Two people have died of the rare rodent-borne hantavirus after visiting Yosemite national park this summer. Officials from California's famed nature spot are warning past visitors to be aware of some flu-like aches and symptoms as fears rise of a possible outbreak.

Health officials learned at the weekend that hantavirus had killed a second person, who had visited the park in June, spokesman Scott Gediman said. There is one other confirmed case of the illness and a fourth is being investigated.

US federal health workers said symptoms may develop up to five weeks after exposure to the urine, droppings or saliva of infected rodents. There is no specific treatment for the virus and about one third of people who contract it will die.

after the first death anyone with symptoms was advised to seek medical attention and let doctors know if they had been camping in Yosemite. They said that because thousands of people visit the park every month it would be impossible to track everyone who had been in Curry Village, where it is suspected the victims caught the virus.

Park officials said visitors who stayed in tent cabins there between mid-June and the end of August should beware of fever, aches, dizziness and chills.

Curry Village, a group of rustic cabins at the base of the 900 metre (3,000ft) promontory Glacier Point, is the most popular and economical lodging area in the park. Gediman said contractors were working on the cabins to protect park visitors.

"This was never because the cabins were dirty, it was never because we didn't take care of them. This is just because approximately 20% of all deer mice are infected with hantavirus. And they're here in Yosemite Valley," he said.

These are the first such deaths among park visitors, although two other people caught the virus in a more remote area in 2000 and 2010, officials said.