Investigation of Yosemite Hantavirus Outbreak Leads to Worker Screening

As part of the continuing investigation into the recent hantavirus outbreak at Yosemite National Park, public health officials are now screening more than 2,500 employees who work at the park. 

The voluntary screening will examine blood samples from park employees in an effort to find antibodies of the virus and identify potential indicators of exposure to hantavirus in Yosemite.

At least nine visitors who stayed at Yosemite National Park in recent months have been diagnosed with hantavirus, including at least three deaths.

The infections can incubate for weeks before symptoms appear, which may include problems similar to what is seen with the flu, such as fever, headaches, muscle aches, stomach problems, dizziness and chills. However, hantavirus has a death rate of about 38 percent, since the condition often goes undiagnosed and without treatment.

The Yosemite hantavirus outbreak has been linked to deer mice that have infested certain campgrounds, including the Signature tent cabins of Curry Village and High Sierra Camps.

The screening is part of a larger scientific research effort including genome-sequencing for the hantavirus strain that afflicted Yosemite this past summer.

Yosemite Park Searches for Answers

Dr. Charles Chiu, from the University of California-San Francisco, and his team of researchers are hoping to find answers on why park employees were able to avoid infection of the virus while visitors were not.

Employees will provide blood samples and answer a questionnaire about their living conditions, location, contact with mice, job duties and any hantavirus training. Researchers desperately search for clues linking the infection of hantavirus to only some people and ways to prevent the virus.

Officials speculate extensive hantavirus training among employees may have contributed to their ability to avoid infection of the virus, while visitors could not.

Hantavirus Warnings Provided to More Than 230,000 Yosemite Visitors

The park initially contacted 1,700 visitors to the Curry Village area during the summer months; but later expanded their warnings to more than 230,000 visitors of the overall park itself in order to allay concerns of visitors from this summer.

The outbreak this summer at Yosemite marks the largest cluster of cases of the hantavirus since the disease was identified in 1993.

A 2010 report from the California Department of Health suggests that Yosemite officials may have known about the potential risk of a hantavirus outbreak two years prior to this summer’s event, raising questions about whether sufficient steps were taken to protect visitors or warn about the risk of hantavirus at Yosemite National Park.

The report warned Yosemite officials against a potential risk of hantavirus citing a need for increased rodent inspection efforts and more stringent measures to keep the mice away from the sleeping campers. The “signature” tent cabins have a double-walled design that offers an ideal spot for rodents to nest in.

Hantavirus is a rodent-borne lung disease contracted through contact with urine or droppings of infected deer mice. According to the National Park Service, as many as 20 percent of Yosemite’s deer mice, a common carrier of the virus, are infected.

Photo Courtesy of MiguelVieira via Flickr/CC 2.0