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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Sources: Centers for Disease Control and Prevention, California Department of Public Health, the U.S. National Library of Medicine, National Park Service.