The Desperate Battle Against Killer Bat Plague
by Brandon Keim, December 8, 2010, 7:00 am
It’s a postcard October morning at Kentucky’s Carter Caves state park. Sycamore and hickory have already turned orange, and the sun crests ancient Appalachian slopes against a cloudless sky. With Halloween a few days away, a life-sized Elvis dummy peeks out a visitor center window. Middle schoolers on a field trip are coming down one of the trails, preceded by their laughter.
The idyll is complete but for two details: All but two of the park’s caves are permanently shut to the public, and in the parking lot are six researchers in Tyvek bodysuits and gloves, like extras from Outbreak.
The caves are closed, and bodysuits required, because of White Nose Syndrome, a bat-killing disease more virulent than any other disease in the known history of mammals. As the children walk to their bus, I wonder if they’ll remember this morning as adults, and tell their own kids about a time when bats lived in caves. “What’s wrong with the bats?” a girl asks, her tour guides having kept the day shadow-free. “They’re sick,” I say.
My answer isn’t precisely correct. Had the girl asked Hazel Barton, a Northern Kentucky University microbiologist who’s there to sample bat hair and skin, or Brooke Slack, a state bat biologist, she would have learned that Carter Caves’ bats are being protected. White Nose Syndrome — WNS for short — hasn’t yet reached Kentucky, but its march down the cave-riddled Appalachians passed within 100 miles of where we stand, putting us squarely on the battle’s front lines.
At this point, it’s a losing battle. Bats with noses dusted by the Geomyces destructans fungus that causes WNS were seen for the first time in early 2006, in upstate New York. One year later, biologists realized that WNS could kill bats in large numbers. By 2008, mortality in major New York and Vermont hibernacula, caves where tens and hundreds of thousands of bats had wintered, was more than 90 percent. Biologists wore gas masks against the stench of rotting bodies. Bones cracked like popcorn under their feet.
By the end of last winter, G. destructans was found in 14 states and two Canadian provinces, and at least a million bats were dead. In August, a high-profile Science study gave computationally modeled meaning to all those dead-bat piles. The little brown bat, more common than any other in North America, the furred star of most every attic and open-window encounter, so numerous as to be considered pests, would be extinct in 20 years in the eastern United States. If by some unexpected miracle WNS mortality dropped from over 90 percent to 5 percent, they might make it to the century’s end.
That essential prognosis applies to at least three other cave-dwelling, hibernating bat species, and probably more, though one-by-one tabulations tend to obscure the potential of WNS to annihilate an entire manner of animal being. In sheer magnitude, WNS threatens to dwarf the demise of plains bison or passenger pigeons, the historical benchmarks of American animal collapse. The closest comparison is Chytridiomycosis, a fungal disease now scouring amphibians from much of the planet.
Yet even as the reality of WNS has emerged in the popular press, public and policy reaction has been muted. Awareness and concern exists, but at a fraction of what would likely be displayed if, say, half of America’s waterfowl were about to vanish.
Bat conservationists tend to blame this on bats’ unfair and untrue reputation as rabies-ridden, hair-tangling rodents. A more fundamental problem, however, is that bats are generally absent from everyday awareness. Most specialize in eating insects at night in the air, an ecological niche both staggeringly enormous and out of sight. Their taxonomic order, Chiroptera — more closely related to primates than rodents — contains more mammal species than any order except rodents, yet most people have never seen a bat up close.
Several thousand hibernate in the old saltpeter mine where Hazel Barton and Brooke Slack and their assistants go. At this point in the season, they’ll fly out at night for a last few pre-winter meals. In the daytime they sleep, clinging to walls and cuddling for warmth and companionship.
Barton, a lifelong spelunker with rare expertise in cave microbiology, is interested in fungi that grow naturally on bat skin. By the glow of headlamps the researchers pluck bats from the ceiling with practiced efficiency, swabbing their skin and clipping tufts of hair from which fungal DNA will later be extracted. Slack examines the wings, looking for any signs of the dreaded disease.
This early in the season, it’s extremely unlikely that G. destructans growth would be visible. But it’s always possible that some spore-carrying survivor from one of West Virginia’s WNS-afflicted colonies arrived this season, scars on its wings portending potential doom. The presence of G. destructans was confirmed in West Virginia’s largest hibernacula last winter; it also reached Tennessee, Missouri and Oklahoma. Barton and Slack were sure it would reach Carter Caves, as well. Their fears survived for another season.
