Park officials said the double-walled design of the 91 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.
Over the past three weeks, two people have died of hantavirus pulmonary syndrome after staying in one of the so-called "Signature" cabins of Curry Village. Another person is confirmed ill and one more likely has the virus that kills 36 percent of the people it infects.
Mike Gauthier, Yosemite chief of staff, said the design allowed for rodent infestation.
"We just weren't aware that design would lead to it," he said.
A report obtained earlier in the day said the National Park Service was warned in 2010 that efforts should be stepped up to inspect for rodents in Yosemite and prevent them from entering areas where people sleep.
The 2010 report issued by the California Department of Public Health was commissioned by the park service.
"Inspections for rodent infestations and appropriate exclusion efforts, particularly for buildings were people sleep, should be enhanced," it said.
"We worked with Yosemite to evaluate risk and make recommendations to reduce the possibility of transmission to people," added said Vicki Kramer, chief of the vector borne disease section of the health department. "That included reducing the number of mice, and excluding them from structures."
This past spring the department gave Yosemite a cleanup plan, Kramer said, similarly outlining how to appropriately deal with mouse excrement.
"Yosemite, to their credit, has taken quite a few steps to address this," she said. "But it's a wilderness area and these buildings aren't going to be tight. It's impossible to get rid of the deer mice, so there is going to be some risk to being in a wilderness area."
Further details were not immediately available. The health department said it was preparing a statement.
The report was commissioned after two park visitors fell ill after staying in Tuolumne Meadows, about 4,000 feet higher than Yosemite Valley. It said that 18 percent of mice trapped for testing at various locations around the park were positive for hantavirus.
"The identification of the second case ... underscores the ongoing risk and need for dutiful adherence to a rodent exclusion and control program," the report said.
Gauthier said he had not yet seen the report.
Meanwhile, public health workers sent 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 to people entering park gates.
Officials sent emails and letters on Wednesday to another 1,000 people who stayed in tent cabins in Curry Village. That was in addition to 1,700 Curry Village guests who had previously been sent such warnings.
The rustic tent cabins of historic Curry Village are a favorite among families looking to rough it in one of the nation's most majestic settings.
Park employees removing insulation have found mouse nests and droppings in some of the 91 so-called Signature cabins they had been attempting to shore up to make entry more difficult.
The deer mice most prone to carrying hantavirus pulmonary syndrome can squeeze through holes just one-quarter-inch in diameter.
The guests being warned stayed in Curry Village's tent cabins in June, July or August. So far all victims who have fallen ill stayed in the cabins in June.
The illness begins as flu-like symptoms but can quickly affected the lungs. It can take up to six weeks to incubate.
In issuing the new warnings it was unclear whether authorities expanded the boundary of potential exposure or extended the dates.
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. Most often they are isolated, so having this cluster of cases from a small area in Yosemite has perplexed public health officials.
The federal government has two epidemiologists working in the park. They are trapping mice and rodents in an effort to determine how much of the population carries the virus and to see whether there are more mice in Yosemite Valley this year than in other years.
Deer mice are distinguished from solid-colored house mice by their white bellies and gray and brown bodies.
Kramer warned people never to sweep or vacuum mouse droppings. Instead spray them with a mixture of bleach and water then wipe it up with paper towels or a mop.
