FRESNO, Calif. (AP) -- Two more Yosemite National Park visitors have been found with a mouse-borne virus blamed for the deaths of two people, bringing the total number of infections to six, state health officials said.

The new discoveries were made during the agency's investigation into cases of hantavirus pulmonary syndrome at the famed park, California Department of Public Health Anita Gore spokeswoman said.

The infections spurred park officials to close 91 tent cabins at Curry Village in Yosemite Valley, where five of the six infections occurred. Gore said one of the infected people may have been in another area of the park.

"Our investigation is trying to determine which area of the park that person visited," she said.

Over the past three weeks, two people have died of hantavirus pulmonary syndrome after staying in cabins at Curry Village in Yosemite Valley.

Park officials said the double-walled design of the cabins that were closed Tuesday made it easy for mice to nest between the walls. The disease is carried in 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.

Five of the people who fell ill are known to have stayed in the tent cabins in June or July, and warnings have gone out to visitors who stayed in Curry Village in June, July or August.

The hantavirus outbreak occurred despite efforts by park officials to step up protection efforts last April. 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 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."

It came after the state report revealed that 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.

In 2009, the park installed the 91 new, higher-end cabins 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.

The new cabins have canvas exteriors and drywall or plywood inside, with insulation in between. Park officials found this week when they tried to shore up some of the cabins that mice had built nests in the walls.

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.

The park sent warning emails and letters Wednesday to another 1,000 people who stayed in tent cabins, after officials found that a computer glitch had stopped the notices from going out with the original 1,700 warnings Monday. The warning says anyone with flu-like symptoms or respiratory problems should seek immediate medical attention.

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.

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