(CBS/AP) FRESNO, Calif. - Yosemite park rangers said on Friday that up to 10,000 people who stayed in the national park may have been exposed to the rodent-borne hantavirus, which kills one-third of the people it infects.
Park concessionaire Delaware North Co. sent letters and emails this week to nearly 3,000 people worldwide who reserved the insulated "signature" cabins in Curry Village between June and August, warning them that they might have been exposed.
The cabins hold up to four people, and park spokesman Scott Gediman said Friday that means up to 7,000 more visitors might have been exposed to the virus that so far has killed two people and sickened four others.
Meanwhile, more than 1,000 calls a day are coming into Yosemite's new hantavirus hotline as visitors frightened about the growing outbreak of hantavirus pulmonary syndrome call seeking answers.
"We're reaching out and they are reaching out to us, and we are trying in every way shape and form to be transparent and forthright," he said. "We want to tell people this is what we know. The most important thing is the safety of park visitors and employees."
On Thursday, the California Department of Public Health confirmed that a total of six people have contracted the disease at Yosemite, up from four suspected cases earlier in the week.
Alerts sent to state and county public health agencies, as well as local doctors and hospitals, have turned up other suspected cases that have not yet been confirmed, according to the Centers for Disease Control and Prevention.
"Additional suspected cases are being investigated from multiple health jurisdictions," the CDC said in an advisory issued to health care providers.
The hantavirus causes Hantavirus Pulmonary Syndrome (HPS). The illness that begins as flu-like symptoms can take six weeks to incubate before rapid acute respiratory and organ failure. There is no cure, and anyone exhibiting the symptoms must be hospitalized.
All of the victims confirmed so far stayed in the high-end, insulated tent cabins in the Curry Village section between mid-June and early July.
Park officials worked quickly to disinfect all 400 of the Curry Village cabins when the outbreak first was detected earlier this month. When the outbreak was narrowed to the 91 double-walled insulated cabins, the California Department of Public Health ordered them shut down Tuesday.
Because the cabins are made up of two walls filled with insulation, park spokeswoman Kari Cobb to HealthPop said authorities are afraid that. Yosemite has moved all people who reservations at Curry Village to other accommodations in the park.
The disease is carried in the feces, urine and saliva of deer mice and other rodents and carried on airborne aerosol particles and dust.
As the busy Labor Day weekend launches and word about the outbreak spread, some guests were cancelling lodging reservations at the park. But Gediman says others on waiting lists for hard-to-get accommodations are snapping them up.
The hantavirus outbreak occurred despite park officials' efforts to step up protections.
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.