As North American bats face an existential crisis, a new study offers hope for a ravaging disease

When unsuspecting bats are infected with white-nose syndrome, they endure a slow and painful death. The fuzzy white fungus officially known as Pseudogymnoascus destructans covers their wings, tails and muzzles in a thick coat. When bats like the little brown bat (Myotis lucifugus) are afflicted with white-nose syndrome, they take too long to rise from torpor (prolonged hibernation) and struggle to stay nourished as the fungus consumes their bodies' tiny fat deposits. Millions of bats throughout North America have died from white-nose syndrome since it was discovered in 2018, with both professional and amateur chiropterologists despairing for an effective medical treatment. In less than a decade, P. destructans has slaughtered more than 90% of northern long-eared (Myotis septentrionalis), tricolored (Perimyotis subflavus) and little brown bat populations.

Now a recent study in the journal Science offers a glimmer of hope to bat-fans everywhere: Despite the destructiveness implied by its name, P. destrucatans is actually less destructive than previously believed. The mechanisms through which it ravages bats, once mysterious, are now comprehensible.

The fungus infects bats through the epithelial cells of their skin without significantly damaging the cells themselves, the study finds. In addition to making the fungus easier to fight, this discovery helps explain some of the symptoms that it causes in infected bats. By not destroying the skin cells after infecting them, the bats only experience a limited immune response to the deadly pathogen. While their immune systems keep the fungus at bay when the bat is active, the fungus gains the upper hand once the bats enter their state of torpor. Their body temperatures drop, and the fungus finds many ways of adapting and completely infecting the bats' skin cells.

"We created a cell line from an endangered bat species (little brown bat) to create a model for the disease in animals that are not available to be studied," study co-author Dr. Bruce Klein — a professor of Pediatrics, Medicine, and Medical Microbiology & Immunology at the University of Wisconsin, Madison — told Salon. "We created a model of hibernation, which is so critical to understanding of the pathogenesis of the infection."

Prior to their study, the mechanisms behind the fungus' behavior were enigmatic. That is no longer the case, as the study explains its progression at a detailed molecular level.

"We answered these questions by identifying . . . the cells that the fungus invades" and "the receptor that enables entry by the fungus," Klein said, adding that they also studied "the means by which the fungus spreads from cell to cell without killing the cells and thus alerting the bat immune system" and "how the fungus survives inside the harsh interior of the cells."

Dr. Tina Cheng, the director of white-nose syndrome research at Bat Conservation International, was not involved in the study and has studied the deadly disease up-close, albeit not as a microbiologist. She expressed optimism about its implications, assuming its research can be replicated.

"Their findings are incredibly interesting and give unique insight into the 'sneaky' life of [P. destrucatans] and how it avoids host response to proliferate," Cheng said. "The findings of this paper suggest [P. destrucatans] exploits the hibernation patterns of its host and this co-evolution between host and pathogen is consistent with other studies, including a study that found extreme sensitivity by [P. destrucatans] to [ultraviolet] light suggesting specialization on bats and cave environments and a study surmising a plant pathogen origin of [P. destrucatans] that co-evolved with the evolution of hibernation in bats as the planet was cooling millions of years ago."

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Cheng is not the only bat champion enthusiastic about the new research. Dr. Joe Samuel Johnson of the University of Cincinnati also told Salon that from the perspective of his speciality (as an ecologist), he finds the study to be "an exciting piece of work."

"The authors’ inquiry into what is happening with the fungal pathogen both while bats are in torpor and during brief arousals was insightful," Johnson said. "In explaining why [white-nose syndrome] kills bats to students and the public, I often discuss capability of P. destructans to grow at cold temperatures. But the pathogen’s ability to remain infectious during torpid and active states is an important addition to this story. Perhaps more importantly, the authors’ insights into how fungal conidia avoid being killed by bats’ immune cells is likely to be taken up in future studies seeking to understand this deadly wildlife disease."

Johnson also has advice for the general public, or at least that section of it which cares about bats: Protect them when you find them. After all, the bats are literally coming to humans (or at least their structures) for help.

"Most of the species that are vulnerable to this disease migrate away from those habitats in spring to give birth in trees or in human structures such as barns or attics," Johnson said. "Many people have such maternity roosts on their property. And it is here that populations grow each year and provide the possibility of recovery from [white-nose syndrome]. Protecting these maternity roosts, or promoting them where they do not yet exist, is an important part of conservation."

Dr. Susan Loeb, a research ecologist & project leader at the United States Department of Agriculture's Forest Service, said that there are many other things the public can do to protect bats

"Minimizing disturbance to bats when they are hibernating or raising young is critical," Loeb said. "This is particularly important for bats that suffer from white-nose syndrome. If people go into hibernacula or potential hibernacula, they should try to follow decontamination procedures that have been published by the U.S. Fish and Wildlife Service and Canadian Wildlife Health Cooperative." When bats enter mature trees and large snags (dead trees), those organisms should be protected. "These structures provide summer roosts for many species of bats as well as substrate for the insects that the bats eat. Working to maintain forest corridors and clean water will also help bats on a larger scale. Providing alternate roost sites such as bat boxes can help when bats need to be excluded from human structures, but caution should be used to make sure that these artificial roosts are used correctly."

The experts are pressing these warnings on the public because North American bats are facing an existential crisis. Loeb did not mince words; she has seen the devastation firsthand.

"I along with students and colleagues have been monitoring a winter hibernating colony of tricolored bats in an abandoned tunnel in upstate South Carolina since the winter of 2013-14," Loeb said. "Each year we watched the decline of the colony from 321 bats prior to white-nose syndrome down to 31 bats just three years after white-nose syndrome entered the population." The bats have slowly recovered each year, and as of 2024 the population is 123. "Unfortunately, not all hibernating colonies in the area have done as well. For example, a smaller tunnel less than a mile away declined from over 400 bats down to 8 and still has less than 20 bats in it."

Cheng is observing the mass deaths in the Appalachian mountains of Virginia and West Virginia.

"I have also seen the magnitude of these declines by assessing hundreds of sites where [white-nose syndrome] has caused massive declines," Cheng said. "The magnitude of impact of this disease cannot be stressed, not just for the impact on affected bat species, but on its whole ecosystem-wide effects."

Klein, as an expert in and admirer of bats, made it clear to Salon that this battle — though perhaps daunting — is worth fighting because bats, quite simply, are worth saving.

"I have been completely won over by the importance of bats on our planet," Klein said. "I’m committed to helping to save them."