The rustic tent cabins of Yosemite National Park in California have become the scene of a public health crisis after two visitors died from a rodent-borne disease following overnight stays.

On Tuesday, park officials sent letters and emails to 1,700 visitors who stayed in some of the dwellings in June, July and August, warning them that they may have been exposed to the disease that also caused two other people to fall ill.

Deer mice are the main reservoir for the virus that causes hantavirus cardiopulmonary syndrome, which four visitors to Yosemite National Park have contracted, officials say. (Courtesy CDC)

Those four people contracted hantavirus pulmonary syndrome after spending time in one of the 91 "Signature Tent Cabins" at Curry Village around the same time in June. The illness is spread by contact with rodent feces, urine and saliva, or by inhaling exposed airborne particles.

After the first death, the park sanitized the cabins and alerted the public through the media that the cause might have been diseased mice in the park.

However, officials did not know for sure the death was linked to Yosemite or the campsite until the U.S. Centers for Disease Control determined over the weekend that a second visitor, a resident of Pennsylvania, also had died.

Watching for illnesses

After every park tragedy, officials stress that Yosemite is a wilderness area and with it come some dangers.

"We're very concerned about visitors and employees," park spokesman Scott Gediman said. "But we feel we are taking proactive steps in both cleaning the affected areas and in public education. But it's absolutely impossible to eliminate all risk."

On Sunday night, health officials with the National Park Service sent out an alert asking public health authorities to be on the watch for more potential rodent-related cases of acute respiratory failure.

Yosemite receives 4 million tourists a year from around the world, and national park officials were trying to determine if the warning should be expanded to include foreign countries.

The disease can incubate for up to six weeks before flu-like symptoms develop. It's fatal in 30 per cent of all cases, and there is no specific treatment. It is not spread human-to-human.

All the victims stayed in the cabins between June 10 and June 20, and all four known cases were contracted by people who stayed within 30 metres of each other but not necessarily in the same cabins.

A 37-year-old man from the San Francisco Bay area was the first person to die. Further details have not been released because of medical privacy laws.

Of the 587 documented U.S. cases since the virus was identified in 1993, about one-third proved fatal.

Deer mice were determined to be the main carriers of the virus, though other rodents can be infected, according to the CDC. Most of the cases occur in the West, though researchers are not sure why.

This year's deaths mark the first such fatalities of park visitors, although two others were stricken in a more remote area of the park in 2000 and 2010.