YOSEMITE NATIONAL PARK (CNN) -- Health officials said Wednesday that they've sent warnings to Yosemite National Park visitors from 39 other countries about a potentially deadly hantavirus uncovered at some of the park's cabins this summer.
The Centers for Disease Control and Prevention said up to 10,000 people were at risk, after estimating the number of friends and family members of those who stayed with visitors who booked reservations at the cabins.
"All guests who made reservations to stay in the 'Signature Tent Cabins' from June 10 through August 24, 2012 (approximately 2,900 persons) were e-mailed or mailed a health advisory urging them to seek immediate medical attention if they or other persons in their party exhibit symptoms of HPS," or hantavirus pulmonary syndrome, the CDC reported last week.
Six cases of hantavirus have been reported at Yosemite, the California Department of Public Health said last week. Two of those infected died.
The syndrome is a rare lung disease that kills about a third of those infected. Symptoms can include fever, chills, cough, headaches, gastrointestinal problems, muscle aches and fatigue, though it is not communicable from person to person.
The incubation period is typically two to four weeks after exposure, with a range of a few days up to six weeks. In the United States, the carriers of hantavirus are deer mice, cotton rats, rice rats and white-footed mice.
The virus can be present in the rodents' urine, droppings and saliva, and it is spread to people when they breathe in air contaminated with the virus, the CDC says.
Before this year, Yosemite National Park saw one hantavirus case each in 2000 and 2010. There is no specific treatment for a hantavirus infection, according to the CDC, but the earlier a patient is brought to intensive care, the better.