Despite the researchers’ care, the bats start to wake, roused by noise and light and even the ambient temperature difference of our bodies. By the time Barton finishes, many are aloft, circling with the speed and agility of swallows. Their cries reverberate down the narrow hall. Others remain hanging, swaying every so slightly, just enough to make it feel like the walls are pulsing. It’s as if the entire cave is alive.
As we hurry out, I ask Barton whether she thinks these bats will stay WNS-free, if they have a chance. Grimacing, she shakes her head.
Over a few months of taxi and bar conversations about WNS, most people’s instinctive response was to imagine a treatment, a drug of some sort, something that can be sprayed on bats to kill the fungus and control the disease.
It’s a noble response, rooted in an elbow-grease, can-do spirit and the historical success of relatively straightforward conservation measures like habitat protection and captive breeding, plus an abiding American faith in both medication and technology. Indeed, several groups of researchers, including Hazel Barton and her collaborators, are working on anti-WNS treatments. But if finding a compound that killed G. destructans in a petri dish was enough to stop the outbreak, it would already be over.
In laboratory tests, drug store antifungals like Tinactin and Lamisil kill G. destructans just fine. They’re also neurotoxic endocrine disruptors that kill bats, and even at low, sub-lethal doses would tilt the balance towards extinction. It’s not hard to do. Unlike most small animals, bats live for decades and reproduce slowly, perhaps because — until WNS — survival was generally assured upon reaching adulthood. There was little need for replenishment. Healthy populations of little brown bats grow at an infinitesimal annual rate of about .008 percent.
Unless a WNS treatment destroys G. destructans while staying on the safe side of that threshold, it will simply substitute for the disease. And if researchers find a physiologically safe compound, it needs to be ecologically safe as well, leaving unharmed the thousands of other fungal species that are the foundation of cave ecosystems.
It’s not a trivial concern. When Fusarium solani fungus started to eat the 17,000-year-old cave paintings in Lascaux, France, it was easily eradicated with chemicals. Two years later, an even worse fungus sprouted on the pigments, apparently unleashed from environmental insignificance by the treatments. The same could happen to bats.
After all this, should some safe and balanced compound be found, researchers would need to treat every single bat in every last crack and crevice, all winter long, at outbreak sites. It’s conceivable, but would be so logistically challenging and labor-intensive that even successful treatments represent a stopgap measure.
“Is it possible? Theoretically, yes. But the best-case scenario is to slow the spread down, and maybe to protect one very, very special site,” says Pennsylvania Game Commission biologist Greg Turner. “Even though I’m doing these treatment experiments, I don’t put a lot of hope in finding some miracle cure. There’s just too many problems.”
Kentucky is on the front lines of WNS, but Pennsylvania is a central battleground. The disease arrived in 2008, and has since spread through the state’s eastern hibernacula, with death counts ranging from 80 percent to 99.9 percent. Western Pennsylvania held out longer, but I met Turner as he was driving to Laurel Caverns in the state’s far southwestern tip, where WNS arrived last winter.
Together with fellow Commission biologist Cal Butchkoski, Turner is responsible for Pennsylvania’s bats. On this morning he’s wearing a T-shirt reading, “Bats Need Friends Too,” over which he’ll later button his Game Commission uniform. For years he and Butchkoski have traveled the state year-round, counting bats in hundreds of caves and mines, painstakingly detailing their movements and habits.
When WNS hit, they already knew what happened in New York, and were ready — not to stop the disease, though cave closures and decontamination protocols probably slowed its accidental spread by human cave visitors, but to study it.
As a result, Pennsylvania has become a giant WNS laboratory. Turner and Butchkoski make observations and gather samples used by dozens of researchers, especially Hazel Barton and Bucknell University bat biologist DeeAnn Reeder. Together they’re studying a myriad of basic biological questions that need to be answered before WNS can be understood, much less stopped. And of all their questions, none is more basic than this: Why do the bats die?
Portrait of a Killer
It may seem strange to still have this question. There is, after all, no shortage of dead bats to study. But the WNS outbreak cast into sharp relief just how much remains to be learned about the basic biology of the everyday world.
In bats, for example, there’s no such thing as a blood test of the sort that’s routinely administered to people and even our pets, giving a quick chemical and immunological profile of health. The bat immune system is, in Barton’s words, “a blank sheet of paper with a black box in the middle.”
At the ecological level, what many bat species eat, and even where they live for certain parts of the year, is almost as mysterious. And compared to fungi, bats are well-understood. Barton and Reeder were thrust into the forefront of WNS research not only because they’re good scientists, but because they were among the few people studying relevant questions when the disease hit.
