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Yosemite Hantavirus Outbreak May Offer Clues To Rare Disease

California researchers and public health officials have launched what they describe as a groundbreaking series of studies of a rare mouse-borne virus that has infected at least nine Yosemite National Park visitors, killing three of them, since June.

Public health officials are also developing an unprecedented voluntary medical screening of the scenic park’s 2,500-plus employees.

Chiu already has begun performing genome sequencing of the virus using tissue samples taken from patients infected in this summer’s outbreak, as well as with tissue taken from rodents carrying the virus in Yosemite and throughout California.

Danielle Buttke, a National Park Service veterinary epidemiologist, said: “We want to take this opportunity to learn as much about the disease as we possibly can … I think there’s a lot to be learned here.”

Constant strain?
Chiu said his study will examine whether the virus that infected Yosemite visitors last summer is the same as the strain first identified in 1993, when a then-mysterious disease now known as hantavirus pulmonary syndrome struck 18 people in the U.S. Southwest.

“Is this a different strain, potentially a mutated virus? Has the virus evolved?” Chiu asked. “I actually don’t think so, but the only way to confirm that is to do the study.”

All but one of the Yosemite visitors who contracted the disease over the summer are believed to have been exposed in Yosemite’s Curry Village area while staying in double-walled tent cabins later found to have been infested by deer mice.

“We don’t know if it was a specific factor or a confluence of factors. So we’re looking at people, animals and the environment to understand the situation. When the health of the environment is poor, that’s often when you see infectious disease occur,” she said.