Up to 10,000 Yosemite visitors at risk of virus

A 2010 report from the state health department warned park officials that rodent inspection efforts should be increased after a visitor to the Tuolumne Meadows area of the park fell ill.

The report revealed 18 percent of mice trapped for testing at various locations around the park were positive for hantavirus.

“Inspections for rodent infestations and appropriate exclusion efforts, particularly for buildings where people sleep, should be enhanced,” it said.

The park’s new hantavirus policy, enacted April 25, was designed to provide a safe place, “free from recognized hazards that may cause serious physical harm or death.”

The 91 insulated, high-end canvas cabins in the century-old Curry Village are new to the park. They were constructed in 2009 to replace some that had been closed or damaged after parts of Curry Village, which sits below the 3,000-foot Glacier Point promontory, were determined to be in a rock-fall hazard zone.

Upon taking them apart for cleaning, park employees found evidence of mouse nests in the insulation.

The deer mice most prone to carrying the virus can squeeze through holes just one-quarter-inch in diameter. They are distinguished from solid-colored house mice by their white bellies and gray and brown bodies.

In 2011, half of the 24 U.S. hantavirus cases ended in death. But since 1993, when the virus first was identified, the average death rate is 36 percent, according to the CDC.

• Jason Dearen reported from San Francisco

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