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Hantavirus Infects At Least Nine Visitors to Yosemite this Summer

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October 5, 2012

The U.S. National Park Service has reported that at least nine people who stayed in Yosemite National Park, California at least one night since June of this year have been infected with a rodent virus called hantavirus. People contract hantavirus by coming in contact with the dust or airborne particles of infected rodent droppings, saliva or urine; however, many people become ill without having seen rodents or their droppings, according to the Centers for Disease Control and Prevention (CDC).

There are several different strains of hantavirus that cause a range of disease symptoms. Anyone who is exposed to hantavirus from infected rodents can develop Hantavirus Pulmonary Syndrome (HPS), a very serious and sometimes fatal disease, says the CDC. Avoiding contact with rodent droppings, urine and saliva is the only known prevention for the hantavirus. There has been no documented evidence of person-to-person transmission of the strains of hantavirus isolated in North America, Europe and Asia.

Of the nine Yosemite campers who were diagnosed with a confirmed case of hantavirus, three have died and the other six have recovered. The National Park Service has contacted about 30,000 people who stayed in the same lodgings that the infected park visitors stayed in and is advising them to contact a health care professional if they develop concerning symptoms. A public service message aimed at reaching more than 230,000 past Yosemite visitors was sent by the National Park Service on September 12, intending to inform the public about the disease and address questions and concerns.

According to the CDC, initial symptoms of HPS can begin one to five weeks after a person is exposed to the virus. Early symptoms can include fatigue, fever, chills, and muscle aches, and about half of patients have headaches, nausea, vomiting, dizziness, and abdominal pain. HPS progresses quickly, and about four to ten days after the first symptoms appear, more severe symptoms including coughing, shortness of breath, and extreme difficulty in breathing can occur.

Because the early symptoms of HPS are similar to other conditions such as the flu, it can be difficult to identify and begin supportive care for the patient, which is why at least some of the deaths occur. The National Park Service is working with state public health agencies to help alert people who spent at least one night at Yosemite this summer to contact their doctor if they have any of the symptoms described, to let the doctor know they may have been exposed to hantavirus, and to get tested.

To determine whether a person is infected with hantavirus, a laboratory test that can detect antibodies to the virus is performed on a blood sample. A positive result is an indication that someone is likely infected. There is no specific antiviral treatment for hantavirus, but patients who are admitted into intensive care and given oxygen to help them through the most severe period of respiratory distress tend to do better, and the earlier they are treated the better.

In the U.S., the rodents most likely to carry hantavirus are deer mice, which can harbor a form of hantavirus called Sin Nombre. Cotton rats and rice rats in the Southeast and white-footed mice in the Northeast can also harbor and spread hantavirus. The virus is more likely to occur in rural areas where rodents nest in forests, farms and fields. At Yosemite, the virus was likely spread by deer mice in the campgrounds, according to the CDC.

Despite the recent outbreak, HPS is a relatively rare, though life-threatening infection. According to the CDC, through December 31, 2011, a total of 587 cases of Hantavirus Pulmonary Syndrome have been reported in the United States, and 36% of all reported cases have resulted in death.

The CDC maintains a Hantavirus Hotline (877-232-3322 and 404-639-1510) and information about HPS on its Hantavirus web page.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used. To access online sources, copy and paste the URL into your browser.

(September 26, 2012) National Park Service. Yosemite National Park, Hantavirus in Yosemite. Available online at through Accessed September 27, 2012.

(September 26, 2012) National Park Service. Yosemite National Park, Hantavirus Frequently Asked Questions. Available online at through Accessed September 27, 2012.

(September 17, 2012) Centers for Disease Control and Prevention. Outbreak of Hantavirus at Yosemite National Park. Available online at through Accessed September 27, 2012.

(August 29, 2012) Centers for Disease Control and Prevention. Hantavirus, Reported Cases of HPS. Available online at through Accessed September 27, 2012.

(August 29, 2012) Centers for Disease Control and Prevention. Hantavirus, Diagnostics. Available online at through Accessed September 27, 2012.

(August 29, 2012) Centers for Disease Control and Prevention. Diagnosing and Treating Hantavirus Pulmonary Syndrome. Available online at through Accessed September 27, 2012.