An Experimental Treatment Shows Promise In Helping Bats Weather A Deadly Fungus
In Pennsylvania, White-nose Syndrome has wiped out about 99 percent of the adult little brown bat population, but an experimental treatment is starting to pay off.
Bats are infected with the disease, caused by an invasive fungus when they enter their winter hibernaculum.
In late summer 2018, scientists from the Pennsylvania Game Commission and researchers from Temple and Lock Haven universities sprayed the inside of an abandoned brick and concrete railroad tunnel where bats hibernate with the chemical compound polyethylene glycol 8000. Known as PEG, it’s approved by the FDA for consumption by humans, and is non-toxic to mammals.
“The way the substance works for us is it’s what we call an osmoticum,” said Greg Turner, state mammalogist with the Pennsylvania Game Commission. “What that means is it really grabs water and holds onto it. Fungi are typically very susceptible to water stress.”
The fungi spores that cause White-nose are coated with the compound, and won’t germinate.
When the first bats enter the tunnel to hibernate, typically females, they crawl around on the spores inactivated by PEG. Bats that have visited other infected sites, typically males looking to mate, bring the active fungus with them later.
The delay of reintroducing the fungus to the tunnel slows the spread of the disease. When the bats leave the tunnel in the spring, it takes a few weeks for them to clear themselves of the fungus.
The tunnel, an abandoned railway passage known as the Sabula tunnel in Clearfield County, has been sprayed each summer since, as bats reinfect themselves each year as they return.
The experimental treatment is still in its early stages.
“This will be the third year that we’ve applied for it,” he said. “And at some point, we’ll try and figure out if the effects actually last. So we’ll stop treating it to see how quickly it resumes the disease severity levels before treatment.”
Turner said after analyzing two years of data, the results are encouraging:
- All of the little brown bats in the Sabula tunnel were still infected by the fungus, but the treatment reduced how much disease the bats got by an average of 65 percent over those 2 years.
- The treatment reduced how many big brown bats got the disease, as well as how much disease they got. Big brown bats are another common species in the Sabula tunnel.
Mike Scafini, endangered mammal specialist with the Pennsylvania Game Commission, said there has been a slow and steady increase of little brown bats in the tunnel from when they first began treating it. Their numbers have gone up by a third.
“This past winter, we found 169 bats at this site, 85 of which are little brown bats, which is of particular interest to us because they are now endangered in Pennsylvania,” Scafini said.
An Epidemic That’s Decimated Bat Populations
According to the PA Game Commission, the fungus that causes White-nose Syndrome, Geomyces destructans, was first detected in Pennsylvania in 2008, and the first cave bat mortalities were recorded in 2009.
Millions of bats have been infected.
“The fungus actually digests live skin cells,” Turner said. “So their wings are the primary organ that is being affected, and it causes thousands of small wounds.”
Turner says bats periodically come out of hibernation in the winter, warming up from 40 degrees to their operating body temperature of 101 degrees. White-nose Syndrome causes that to happen about twice as often. They burn through the fat reserves they stored for energy halfway through the winter.
“Then they were either going to starve to death or exit [the hibernaculum] and freeze to death,” Turner said.
He said an electrolyte imbalance can cause infected bats to fly into things, or even fly out of the cave or tunnel in the daylight, only to fall prey to raccoons or hawks.
The PEG treatment has expanded to a few other sites, including most recently, tunnels in eastern Ohio.
Originally it was applied only to man-made structures until it could be determined if PEG impacts bacteria, other fungi, or even little salamanders at the sites. It doesn’t, so a commercial cave is now also being treated.
Other Promising Treatments
Site manipulation is another method of treating these hibernation sites. In the Sabula tunnel, the little brown bats seem to prefer the center of the ceiling, where temperatures in the winter could average 38 degrees. Greg Turner says that it is colder than bats were known to prefer before White-nose Syndrome.
“The bats are actually selecting these colder environments because that helps them save energy,” he said. “And that’s a mechanism they use physiologically to stay in hibernation longer. But it also helps them with the fungus, as the fungus grows slower, the colder it gets.”
To get hibernaculum sites to the temperatures that bats prefer, Scafini said they have created additional openings, or made cold air dams, like earthen berms, in front of the openings to keep the cold air inside.
“It seems so far that at the few sites we’ve tried this out that it does indeed seem to be working,” Scafini said. “One site in Blair County has increased from seven bats to 81 bats since implementing this in 2016.”
Turner said it’s important that juvenile bats join these bat colonies, otherwise there will just be a slow decline of the remaining adult survivors.
“Our goal is to provide a few select sites that we can treat through any means possible that we know of, and just really help protect the species from going extinct,” Turner said. “Once we get that stabilization and slight increase, we’re hoping that these sites will help fuel and rekindle a lot of the surrounding sites out there.”
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