The past decade has been historically bad for North America's hibernating bats. White-nose syndrome, a fungal disease first reported at a New York cave in 2006, is now in 33 states and five Canadian provinces, where it has killed millions of bats, decimated major colonies and even threatens some species with extinction.
The invasive fungus behind white-nose syndrome (WNS) was unknown before 2006, but scientists have begun learning more and more of its secrets lately. Once seen as virtually invincible, it has proven susceptible to certain bacteria in recent years. And now a new study hints at a potential "Achilles' heel" for the fungus: ultraviolet light.
A map showing the spread of white-nose syndrome from 2006 to 2017. (Image: whitenosesyndrome.org)
The fungus, Pseudogymnoascus destructans, is a cold-loving species that can only infect bats when their body temperatures drop during hibernation. It's vulnerable to heat, but given the impracticality of heating up bat caves across the continent, biologists are looking for simpler ways to fight the epidemic — and fast.
"WNS represents one of the most severe wildlife diseases ever recorded," the researchers write in the journal Nature Communications. Its explosive spread across North America has raised widespread alarm about the survival of native bat species, many of which play important ecological and economic roles by eating insects. The fungus awakens bats from hibernation too early, causing them to burn through their fat reserves and potentially starve to death before spring arrives.
P. destructans is thought to be an invasive species from Eurasia, where it evolved alongside Eurasian bats for millions of years, giving those species time to develop defenses. People may have accidentally carried its spores to North America, possibly on spelunking gear, allowing it to capitalize on a continent full of defenseless bats.
As the fungus continues to spread, scientists have been poring over its genome, along with those of related fungi, in hopes of exposing any weakness.
A light touch
A lab culture of P. destructans, which can fatally disrupt the hibernation of bats. (Photo: Raudabaugh DB/Wikipedia)
In the new study, researchers from the U.S. Forest Service, U.S. Department of Agriculture and the University of New Hampshire compared the genome of P. destructans with six closely related fungi. They noticed that P. destructans lacked a key enzyme for repairing DNA damage, so they hit the fungus with a variety of DNA-damaging agents — including ultraviolet light. UV light is already used to diagnose WNS infections, causing the fungus to shine orange, but researchers tested out different wavelengths and intensities of UV light for the new study.
That revealed "a potential Achilles' heel of P. destructans," the study's authors write, "that might be exploited for treatment of bats with WNS." A low-dose exposure of UV-C light resulted in a roughly 15 percent survival rate for the fungus, while a moderate-dose exposure led to less than 1 percent survival. This only requires a few seconds of exposure from a hand-held UV-C light source, the researchers note.
"It is unusual that P. destructans appears to be unable to repair damage caused by UV light," says lead author Jon Palmer, a research botanist for the U.S. Forest Service's Northern Research Station, in a statement. "Most organisms that have been found in the absence of light maintain the ability to repair DNA caused by UV light radiation. We are very hopeful that the fungus' extreme vulnerability to UV light can be exploited to manage the disease and save bats."
To the bat cave
The next steps of figuring that out are already under way. Daniel Lindner, a research plant pathologist with the Northern Research Station and corresponding author on the study, is leading follow-up research to see if UV light can help little brown bats recover from WNS, according to the Forest Service.
North America has dozens of small, insect-eating species like the little brown bat, just one of which can eat 60 medium-sized moths or 1,000 mosquito-sized flies in a night. Bats also save U.S. corn farmers about $1 billion per year by eating crop pests, and their value to U.S. agriculture overall ranges from $3.7 billion to $53 billion per year.
"This research has tremendous implications for bats and people," says Tony Ferguson, director of the Northern Research Station. "Bats play a key role in the health of forests as well as the production of food in the United States, and developing an array of tools with which we can treat bats for white-nose syndrome is important to preserving these very important species."