Fresno, Calif. •At least six rangers staffed phones this week at Yosemite National Park as visitors frightened about a growing outbreak of a deadly mouse-borne virus flooded lines seeking answers.

More than 1,000 calls a day are coming into the park, many from visitors wondering if they're in danger of contracting or being exposed to hantavirus pulmonary syndrome, park spokesman Scott Gediman said.

"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," Gediman 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. Two of those people have died from the illness that can cause acute respiratory and organ failure.

As the busy Labor Day weekend launches, some guests also are cancelling lodging reservations at the park. But Gediman says others on waiting lists for hard-to-get accommodations are snapping them up.

All six people who have contracted hantavirus stayed in "Signature" tent cabins in the park's historic Curry Village in Yosemite Valley, state health officials confirmed Friday. They were there between mid-June and early July.

The infections spurred park officials to close 91 of the Signature cabins.

Park officials 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 feces, urine and saliva of deer mice and other rodents.

The illness begins as flu-like symptoms but can quickly affect the lungs. It can take up to six weeks to incubate.

Warnings have gone out to visitors who stayed in Curry Village in June, July or August.

The hantavirus outbreak occurred despite park officials' efforts in April 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."

In 2009, the park installed the 91 new, higher-end cabins 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.

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.

The park has sent warning emails and letters to almost 3,000 people who stayed in tent cabins telling them they might have been exposed. The warning says anyone with flu-like symptoms or respiratory problems should seek immediate medical attention.

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 Centers for Disease Control. —

Basics about hantavirus outbreak

Answers to common questions about mice and the hantavirus linked to death of 2 people who visited Yosemite National Park:

How common is hantavirus pulmonary syndrome? • Up to 20 percent of all deer mice carry the virus, though levels can be higher. The illness is rare. Through 2011, there have been 587 documented cases since the illness was first identified in 1993.

How is it spread? • The most prolific carrier is the deer mouse, which prefers woodlands and high elevations, and can be found in desert areas. The virus in the saliva, feces and urine of infected mice is spread to humans who inhale airborne dust and aerosol particles. Symptoms develop in one to six weeks.

How do you tell a deer mouse from other mice? • House mice have solid colors, but deer mice range from gray to reddish brown, with white on their underbellies and sides of their tails.

Who is most susceptible? • Unlike the West Nile Virus, which is particularly hard on the elderly and people with compromised immune systems, there is no standard risk factor for humans when it comes to the hantavirus. Among the known cases, 63 percent have been men and 37 percent women. The range of ages was 6 to 83.

Can I catch it from someone who is sick? • Probably not. There have been no documented cases of hantavirus being spread by human to human contact.

What is the mortality rate? • More than 36 percent of people stricken with hantavirus have died from it. In 2011, half of the 24 people who got it died.

What are the signs? • It begins with chills, fever and muscle aches then progresses into a dry cough, headache, nausea and vomiting, then shortness of breath. People with hantavirus are put in intensive care, placed on oxygen and given medicine to prevent kidney failure.

How can I avoid exposure? • Open buildings that have been closed for a period of time and let them air out for 30 minutes. Spray mouse droppings with a water and bleach mixture, wait 15 minutes and mop up or wipe with paper towels.

Will I get it if I go to Yosemite National Park? • The chances are slim. More than 4 million people visit the park each year. Since 2000 there have been six suspected and confirmed cases.

The Associated Press