A fatal fungus, revealed

The death toll continues to mount in Eastern caves: Since the winter of 2007, when bat behavior turned erratic in upstate New York and state wildlife officials discovered thousands of bats dead in a cave near Albany, their noses smudged with a curious white substance, a million more have succumbed to a disease called white nose syndrome. 

The disease has been, in a word, devastating. It's wiped out upwards of 90 percent of bats in infected caves. As HCN contributing editor Michelle Nijhuis reported for Smithsonian recently:

By the end of 2008, wildlife-disease researchers had identified the (white) fuzz as a fungus new to North America. Today the fungus has spread to 19 states and 4 Canadian provinces, and infected nine bat species, including the endangered Indiana and gray bats. A 2010 study in the journal Science predicted that the little brown bat -- once one of the most common bat species in North America -- may go extinct in the eastern United State within 16 years.

Scientists have suspected for some time that the fungus to blame was Geomyces destructans. But as Nature News reports, they couldn't be sure: "The culpability of G. destructans for this sudden outbreak was thrown into question when the fungus was found on healthy bats in Europe, where it is not associated with the grim mortality levels seen in North America. Some proposed that the fungus was not the primary cause of the catastrophic die offs, and that another factor -- such as an undetected virus -- must be to blame."

Now, they've got their proof. A study published last week in Nature confirms that G. destructans is the cause of the disease. It's an important step for efforts to protect bats, since it's difficult to fight an enemy you only sort of know. The research will "help us focus our actions or management efforts in the future," Jonathan Sleeman, director of the National Wildlife Health Center, told Science News. As for why the fungus hasn't crippled bats across the pond, mycologist Vishnu Chaturvedi told PBS' blog The Rundown, "It could be that European bats have evolved over a longer period of time and are immune or have a different way of coping with the fungus during hibernation. Or the fungus in the U.S. has subtle variations that we have not even started looking at."

The disease still hasn't shown up in the West. But as we reported last summer, some scientists think it inevitably will. It is creeping closer: The fungus has been discovered as far West as Oklahoma, though it supposedly hasn't killed bats there. If it does arrive in our region, the impacts could be more muted than out East. "Some scientists believe that Western caves are generally too warm and dry to support the fungus, ... and that the region's bat hibernation colonies are too small and spread-out for white nose syndrome to take root," Madeline Bodin wrote for HCN.

For now, says Katie Miller, a Nevada Department of Wildlife biologist and co-chair of the Western Bat Working Group's white nose committee, "We're in prevention mode." She doesn't expect the Nature study to change the work that's already underway. "The study says the primary mode of (white nose) transmission is bat to bat. There's no way for us to manage that. So our goal in the West is to manage people." It is believed that people can spread the fungus by tracking it into caves on their clothing and gear. So Western states are doing what they can to make sure cavers and scientists sanitize their clothing before entering caves. And white nose has given agencies a new reason to try to keep people out of abandoned mines, which can also host hibernating bats.

Miller says a few Western states recently secured a federal grant to collect basic information about the region's bat populations. "Bats are really cryptic and mobile. We don't know anything at all about population levels in the West," she says. "If we can have that baseline data, if (white nose) does make it out here, it'll let us know how badly we're getting hit. Back East, they don't know that. ... I'm pretty sure Vermont would've loved baseline data."

Cally Carswell is HCN's assistant editor.

Photo: A little brown bat with white nose syndrome, courtesy of U.S. Fish and Wildlife Service.