Everything you need to know about the Yosemite hantavirus outbreak

The hantavirus outbreak did little to quash the beauty of Yosemite, made
more beautiful on Labor Day weekend by lighter crowds.
The hantavirus outbreak did little to quash the beauty of Yosemite, made more beautiful on Labor Day weekend by lighter crowds.
Stephanie O'Neill/KPCC
The hantavirus outbreak did little to quash the beauty of Yosemite, made
more beautiful on Labor Day weekend by lighter crowds.
The deadly face of the Hantavirus. The little-known virus is spread through the deer mouse's droppings and urine.

EDITOR'S NOTE: The following FAQ on Yosemite's hantavirus outbreak was compiled through interviews with scientists from the National Park Service Office of Public Health and officials at Yosemite National Park; information from the National Park Service and the Health and Human Service Agency - State of California.

What is Hantavirus Pulmonary Syndrome (HPS)?

It’s a rare but often fatal disease of the lungs. HPS was first recognized in the U.S. in 1993 in the Four Corners region by a physician for the Navajo Nation, but scientific testing of stored serum samples now show a Utah resident was infected with the virus in 1959.

Is the disease unique to Yosemite National Park?

No. It’s found throughout the United States.

This outbreak has been called “unprecedented.” Why?

Until now, HPS has shown up in isolated cases. This is the nation’s first known “oubreak” of hantavirus.

Are there different types of hantavirus in the United States?

Yes. There are many types. But it’s the Sin Nombre virus (SNV) that causes HPS in the western United States.

How is it spread?

Through the droppings, urine and saliva of infected rodents that become airborne when disturbed.

What rodents carry it in California?

The deer mouse is the only rodent species known to carry hantavirus in the Golden State.

What does a deer mouse look like?

They’re about the same size as your typical house mouse (4 to 7 inches from nose to tail). But unlike the solid-colored house mice, deer mice are two-toned: white underneath and grey to brown on top. Infected rodents have been found nationwide. (See photo above.)

How do humans get infected with hantavirus?

The most common means of a human contracting HPS is by inhaling the virus in a poorly ventilated area contaminated by deer mouse urine, droppings or saliva. Scientists also believe you can become infected if you have the virus on your hands and then touch your mouth or eyes; or if you eat food contaminated with the urine or droppings of infected mice.

Can it be transmitted person-to-person?

No. And it also can’t be transmitted by cats, dogs, birds, insects or other animals, which scientists say don’t carry the virus.

What are the symptoms?

Hantavirus mimics common flu symptoms. Those infected may suffer headaches, fever, nausea and muscle aches – especially in the thighs, hips, back and shoulders.

How soon after infection do symptoms appear?

From between one to six weeks.

Is there a cure?

No. But early medical attention can increase the chance that you’ll survive, health officials say.

What is the fatality rate?

About 35 percent of those who get it die from it.

Should I cancel my trip to Yosemite?

Park officials and scientists believe it’s safe to visit the park both for day trips and overnight visits.

Why do health officials say it’s safe to visit Yosemite, especially as new cases keep arising?

Because the park has now closed the Curry Village “signature” tent cabins where all but one case so far appears to have originated. Any future cases are likely to have been contracted between June 10 to August 24, when the park indefinitely closed the signature tent cabins.

Why are the signature tent cabins the problem?

Public health officials are still studying the reasons but it’s believed the design of the signature tent cabins is a factor. The signature cabins have interior plywood and foam-insulated interior walls. It’s now believed that those walls impeded airflow and trapped contaminates that are otherwise vented out of one-room tent cabins.

Is it really safe to stay in the other Yosemite tent cabins?

The scientists studying the Yosemite outbreak believe that to be true - so much so that they’re sleeping in tent cabins at Curry Village during their investigations, although not the signature cabins.

What should I do if I stayed at a signature tent cabin and start showing symptoms?

Call your doctor immediately and ask for a blood test, which can confirm whether you’ve contracted HPS.

If I stayed in the signature tent cabins, became sick and now feel better, should I contact health authorities?

Yes. Tell your doctor. The information you provide will help health officials learn more about the disease – specifically why one person in an infected cabin became ill while another did not.

Where else in Yosemite has hantavirus been identified this summer?

Officials have so far linked one infection to one of four camps along the High Sierra Loop, a popular backpacking route. That person, who recovered from his infection, told health officials he stayed at the Merced Lake, Sunrise and Vogelsang camps and the Tuolumne Meadows Lodge. Health officials are now investigating those areas.

Are deer mice at Yosemite more likely to have hantavirus than deer mice found elsewhere in California?

No, and actually the opposite is true. The incidence of hantavirus in the deer mice tested at Yosemite is actually lower than the statewide average (14 percent in Yosemite vs. 15 percent statewide). But because mouse population is a dynamic and fast-renewing one, the rate of infection varies somewhat.

Yosemite National Park has set up a public information hotline staffed from 9 a.m. to 5 p.m. daily at (209) 372-0822. All messages left will be returned by a park ranger.

For more information:

Centers for Disease Control and Prevention Hantavirus webpage

National Park Service Hantavirus Camping Information