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Testing Finds No Hantavirus In Yosemite Valley, Some At Tuolumne Meadows Lodge Area

A testing program put in place after three Yosemite National Park visitors died in 2012 from a rodent-borne disease detected no hantavirus in the park’s iconic valley last year, though some was detected in the area surrounding Tuolumne Meadows Lodge, according to the California Department of Public Health.

“In 2014, three rodent trapping events were conducted. Two were conducted at select locations in Yosemite Valley. A third trapping event was conducted in the Tuolumne Meadows Lodge area,” Matt Conens, a spokesman for the department, told the Traveler. “A total of 66 mice were trapped in Yosemite Valley in 2014 and tested for antibodies to Sin Nombre virus. None tested positive.

“In the Tuolumne Meadows Lodge area, eight of 65 (12.3 percent) mice tested positive for SNV antibodies in 2014. For comparison, the prevalence of SNV antibodies in deer mice sampled from 42 counties in California from 2004-2013 was 11.6 percent.”

Traveler sought the test results after a reader mentioned a mouse problem in their room at Yosemite Lodge at the Falls recently and wondered if any testing for hantavirus was being done.

“The mouse was there from the first night. The last morning there were droppings on the table where a lot of our stuff was. We informed the desk when we checked out,” they wrote.

During the summer of 2012, ten Yosemite visitors who had stayed in tent cabins in Curry Village in Yosemite Valley were infected by the rodent-carried disease, which produces flu-like symptoms and can lead to fatal respiratory complications, and three died from it. Nationally, the death rate from hantavirus is 38 percent, according to the Centers for Disease Control and Prevention.

At the time, park officials and those with Delaware North at Yosemite, the lodging concessionaire, reached out to more than 200,000 visitors who stayed in the park from early June through late August of 2012, including some who came from overseas, to alert them to the outbreak and to urge them to seek medical attention if they come down with any of the flu-like symptoms the disease spawns.

The outbreak led to the discovery of deer mice nesting within the double-walled Signature Tent Cabins. It would, in theory, be possible for urine-contaminated dust from those nests to migrate into the cabin’s interior and transmit hantavirus to those staying in the cabins, an epidemiologist for the National Park Service who investigated the outbreak told the Traveler at the time.

Since the outbreak, Delaware North staff “continues to clean and maintain its facilities consistent with National Park Service policies and practices, which are designed to prevent exposure to hantavirus. Part of the policy includes responding to guest notifications regarding rodent activity,” Lisa Cesaro, a company spokeswoman, said last week.

In a report published by the Centers for Disease Control and Prevent after the 2012 outbreak, researchers wrote that, “(S)taying overnight in a Signature tent cabin (9 case-patients) was significantly associated with becoming infected with hantavirus. Rodent nests and tunnels were observed in the foam insulation of the cabin walls. Rodent trapping in the implicated area resulted in high trap success rate (51%), and antibodies reactive to Sin Nombre virus were detected in 10 (14%) of 73 captured deer mice. All (91) Signature tent cabins were closed and subsequently dismantled. Continuous public awareness and rodent control and exclusion are key measures in minimizing the risk for hantavirus infection in areas inhabited by deer mice.”

The researchers considered the outbreak “unusual because it was associated with exposure to rodents in a specific type of housing. Yosemite’¬ôs Signature tent cabins were unique to the Boystown area in Curry Village and were not located elsewhere in Yosemite or in the NPS system. They were constructed in 2009 with dry wall and foam insulation to provide lodging for guests during winter. The presence of active deer mouse infestations within the insulated spaces of the cabins likely increased the risk for SNV exposure for persons staying overnight in these cabins.