Fungus that causes deadly bat disease confirmed in Yakima County cave

May 24—The fungus that causes a deadly bat disease has been confirmed in another spot in Washington, and wildlife officials are urging people to take care in ensuring they aren't helping it spread.

Test results from bat samples taken in Boulder Cave in Yakima County confirmed the presence of the fungus that causes white-nose syndrome.

The disease was first discovered in eastern North America in 2006, where it has killed millions of bats, and it has since spread west.

Washington's first case was confirmed in King County in 2016, and the fungus that causes the disease has since been found in 11 counties on both sides of the Cascades.

Abby Tobin, a Washington Department of Fish and Wildlife bat biologist, said the disease appears to be moving slower in Washington than it has in other states, but that it is still spreading.

"This is just showing that it's continuing to spread at a slower rate than expected," Tobin said.

It also shows that the fungus is present in places that people visit. Boulder Cave is a popular destination on the Okanogan-Wenatchee National Forest, where hikers who reserve a spot online can walk a 1.5-mile trail into the cave. The cave was scheduled to open this week.

Where the fungus is present, it's possible for the spores to get stuck on shoes or clothes, meaning people can inadvertently take it with them when they leave. In a news release, the Forest Service and WDFW urged people to decontaminate their gear after visiting an area where the fungus may be present. Decontamination instructions are available on whitenosesyndrome.org.

The fungus that causes the disease infects bats during hibernation. It thrives in dark, dank places — the same places bats settle in for their wintertime nap.

"Where they like to hibernate is right where the fungus likes to grow," Tobin said. "It's a perfect storm."

It sometimes shows up as a white fuzz on a bat's nose. It infects the skin and can disrupt cell functions, damage wings and interrupt hibernation, causing the animals to burn fat reserves meant to carry them through the winter, which can lead to starvation.

The disease is often fatal, and it can have devastating impacts on bat colonies. In some places, the disease has killed 90% or more of the bats in a given colony.

Tobin said Washington has seen two major mortality events resulting in the deaths of 30 or more bats since the disease was first found here. The first was in 2020 in King County, and the second was this past winter in Benton County.

It can also impact a colony over the long term. Tobin said that colonies they've been monitoring in King County have declined dramatically — in one case, one that had roughly 1,000 bats for years has dropped to about 20 bats over the past several years.

Bats spread the fungus mostly through direct contact. In the East, where bats gather in large numbers each year, it spread much faster than it has in Washington. Here, bats hibernate in smaller groups, which Tobin said likely limits the spread of the disease to some extent.

Still, they've seen it move across both sides of the Cascades, and they've seen it creep eastward toward Spokane County. Benton County is the farthest east that the disease has been confirmed, but the fungus also been confirmed in Montana, Idaho and southeastern British Columbia.

"It's a matter of time," Tobin said.

Washington is home to 15 species of bats, and not all of them are susceptible to the disease. Those that hibernate face the greatest threat, with the fungus having plenty of time to latch on and infect the skin. Some bats don't hibernate, which puts them in a better position to ward off infection.

WDFW and the Forest Service have been monitoring the bats that live in Boulder Cave for years. A test sample from a bat last year returned inconclusive results, but a swab this January from a silver-haired bat confirmed the presence of the fungus.

Tobin said the species can be active year-round, and that the bat didn't show any signs of the disease. But the presence of the fungus still means the bat could spread it elsewhere.

Tobin said she and her team have worked with federal agencies and Canadian officials on possible treatments for the disease. A vaccine is being tested, as is a probiotic. Both are pastes that can be applied on the surface of a cave, where the bats could naturally come into contact with it.

Officials are still trying to determine how effective those treatments could be, but Tobin said they're showing promise.

"It's not getting rid of it, but it's helping to slow the disease enough that the bats don't get a severe infection," she said.