Up to 10,000 people who stayed in lodging cabins at Yosemite National Park may have been exposed to a deadly mouse-borne virus that has killed two people.
Park concessionaire Delaware North sent letters and emails this week to nearly 3,000 people who reserved the insulated Signature cabins 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 could mean up to 7,000 more visitors might have been exposed to the virus that so far has killed two people and made four others ill.
Meanwhile, more than 1,000 calls a day are coming into the national park as visitors frightened about the growing outbreak hantavirus pulmonary syndrome call seeking answers.
On Thursday the California Department of Public Health confirmed that a total of six people had 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 Centres for Disease Control and Prevention.
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 admitted to hospital. More than 36% of people who contract the rare illness will die from it.
All of the victims confirmed so far stayed in the plush Signature tent cabins in the California park's historic Curry Village section between mid-June and early July. Park chiefs said the double-walled design of those particular cabins made it easy for mice to nest between the walls. The disease is carried in the faeces, urine and saliva of deer mice and other rodents and carried on airborne aerosol particles and dust.
The 91 insulated canvas cabins in the century-old Curry Village are new to the park, built in 2009 to replace some that had been closed or damaged after parts of Curry Village, which sits below the 3,000ft Glacier Point promontory, were determined to be in a rock-fall hazard zone. Park staff found evidence of mouse nests in the insulation while taking them apart for cleaning.
In 2011, half of the 24 US hantavirus cases ended in death. But since 1993, when the virus first was identified, the average death rate is 36%, according to the CDC.