Out of all this uncertainty, a picture of WNS has slowly emerged. At its center is G. destructans itself, which had not been identified before the outbreak. Like Batrachochytrium dendrobatidis, the fungus responsible for chytridiomycosis in amphibians), it violates what had been a cardinal rule of fungal infections: They’re not fatal. Its unexpected nature is one reason it took several years for researchers to generally agree that G. destructans causes WNS.
Leading the characterization of G. destructans were researchers from the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wisconsin. They sequenced the fungi’s genes, placing it within the otherwise innocuous Geomyces clade, found widely in soil — “myces” signifies fungus, “geo” means “of the Earth” — and describing its physical characteristics, in particular its telltale sickle-shaped spores. They also named it destructans, a straightforward and accurate appellation.
The bats’ eponymous white noses are just visible spore growth. The real damage occurs below. G. destructans lives on bat skin, invading hair follicles and sebaceous glands, forming pockets on the surface of exposed wings, breaking through into the epithelium beneath. There it breaks down connective tissue and muscle and nerves into digestible nutrients. Under a microscope, researchers liken G. destructans mycelium to spaghetti wriggling into meat. Another resemblance is the demon worms that consume animal flesh in Hayao Miyazaki’s Princess Mononoke.
How this progresses at a cell-by-level level is not known. At the other end of the scale, the chain of transmission between bats — whether it spreads in winter or fall or spring, if animals of particular life stages or habits are the primary vectors — is also uncertain. Also undetermined are the exact origins of G. destructans.
It may have come on a tourist’s boot or cargo stowaway bat from Europe, where G. destructans, or something very much like it, has subsequently been found, but in the absence of disease. Their apparent resistance suggests that modern European bats are descended from survivors of a prehistoric WNS epidemic, and G. destructans is “like smallpox arriving in the New World,” says Reeder. But it’s also possible that American G. destructans differs subtly from European, with some single, as-yet-unspecified mutation just happening to produce a skin-digesting enzyme.
Whatever its origins, G. destructans thrives in the cold favored by cave-dwelling, hibernating bats, which during hibernation cool their bodies to ambient temperatures. Among hibernators in general, this usually involves shutting down energy-intensive immune systems. “Here comes this cold-loving fungus, and it’s found immune-suppressed animals. They’re like HIV patients. It’s a perfect storm,” says Reeder.
With the help of temperature-recording sensors affixed to bat bodies and thermal cameras in caves, Reeder and other researchers have found that little brown bats, which briefly wake from hibernation every few weeks when healthy, rise every few days when infected. She suspects that arousal is a form of immune system “rebooting,” and that bats with WNS are trying to fight the disease.
Another proposed explanation comes from the USGS researchers, who note the importance of bat wings, which G. destructans reduces to the consistency of perforated tissue paper, to maintaining water balance and homeostasis. Autopsies of WNS-killed bats have found many to be so dehydrated that their tissues stick to researchers’ fingers. According to this hypothesis, infected bats wake, and can die, from thirst.
Both explanations could be right. The fungus may also release toxins, or open holes for secondary bacterial infections. Whatever the pathological constellation, waking from hibernation requires a rise in body temperature from 40 degrees to more than 100 degrees Fahrenheit. Stoking biological furnaces burns quickly through the bats’ fat reserves. Looking for food, perhaps, or disoriented by dehydration, many fly outside, giving rise to another defining phenomenon of the disease: Bats flying out of caves in daylight, one by one for weeks on end, dying on the landscape in the middle of winter.
Amidst this carnage are a few cautiously optimistic notes. Field observations and Reeder’s work with captive bats suggests that WNS virulence varies by cave microclimate. Reeder, whose lab whiteboard is filled from top to bottom with the upcoming winter’s experiments, recently installed a set of environmental chambers that provide fine-tuned control over temperature and humidity for bats inside. If cold and dryness moderate the disease, she and the Pennsylvania biologists will try to manipulate real-world environments, sinking air shafts into hibernacula to create pockets of safety.
Other biologists, including former New York Department of Environmental Conservation biologist Al Hicks, have proposed designing “artificial hibernacula,” perhaps in repurposed World War II ammunition bunkers, where transplanted colonies of bats could be monitored and treated.
“You have no choice but to do everything you can do,” says Turner. “When you think of yourself as a conservationist in any way, it’s not to throw your hands up and say, ‘We’re fucked.’ There’s always a glimmer of hope somewhere.”
A World Without Bats
Cal Butchkoski, the other Game Commission bat biologist, echoes Turner. “How do you keep from despair? You have to maintain some hope,” he says. But a note of fatalism tinges the voice of Butchkoski, a thoughtful, soft-spoken man whose bat labors stretch back two decades, whose backyard bat colony is still big enough for him to have a mosquito-free beer on summer evenings. “There’s just so much we don’t know.”
