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Yosemite makeover seeks to keep hantavirus at bay

Last year, three visitors died and six became ill when they were infected by the rodent-borne illness. The park has spent millions working to mouse-proof lodging.

May 25, 2013|By Eryn Brown, Los Angeles Times
  • Carpenter Steve Lovejoy installs doors on the new cabins at Yosemite National Park's Camp Curry in March. Last year a hantavirus outbreak sickened and killed several visitors.
Carpenter Steve Lovejoy installs doors on the new cabins at Yosemite National… (Mark Boster, Los Angeles…)

YOSEMITE NATIONAL PARK — Sisters Lauren Scott and Patrice Fambrini stood near the check-in desk of Curry Village, a quaint collection of tents and cabins in Yosemite National Park, and considered the merits of their lodgings.

Last year, three people died and six more became ill after staying at the campground — infected by a rare, mysterious and usually dangerous rodent-borne illness known as hantavirus.

"The way these were constructed created a habitat for the mice to be there," Fambrini said nervously.

Scott, a longtime fan of the camping area, was unfazed: "You're in the woods!"

It may not have been apparent to the sisters, but Curry Village has become ground zero of a multimillion-dollar effort to make Yosemite safe — or as safe as any rural place can be — from an illness carried by creatures who can burrow into a hole the width of a pencil. Changes to the park's far-flung facilities will get tested this summer, as an expected 1.8 million visitors fan out across its 1,200 square miles and share turf with all sorts of wild beasts.

The park visitors who contracted hantavirus had inhaled large quantities of dust containing urine, saliva and fecal matter from infected deer mice. To try to keep that from happening again, workers have been plugging crannies in buildings, hanging screens on staff and guest lodgings, and reinforcing "bear boxes," all to keep the little critters from nesting anywhere near people.

It's an undertaking that's considerably more difficult than guarding against ferocious predators, said Mark Gallagher, environmental manager at Yosemite for Delaware North Cos., which operates Curry Village and other lodging facilities in the park.

"Keeping a bear out is easy — your enclosure just has to be strong," Gallagher said. "With a mouse, you really have to pay attention to detail."

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Signs that something was awry in Yosemite began with the case of a visitor who had stayed in Curry Village's so-called signature cabins — canvas tents fortified with drywall — in June. The patient suffered fatigue and fever, and had trouble breathing. Tests revealed hantavirus.

The Sin Nombre strain of hantavirus was identified in the Four Corners region of the Southwest in 1993, and it's typical for a handful of people to fall ill each year. But those cases are usually isolated. So when a second patient who had stayed at Curry Village in June tested positive for the virus, public health investigators began to worry about an outbreak.

In August, the first death was reported.

Investigators from the California Department of Public Health, the National Park Service and the U.S. Centers for Disease Control started pouring into Yosemite. Park operators fielded hundreds of worried calls each day from recent visitors who now had a case of the chills, or a child with a cough. Staff shut down the signature cabins and began contacting the 250,000 people who had stayed overnight in the park that summer.

State health officials drew blood from 569 Yosemite employees to see if any of them had been exposed. Fewer than 1% percent showed evidence that they had.

Across the country in Atlanta, CDC biologists retreated into high-security laboratories to test blood from the sick and tissue from the dead.

Hantavirus is deadly because it provokes a very strong response from the body's immune system, said Dr. Barbara Knust, an investigator in the CDC's viral special pathogens branch who was involved in the Yosemite response.

When a person is infected, white blood cells release chemicals that work to kill the virus. But organs can suffer collateral damage. In the lungs, Knust said, the chemicals cause the cells that line blood vessels to leak fluid into air spaces, making it hard to breathe. They also interfere with the heart's ability to pump blood and maintain pressure in the circulatory system.

Ultimately, 10 hantavirus cases were confirmed: nine in people who had lodged in the signature cabins and one in a man who had stayed at the park's High Sierra Camps, about 15 miles away.

To gauge the extent of the deer mouse infestation, experts from the state health department drew blood samples from more than 100 wild mice. In Curry Village, 14% tested positive for the virus. That was in line with historical averages in the state.

"The problem was something else," said Tom Medema, chief of interpretation at Yosemite.

One potential culprit was the design of the signature cabins. When state health investigators peered between their canvas tent exteriors and drywall interiors, they found droppings and shredded insulation.

Mice — and possibly, hantavirus — had been making themselves at home.

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