed evidence of past infection with Sin Nombre virus, and about 10% were actively infected. KTVZ reported the findings on May 23, citing concern about possible human exposure in the region, including eastern Washington. ### Which virus did researchers find in the rodents? Sin Nombre virus is the hantavirus at issue in the study, and it is the strain most commonly associated with hantavirus pulmonary syndrome in the United States. Washington State University said the virus can cause a severe respiratory disease in humans and is primarily maintained in deer mice, which are common around farms, homes and outbuildings. (news.wsu.edu) The CDC says hantavirus pulmonary syndrome is a severe and potentially deadly lung disease. From 1993 through 2022, 864 U.S. cases were reported, with a 36% case-fatality rate, according to the CDC journal article and the WSU release; 109 of those cases were in Idaho, Oregon and Washington. ### Where were the rodents sampled? Field work took place in the summer of 2023 in Whitman County, Washington, and Latah and Benewah counties in Idaho, according to Washington State University. (news.wsu.edu) The study focused on the Palouse, an agricultural region that spans eastern Washington and north-central Idaho. KTVZ and other regional outlets described the findings as relevant to eastern Washington because Whitman County was among the sampling areas. (wwwnc.cdc.gov) The WSU release said researchers trapped rodents across farms and natural areas during the field work. ### What does the 10% figure actually mean? About 10% of the rodents were actively infected, meaning they were carrying the virus and could potentially shed it into the environment, Washington State University said. (news.wsu.edu) A separate 30% figure reflected evidence of past infection, based on antibodies, not current shedding. Stephanie Seifert, the study’s corresponding author and principal investigator of the Molecular Ecology of Zoonotic and Animal Pathogens lab in WSU’s Paul G. (ktvz.com) Allen School for Global Health, said in the university release that researchers were surprised “both by how common the virus was locally and by how little data existed for the Northwest.” (news.wsu.edu) ### How do people get exposed? Human infections typically occur when people inhale airborne particles from contaminated rodent droppings, urine or nesting materials, Washington State University said. The CDC says people should avoid contact with rodent urine, droppings, saliva and nesting materials, and that rodent control is the primary strategy for prevention. (news.wsu.edu) The CDC and Washington health officials say activities that stir up dust can raise the risk of exposure. They recommend ventilating enclosed spaces before cleanup and using wet-cleaning methods rather than sweeping, vacuuming or using leaf blowers on contaminated material. ### What should hikers, campers and homeowners do now? The CDC says the practical advice is to limit contact with rodents and clean infested spaces carefully. (news.wsu.edu) That means sealing entry points, controlling rodents near homes and sheds, and treating droppings and nests as potentially infectious rather than sweeping them dry. CDC guidance also says symptoms can begin one to eight weeks after contact with an infected rodent and can start with fever, fatigue and muscle aches before progressing to coughing and shortness of breath. (cdc.gov) The agency says clinicians should consider hantavirus testing when compatible symptoms follow rodent exposure. ### Where can readers find the underlying study? The findings were published in the CDC’s *Emerging Infectious Diseases* journal in May 2026, and Washington State University identified the paper as a study of Sin Nombre virus sequences and prevalence in the northwestern United States. (cdc.gov) The WSU release and CDC journal page were both live as of May 24, 2026. (wwwnc.cdc.gov) (cdc.gov)