US park service was warned about Yosemite rodents

The disclosure came just days after a second Yosemite park guest was confirmed to have died of the rodent-borne hantavirus pulmonary syndrome. Both victims had stayed at the park's Curry Village.

Most hantavirus cases are isolated, so the Yosemite cluster has perplexed public health officials.

The 2010 report by the California Department of Public Health was commissioned by the park service after two visitors fell ill after staying elsewhere in the park.

The report says 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 says.

The chief of the department's vector-borne disease section, Vicki Kramer, said the department worked with Yosemite to make recommendations to reduce the possibility of transmission to people. "That included reducing the number of mice and excluding them from structures."

Officials with Yosemite National Park and public health officials with the National Park Service did not immediately return calls seeking comment.

Public health workers are now sending warnings to more people who visited Yosemite this summer, saying they could have been exposed to the deadly rodent-borne disease. They also handed out warnings at park entrances.

The disease can be transmitted by inhaling airborne particles of the feces, urine and saliva of deer mice and other rodents. The illness begins as flu-like symptoms but can quickly affect the lungs. It can take up to six weeks to incubate.

At least one other person has been sickened, and public health officials awaited tests on a fourth possible case.

So far, all victims stayed in the Curry Village cabins in June. The guests being warned stayed in the village's tent cabins in June, July or August.

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 36.39 percent, according to the Centers for Disease Control.

Most of the nearly 600 cases reported since 1993 have been in New Mexico, Colorado, Washington, Arizona and California.

The federal government has two epidemiologists working in Yosemite. They are trapping mice and rodents to determine how much of the population carries the virus and whether the park has more mice than in other years.

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