In a cave in New Brunswick, Canada, the disease hit hard. "It hit our biggest hibernacula first,” recalls Karen Vanderwolf , a Phd student who studies fungal diseases at the University of Wisconsin at Madison. “There were thousands of dead bats littering the cave floor ... a carpet of dead bats." Something she wasn’t prepared for, she adds, was “the smell ... I'll never forget it." That was in 2011. Two years later, it had spread to every known cave in the region.

The New Brunswick bats had been decimated by white nose syndrome—a fungus-caused disease that kills bats by interrupting their hibernation, causing them to use up fat reserves before winter is over. The animals usually starve to death before spring. In winter 2006 , "Patient Zero" for the outbreak was found in Howes Cave near Albany, New York. By 2010, it had spread to Fort Drum, a U.S. Army military installation upstate that is home to multiple bat colonies spanning eight species.

One of those colonies today includes nearly 200 little brown bat mothers and babies. But 15 years ago, the colony contained over 1,000 adults, and hundreds more babies. "It was pretty depressing," says Chris Dobony , an army biologist at Fort Drum who has watched the disease ravage the colony over the past decade. "We lost close to 90 percent of the colony."

By the numbers, the situation sounds pretty hopeless. White-nose has killed millions of bats and wiped out entire colonies across North America, and shows no signs of abating. Cases have been found up and down the East Coast, as far west as Texas and Oklahoma, as far south as Georgia, and north into Canada, according to WhiteNoseSyndrome.org , a website operated by the U.S. Fish and Wildlife Service. (Isolated cases have also been found in Washington State.)

But new research is pointing toward cautious optimism: Scientists studying the fungal killer are beginning to shed light (literally) on previously unknown weaknesses, and even identify other fungi they could enlist in the struggle. And the bats may have a few surprises of their own.

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Daniel Lindner , a mycologist with the U.S. Forest Service, is an expert in identifying fungi using DNA in difficult or complex environments. Around 2008, after authorities began to suspect that p. destructans was the cause of white-nose syndrome, Lindner was asked to help design a better test to test for the presence of the fungus. It’s part of a group of fungi that are "particularly understudied," he says; until 2013, it was actually thought to be part of a different genus.

Linder quickly learned that P. destructans and its ilk are not just cold-loving, but require cold to grow. Most labs don't bother studying such finicky organisms until, like p. destructans , they start "doing something that humans take notice of," as he puts it.

What they had on their hands was a cold-loving fungus that was killing bats, growing in environments alongside anywhere from three dozen to three hundred of its close relatives that weren’t killing bats. The team decided to take a close link at the deadly fungus’ DNA, which was “a very difficult genome to work with," Lindner notes. "It has a lot of repetitive DNA in it. It becomes a difficult problem to process and sort through and find this needle in the haystack."

Thanks to Lindner's colleague John Palmer, the team noted two things. First, the genome was missing something crucial: more than half of the enzymes the fungus would need if it lived in soil. Instead, it seemed the fungus only thrived on bat bodies themselves. "Everything about the genome of this fungus, to me, suggests a true bat pathogen—something exquisitely adapted to living on bats," Lindner says.

The second weakness, though, may prove to be the most useful. Unlike its close relatives, P. destructans was also missing the "DNA machinery" to repair damage from ultraviolet light. In other words, simple sunlight was deadly to this fungus. "It's not just that the machinery for repairing UV light damage was damaged or broken, it seemed to be entirely missing," Lindner says.

The researchers believe that p. destructans has been diverging from its relatives for 20 million years, and is now entirely dependent on dark cave environments to live. The fungus has “truly become a creature of the dark,” says Lidner. "I have trouble not thinking of vampire movies—when you pull back the shades and it goes up in a cloud of smoke."

This night-loving nature makes bats the perfect vector: they live in caves, move from place to place, and only travel at night. But this fact also brings slight hope to bat lovers. Theoretically, one could set up a tunnel at a cave entrance that zaps the bats with a low dose of light as they fly out to hunt insects. This would be complicated and difficult, and is entirely theoretical at this point, but Lindner and colleagues at Bucknell University are running the first tests on infected bats this summer.

If it works, the UV tunnel could "find and potentially treat a significant proportion of the bats without having to go into the [cave]," Lindner says.

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Other scientists are working a different approach: fighting fungi with fungi. A recent study in the Journal of Fungi reports that “mushroom alcohol” (a compound produced by some shrooms when they break down linoleic acid) inhibits the growth of p. destructans . (Humans produce a small amount of "mushroom alcohol" in their breath—and it attracts mosquitoes. Who knew!) The same study also found that leaf aldehyde, a antimicrobial compound that plants produce, is even more effective.

"The interesting thing about some of these volatile organic compounds is they may not even kill the fungus," says Lindner. "This seems like splitting hairs, but [the VOCs] are fungistatic, versus fungicidal." In other words, they stop the mold's growth without killing it, which might leave the rest of the bat's microbiome intact. "I think these VOCs are exciting as a treatment option," he says.

Again it comes down to delivery. Given that caves are vast, complicated and full of tiny crevices that bats can reach but humans can't, filling a cave with mushroom alcohol or another VOC at the appropriate concentrations will be challenging. Still, early trials show promise. Chris Cornelison, a research assistant professor at Kennesaw State University, filled Black Diamond Tunnel, an abandoned railway tunnel in northern Georgia, with an antifungal agent in 2017 using a “bat fogger.” In April 2018, a bat survey turned up 178 animals, 26 more than the previous year . More research is certainly needed, but for now, it's being interpreted as a glimmer of hope.

Until then, scientists gain hope from a new development: some infected bat colonies are managing to bounce back. If scientists could find out what it is the bats are doing differently, they might be able to help these colonies help themselves.

Back at Fort Drum, for instance, the little brown bat maternal colony seemed headed for extinction. Until...it wasn't.

In a recent study, Dobony and colleagues describe how the bat maternity colony may not be exactly thriving in the same numbers as pre-White Nose, but it is persisting. From a low of about 90 adult bats in 2010, the colony has recovered to almost 200, Dobony says. And even the mother bats that are infected with white-nose are reproducing at their normal rate of one to two pups per year.

Before Dobony and his team started monitoring this colony, nobody knew whether the surviving remnants of bat colonies would be able to do more than just hang in there—if they could actually "be an effective portion of the population," he said.

For now, we don’t know why. Could it be behavioral? Could it be genetic—that thanks to natural selection, the bats that had a natural resistance to the fungus managed to survive? "These guys, whatever they're doing, they're coming back and being normal once they get here." T

Similar stories are starting to appear elsewhere in the Northeast; Dobony says he's heard of colonies stabilizing in New Hampshire and Vermont. But not every colony is stabilizing. Scientists are now studying the ones that are rebounding to glean lessons, since their small numbers mean their survival is still precarious. (A heavy storm that kills 50 bats is sad for a colony of 1000, for instance, but a tragedy for a colony of 200.)

"We as humans like to fix things," Dobony says. "Certainly if there's something we could manipulate that would help these populations out, it'd be a possibility ... but these guys have survived and started rebounding without our influence.” In other words, at least for some colonies, the answer might just be leaving them alone.

Lindner, the mycologist, says his optimism fluctuates day by day. "It's hard when there's news each day about new states [with infected populations] and new species of bats where the fungus has been detected. I am more hopeful," he says, about protecting the remnant populations. The best-case scenario would be for humans to help the bats hang on long enough "to help natural selection take over at some point,” he says. “That's the goal.”