Yosemite Workers Could Yield Clues Into 2012 Deadly Hantavirus Outbreak
October 17, 2012

Yosemite Workers Could Yield Clues Into 2012 Deadly Hantavirus Outbreak

Lawrence LeBlond for redOrbit.com - Your Universe Online

As many as 2,500 Yosemite National Park employees will be interviewed and have their blood drawn as health experts continue to search for clues as to what caused this summer´s deadly hantavirus outbreak.

The Yosemite hantavirus outbreak, the biggest to strike the US in nearly two decades, has taken the lives of three people and has infected at least six others who have visited the park since early this summer. The initial three illnesses and a death, reported in late August, prompted park officials to look more closely into the issue, investigating the park´s camps for possible signs.

After a second death was reported and it was clear an outbreak was on their hands, park officials closed down the park´s popular Curry Village where the infection was believed to have originated. Work crews cleaned all of the village´s signature cabins and worked to secure them from further breach from deer mice, a known vector of hantavirus. Park officials also put out a warning to nearly 3,000 people who had visited the park between June and August, alerting them of a possible risk of infection.

When the third death was reported, state health workers and experts from the CDC got involved and raised the alert to include 10,000 past visitors to the park. Experts also looked more closely at the park´s deer mice population. Studies in recent years have shown a fairly stable population. But this year, researchers have found, based on trap catches, the deer mouse population has climbed significantly. Shortly thereafter, a worldwide alert was issued, extending to nearly a quarter-million people who may have visited the park since early June.

While there has yet to be any more deaths reported from the Yosemite outbreak, health experts are not taking any chances. To better understand what they are dealing with, park epidemiologists and state health workers are taking blood samples from some 2,500 park workers and having them answer questionnaires. They are hoping to get a number on how many park workers may have been exposed to the virus and why some people get sick and others don´t.

The voluntary screening, taking place over the past few days, is the most recent effort to shed light on the disease.

“This is a highly unusual situation,” Barbara Materna, chief of the California Department of Public Health's occupational health branch, told Reuters´ Ronnie Cohen. “It is the largest outbreak of hantavirus that we've seen. We're looking at it as an opportunity to learn more about this condition, how exposure happens and how to prevent it.”

The number one question health experts have is why the virus has infected park visitors while park employees have seemingly been spared. Other questions will cover living conditions, contact with rodents and whether any hantavirus training was offered.

Materna said her team had arrived at the park on Monday to begin the survey and by the end of the day only 300 of the some 2,500 workers had signed up. She said the survey is part of a broader study, which includes the first whole-genome sequencing for the hantavirus strain that struck Yosemite this past summer.

Danielle Buttke, a veterinary epidemiologist with the National Park Service, said the infection rate for trapped mice in and around Yosemite Valley is about 14 percent, a California-wide average. However, she explained, deer mice that live in areas with natural predators usually do not carry the virus.

One of the positives of the park´s aggressive deer mouse trapping campaign is to mimic results shown by natural predation in the hopes that the virus strangles itself out. “We need to do further research to see if we can influence that,” Buttke told the Associated Press.

Health experts believe many cases could have gone undetected as many people may have had only mild symptoms and passed it off as typical influenza and just let it run its course. It is also likely many more may have never even developed symptoms.

Humans have never been known to transmit hantavirus, which is picked up through breathing contaminated dust particles. However, getting a better grip on the virus now will be a significant step in case the virus ever mutates into a transmissible strain.