If you like organic produce and hate mosquitoes, you should care about white-nose syndrome.
The fungal epidemic has killed about 6 million bats in 26 U.S. states and five Canadian provinces since 2006, pushing several species near the brink of extinction. Losing any species is bad, but bats are especially helpful to humans. One little brown bat can eat hundreds of mosquitoes per hour on summer nights, and insect-eating bats overall save U.S. farmers an estimated $23 billion per year by eating crop pests like moths and beetles. Many insects simply avoid areas where they hear bat calls.
But while the outlook is still bleak for North America's bats, there are finally a few glimmers of hope. In one of the brightest glimmers yet, scientists released several dozen bats in Missouri on May 19 after successfully ridding them of white-nose syndrome. The disease often wipes out entire bat colonies in a single winter, and it has long defied our best efforts to control it, so that's a pretty big deal.
"We are very, very optimistic" about this new treatment, says U.S. Forest Service researcher Sybill Amelon, one of the scientists who helped heal the infected bats. "Cautious, but optimistic."
White-nose syndrome (WNS) is caused by a cold-loving fungus, Pseudogymnoascus destructans, that attacks bats while their body temperatures are low during hibernation. It's named after the telltale white fuzz that grows on the noses, ears and wings of infected bats. After its 2006 debut at a cave in New York, the fungus is now obliterating bat colonies from Ontario to Alabama, threatening to wipe out some species forever. Scientists think P. destructans invaded North America from Europe, where hibernating bats seem resistant to similar fungi. It's not clear how it crossed the Atlantic, but a leading theory suggests traveling spelunkers unwittingly carried spores on their shoes, clothes or equipment.
A lab culture of P. destructans, which causes bats to wake up too early from hibernation and starve. (Photo: Raudabaugh DB/Wikipedia)
From saving bananas to saving bats
So how did the Missouri bats survive? The researchers enlisted a common bacterium, Rhodococcus rhodochrous (strain DAP-96253), that's native to an array of North American soils. Humans already use R. rhodochrous for a few industrial purposes like bioremediation and food preservation, and microbiologist Chris Cornelison of Georgia State University found its bat-saving potential on a whim.
"Originally, we were investigating the bacteria for various industrial activities," Cornelison tells MNN. "In some of those earliest experiments, in addition to delaying the ripening of bananas, we noticed the bananas also had a lower fungal burden. I was just learning about white-nose syndrome at the time. But I thought that if this bacterium could prevent mold from growing on a banana, perhaps it could prevent mold from growing on a bat."
Apparently it can. And while another team of researchers also recently identified bat-wing bacteria that suppress WNS, Cornelison has shown that R. rhodochrous can help bats recover without even touching them. That's because the bacteria produce certain volatile organic compounds (VOCs) that stop P. destructans from growing. That's a key detail, since applying any medicine directly to entire colonies of hibernating bats is inefficient at best. It's also not easy to find a treatment that kills P. destructans without also killing harmless native fungi or otherwise disrupting the cave ecosystem.
Cornelison began studying R. rhodochrous and WNS in 2012, along with Amelon and wildlife biologist Dan Linder, also of the Forest Service. Backed by funding from Bat Conservation International, he published a study about R. rhodochrous last year, describing the discovery as "a major milestone in the development of viable biological control options" for WNS. Since then, he has worked at caves in northeastern Missouri with Amelon and Linder to investigate how these VOCs affect bats with WNS.
A few species of Rhodococcus bacteria are pathogenic, according to the CDC, but the majority are 'benign soil inhabitants.' (Photo: Centers for Disease Control and Prevention)
A wing and a prayer
"The bats were treated for 48 hours, and they were exposed in the same areas where they hibernate," Amelon says. "We put the bats into small mesh containers where they're comfortable. Then we put them inside a cooler, and placed volatiles in the cooler but not in direct contact, so the volatiles filled the air."
The researchers did this with 150 bats, about half of which were released May 19 at Mark Twain Cave in Hannibal, Missouri. Those survivors — mostly little brown bats, but also some northern long-eareds — are seemingly cured of WNS, with no detectable signs of the fungus or the disease, and they all took test flights before the release. Still, Amelon adds, it's too soon to know if they're really out of the woods.
"It's a complicated process with this disease," she says. "These guys could certainly be considered survivors of this winter. But we are not sure if they have any long-term benefits, or whether they could redevelop the disease next season. Prevention is much better than a cure in this case."
Cornelison agrees, noting that rehabbing and releasing bats isn't the long-term plan. Now that they've shown what R. rhodochrous can do, the real goal is to stop WNS before it gets out of hand. That will require more research, he adds, into how exactly the treatment works and how broadly it might protect healthy bat colonies. "We think it has the highest potential for prevention," he says. "We're exploring a number of different application technologies that target the spores. If you can prevent the spores from germinating and proliferating, you can greatly reduce transmission and disease severity."
Researcher Sybill Amelon holds a recovered little brown bat before its release on May 19, 2015. (Photo: Bat Conservation International)
The researchers decided to release half of the recovered bats now because May is when they would normally emerge from hibernation. Some of the treated bats have too much wing damage to be released, but some healthy ones are also being kept for further study of their long-term recovery. The released bats are wearing ID tags on their forearms (pictured above), so researchers will be keeping an eye on their progress, too. "We still have a lot of data to analyze," Amelon says.
There hasn't been much good news about WNS in the past decade, so breakthroughs like this are cause for celebration. But the epidemic is still spreading ferociously across the continent, and with lots of physical and ecological variables at bat caves, it's unlikely a silver bullet will be found. Instead, Cornelison says, we'll need a deep arsenal of science to fend off this fungus.
"It's very promising, but what we need are a variety of tools to take an integrated disease-management approach," he says. "They use a lot of diverse habitats and different hibernacula, so we may need to use a lot of different tools. And the more tools we have, the more flexibility we have."