Hantavirus in Yosemite may be shape of things to come

10:03 AM, Sep 29, 2012   |    comments
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YOSEMITE NATIONAL PARK - Hantavirus in Yosemite. West Nile virus in 48 states. Even a case of bubonic plague.

"I hear locusts are next," says Cathi Soriano of Seattle, who recently took Yosemite National Park off a road-trip itinerary.

Are we under siege?

Not really, but the medical victories we've experienced over the past 100 years have made Americans forget that such diseases haven't gone away, says David Dausey, director of the Institute for Public Health at Mercyhurst Universityin Erie, Pa. "It's unsettling to realize that we're not entirely safe from these things."

The rise of hantavirus and West Nile virus, neither even recognized in the United States before 1993, is making people check their window screens, stock up on bug spray and rethink travel plans. In Yosemite this summer, hantavirus has killed three people out of nine sickened. Nationally, West Nile virus is the worst it's been since the disease arrived on our shores in 1999: more than 3,545 illnesses and 147 deaths as of Thursday.

Extreme weather patterns have played a big role in the two recent outbreaks, and health officials worry more such events could be on the horizon because of climate change.

Climate cycles very clearly play a part in outbreaks, says Michael Osterholm,director of the Center for Infectious Disease Research and Policyat the University of Minnesota in Minneapolis. The question is at what point any given outbreak is being caused by climate change or simply normal weather cycles. However, it's clear that "eventually (climate change) will affect things, but is it now? We don't know," he says.

At the same time, health officials fret that the public health infrastructure of laboratories and public health workers that tracks and responds to outbreaks is being cut. That could make outbreaks harder to detect and control.

"The federal spigot is not just being cut off, it's being smashed," Osterholm says. "We've got a crash coming. We can see it."

In the hantavirus outbreak at Yosemite, weather and a move to provide more economical lodging for winter sports enthusiasts could be behind the illnesses. Three deaths are worrisome but doctors are particularly taking notice because they came in a tightly focused geographic cluster.

"It's never happened before," says Pierre Rollin, a chief with the Centers for Disease Control and Prevention's Special Pathogens Branch.

On a brilliant fall day, it's impossible to get into the park and not hear about hantavirus.

"They gave me a pamphlet when I came through the main gate, then one when I checked in (at Curry Village), and there was one on my bed when I got to my cabin and one pinned to the wall. And there's one in the bathroom," says Rebecca Costello of Ambleside, England. "Those people up there," she says, pointing at rock climbers clinging to the Half Dome are "in a lot more danger than I am here.""Now's probably the safest time to be here," agrees Nicole Swedlow, 38, who runs a children's charity in San Pancho, Mexico. "They've got people all over it."

Phillipe Brachais, 30, of Antwerp, Belgium, has no worries about staying nearby. "It's only three people dead, and millions come here every year," he says.

His companion, Fabienne Verwerft, 29, says her only concession was to buy some hand sanitizer before they arrived.

There have been some cancellations, but park visitors are still on track to reach the September average of about 17,000 people a day, said Tom Medema, chief of interpretation and education at Yosemite National Park.

But in the background, epidemiologists, wildlife biologists and researchers are catching and testing mice, taking environmental samples and contacting people who stayed in the area -- those who got sick and those who didn't -- to see how their visits differed.

Hantavirus has long been known in the United States. Every year from 11 to 48 people -- mostly in the West and Southwest -- come down with it, and about 33% of them die. But never in clusters, as at Yosemite. That's why the National Park Service has sent letters and e-mails or made phone calls to more than 260,000 overnight guests who stayed in the park since early June to warn them, Medema said. So far, no park workers are known to have come down with the virus, Medema said.

On Wednesday, the park began a pilot survey to draw blood samples from approximately 100 employees to find out if they had been infected with hantavirus in the past. Because most people who get hantavirus don't have symptoms, it's possible others have gotten it before but no one knew. Once the pilot survey is completed the park hopes to open it to all staffers. This "may make an important contribution to our knowledge about this rare virus," Medema said.

The virus is carried by deer mice, which live across the United States. People get it by breathing in aerosolized mice droppings and dried urine -- that is, mouse dust -- so victims have to be in close contact with the mice or their nests. It is not transmitted between humans.

The Yosemite outbreak is still a medical mystery, one that dozens of wildlife and health experts are combing the park to solve. It is known that wet summers give mice ample food, allowing populations to climb. Follow that with a mild winter, as last winter was, and it's a problem.

"It's the adults who survive the winter who transmit the virus," says Danielle Buttke, a veterinary epidemiologist with the U.S. Public Health Service in Fort Collins, Colo., who was in Yosemite investigating the outbreak. If the summer then is especially dry, all those mice are looking for food and homes -- which they found in the tent sites at the park's Curry Village.

The first big U.S. hantavirus outbreak in 1993 "was a very wet summer followed by a mild winter," Buttke says.

In 2009, in the category of possible plain bad luck, the park added insulation to some tents to replace winterized cabins destroyed in a massive rock fall in 2008.Unfortunately, mice love to live in insulation, says Gregory Glass, a hantavirus specialist and professor of infectious disease ecology at Johns Hopkins University in Baltimore.

"It may just be one of those situations where, historically, when they didn't insulate them, it wasn't that attractive for the mice to sit and stay," he said. "But this one little tweak in the design made just that much of the difference for mice."

West Nile has certainly had a bumper year because of the weather. The Culex mosquito that carries the virus prefers breeding in the murky bottoms of drying pools and water sources -- exactly what happens in droughts. And this year drought has scorched the nation at levels surpassed only twice before, according to the National Climatic Data Center.

People such as Osterholm worry that we're gutting our ability to fight such outbreaks when more extreme weather is in our future. With West Nile virus, a mosquito-borne disease, cutbacks have hit local mosquito abatement districts nationwide, from the loss of a few staff members to the closing of North Carolina's entire mosquito Pest Management Section. CDC's Vector Borne Diseases group, which works on West Nile virus, among other diseases, has lost $14 million in funding since 2005, 38% of its budget.

"It's easy to count how many police or firefighters you have," Osterholm says. But no one's counting how many public health people who can respond to a crisis are losing their jobs. "We're going to wake up one morning and say, 'There's a big outbreak somewhere,' and people will ask who's responding, and we'll say, 'We don't know -- we don't really have anyone there.' "

The one episode this summer that didn't appear to be anything other than normal was the case of bubonic plague in 7-year-old Sierra Jane Downing of Pagosa Springs, Colo. Doctors believe she caught it from fleas off a dead squirrel she encountered while picnicking with her family.The bacterium that causes plague, Yersinia pestis,is found in rodents and their fleas in many parts of the world, including the United States. Every year five to 15 people catch it, according to the CDC.

Doctors at Rocky Mountain Hospital for Children in Denver, where she was being treated, quickly realized she had the plague and gave her the appropriate antibiotics. She went home after 2½ weeks in the hospital.

Elizabeth Weise

USA Today

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