90-Second Read: A shocking number of Pacific Northwest rodents may carry Hantavirus

The research was conducted in the summer of 2023, predating the current Hantavirus outbreak, which began on a cruise ship in early May. But a disproportionate number of the total cases have been seen in the Pacific Northwest: Of the 864 cases in the United States between 1993 and 2022, 109 were in Idaho, Oregon or Washington, according to the study. That makes it hard to say if the number of rodents carrying the virus there has grown over the years, says Seifert. The number of rodent carriers were higher than previously suspected, says Stephanie Seifert, an assistant professor at Washington State University and co-author of a study published in April in Emerging Infectious Diseases.

The samples were tested for both Hantavirus antibodies, a sign of an active infection, and for viral RNA, which can indicate if the rodent has ever carried the virus. Sin Nombre is not transmissible from human to human, unlike the Andes virus at the center of the cruise ship outbreak. Human cases of Hantavirus are relatively rare in the U.S., with most cases occurring in the South West. Wetter winters can lead to increased vegetation, which in turn can support a larger rodent population.

The results showed around 10 percent had Sin Nombre at the time the samples were taken, while almost 30 percent showed signs of past infection. Instead, people become infected when they are exposed to rodents and their excretions, such as their feces and urine. Even so, few studies have examined how common the viruses are in the area's rodents. Still, climate change may play a role in the virus' spread, says Seifert.

The way humans use the land can also increase their exposure to the animals. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history. However, whether such a study will take place is an open question.