White-nose syndrome has killed at least 5.7 million bats across the U.S. and Canada since 2006, but it's still not slowing down. Wildlife authorities reported this week that the mysterious fungal disease has now reached Alabama, its southernmost occurrence yet in North America.

"White-nose syndrome had been confirmed in several counties in Tennessee, but had yet to be discovered in Alabama until this year," Alabama state biologist Keith Hudson says in a press release. "This disease is likely one of the most significant disease threats to bat populations in Alabama due to its potential to affect multiple bat species and the devastating nature of the affliction."

A team of scientists made the discovery during a March 1 survey of Russell Cave in Jackson County, where they found "numerous bats displaying symptomatic white patches of fungus on their skin." They took tissue samples and sent them in for testing at the University of Georgia, which confirmed the presence of white-nose syndrome.

WNS first appeared in upstate New York in 2006, and has since spread to 17 states and four Canadian provinces. The U.S. Fish and Wildlife Service reported in January that the disease has now killed 5.7 million to 6.7 million cave-dwelling bats in eastern North America, with mortality rates as high as 100 percent in some caves. Biologists aren't sure exactly how the disease works, but infected bats often wake up from hibernation too early, flying out into the cold at a time when food is scarce.

Little is known about WNS, although scientists did recently discover its cause: a previously unknown type of fungus called Geomyces destructans. The disease is known to be transmitted mainly from bat to bat, although researchers believe it's also inadvertently carried between caves by humans, since the fungal spores can stick to clothing or shoes. A variety of caves have been closed in an attempt to slow the spread of WNS, but it's unclear how effective that strategy has been.

"The National Park Service has been working closely with state and federal agencies and has implemented protection protocols to try and limit the spread of this deadly disease," says John Bundy, superintendent of Russell Cave National Monument. "Although the cave system has been closed for 10 years, access to the park's archeological site remains open."

The rapid and severe loss of bats to WNS isn't just an ecological problem — it's also an economic one. In addition to eating gnats and mosquitoes that annoy people and spread disease, bats also help control the populations of other insect pests that can damage agricultural crops. As the Alabama Department of Conservation and Natural Resources estimates, "Insectivorous bats likely save the U.S. agricultural industry at least $3 billion each year, or approximately $74 per acre for the average farmer."

Fifteen species of bats are native to Alabama, including gray and Indiana bats, which are both endangered. The arrival of WNS is a major setback, but Mike Armstrong of the FWS says the U.S. won't let up in its fight to contain the fungus. "We have worked closely with [state agencies] to prepare for white-nose syndrome," Armstrong says in a statement. "Now that it is confirmed here, we will continue to work with the state and our federal partners in their research and management of the disease."

For more about WNS, see this explainer, as well as the map and related links below:

Also on MNN:

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

White-nose syndrome spreads to Alabama
With about 6 million dead bats already left in its wake, the killer fungus now marks its southernmost extension yet in North America.