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Hantavirus in Yosemite: Doctors try to solve disease's mysteries

September 11, 2012 |  9:37 am

Yosemite hantavirus
This summer's hantavirus outbreak in Yosemite National Park has served as a sobering reminder that mystery still surrounds the disease, doctors say.

"The biggest mystery is we don't have a good explanation," said Barbara Knust, a Centers for Disease Control and Prevention epidemiologist. "For Yosemite, why this year of all years is there an increased number of cases?"

Nearly 20 years after being identified in the U.S., hantavirus is better understood but no less vexing. Researchers now know it causes hantavirus pulmonary syndrome, a severe respiratory disease. It is transmitted through the droppings and urine of deer mice, and not through person-to-person contact.

Treated early, patients have a better chance of survival. But there is no cure, and more than one-third of patients die. The Yosemite cases follow the pattern: Three of the eight visitors who fell ill died. Officials have called the outbreak unprecedented — more than one hantavirus infection from the same location in the same year is very rare.

The National Park Service has closed the cabins believed to be at the heart of the outbreak. State and federal scientists are scouring the park, trapping mice and conducting laboratory tests.

Public health officials are warning doctors worldwide to watch for possible symptoms, which can be confused with the flu and can take weeks to show up. And the California Department of Public Health said the risk of new cases remains, even as the summer surge of visitors wanes.

"These are not isolated cases in the hospitals in the mountains," said Daniel Uslan, assistant professor of infectious diseases at UCLA's medical school. "These are potentially people coming back to Los Angeles or other urban centers where doctors are perhaps not as aware of the infection."

Officials investigating the Yosemite cases have more to go on than a lucky tip. But they are under pressure to quickly learn more about a disease that is pervasive and deadly.

The CDC started tracking every case of hantavirus pulmonary syndrome across the U.S. in 1993, when 48 people became ill. From 1994 to 2011, an average of 28 people got the disease each year.

Yosemite may provide more clues in the long-running hantavirus mystery. Public health officials and epidemiologists are compiling information about the cases, hoping they can determine the deadly combination of factors that led to the outbreak.

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-- Kate Mather and Anna Gorman

Photo: Tents in Curry Village in Yosemite National Park, where the hantavirus disease has been found. Credit: Ben Margot / Associated Press.

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