On a crisp fall night in Amish farm country outside State College, Pennsylvania, Butchkoski is visiting a hibernacula where WNS was detected last year. He thinks that about half the bats died, though the count’s not official. On this night, he and three assistants are seeing what’s still alive. With plastic sheeting they seal the cave entrance, a nondescript-looking crevice in a streamside hollow, then cut a window-sized hole. Into the hole goes a harp trap, named for its resemblance to the musical instrument. Bats will hit the strings, and fall into a padded bag at the bottom.
Having set the trap, the researchers walk back to their trucks, and settle into folding chairs to wait. A bat detector relays a static hum from the cave entrance. A full moon rises. I think on a question implicit in the epidemic: What does it really matter if bats die?
There are different perspectives on this question.
One is at the level of organismal empathy. Infected bats undoubtedly suffer, perhaps in a manner people typically associate with larger, more charismatic animals. “It wouldn’t surprise me that bats have some sort of rudimentary language,” Bill Elliott, a bat biologist with the Missouri Department of Conservation, told me. “They have sophisticated social interactions. We think our big brains are the ultimate, but going in the other direction is just as good.”
Beyond the organismal level is that of species, not just one but a slew. The little brown bat has received the most attention, but the Eastern pipistrelle, Northern long-ear and endangered Indiana bat all appear equally vulnerable. Somewhat more resistant, but still imperiled, are big brown and small-footed bats. Those six species happened to be first in line in the northeast. In the past year, G. destructans was found in three southern species — the cave myotis, gray bat, and southeastern myotis. It remains to be seen how WNS will progress in them.
Altogether, more than half of North America’s 45 bat species may fit the cave-dwelling, hibernating WNS victim profile. And if one takes seriously the notion that the natural world is a collective treasure, a living museum several billion years in the making, then bats represent a whole wing of it. Losing half of them in North America is a bit like losing half our jazz musicians, or abstract painters, or novelists. Something unique and unreplicable will be gone.
The same argument extends to certain cave systems, especially in the southeast, where entire ecologies of cave-adapted animals rely on guano as a foundational nutrient source. “The consequences of losing the guano could be dire. It could mean these systems eventually run down,” said Elliott.
Not everyone shares conservationist sentiments. But there’s a utilitarian argument as well, short and sweet. Bats eat bugs. Lots of them. Little brown bats famously eat half their body weight in bugs each night, more if they’re nursing. Many of those insects eat crops.
The bottom-line value of their pest control is methodologically difficult to compute, but Boston University bat ecologist Tom Kunz made an informative try several years ago. In an eight-county region of south-central Texas, where Mexican freetail bats eat cotton bollworms and corn earworms, he calculated that bats save farmers roughly $740,000 annually — about one-eighth of total harvest value — in prevented crop damage and reduced pesticide treatments.
Early in the summer, before the region’s farmers typically start to use pesticides, the labor of each individual freetail was worth about $.02 per night. In a region where airborne bat densities are so great as to be visible on Doppler radar, it adds up.
Mexican freetails are probably safe from WNS, but Kunz’s figures are instructive. Some variant likely holds just about everywhere bats live. And contrary to the conventional expectation that evolution and ecology will find something else to do the bats’ job, their niche will almost certainly stay empty in any human-relevant timeframe. Nocturnal airborne insects are the sole province of bats, a food source they’ve exploited so completely and efficiently over the last 50 million years as to be without competition.
“There are people who say, ‘Well, birds will do better.’ No. They’re not going to eat the nocturnal insects,” says Reeder. And should a few bats prove genetically resistant to WNS, in sufficient numbers that some other environmental circumstance doesn’t finish them off, it will still take hundreds or thousands of years to recover.
The agricultural threat alone makes it all the more unreasonable that WNS researchers have been given a pittance of federal support.
The National Science Foundation has essentially ignored the disease. The U.S. Fish and Wildlife Service, through which most WNS research and management is coordinated, spent $2.4 million on the disease last year, or slightly less than it expects to save through upgrades to departmental e-mail and data processing. Congress gave an extra $1.9 million in 2010, but that may have been a one-time event.
As of early November, the Department of the Interior’s omnibus appropriations budget, slated for a December vote, contained a $5 million WNS funding request. In this deficit-sensitive moment, however, such “earmarks” are an unpopular proposition.
Winifed Frick, a University of California, Santa Cruz bioinformaticist who with Kunz co-authored the Science paper on imminent little brown bat extinction, described meeting in October with the legislative aide of one prominent Senator.
“She said, ‘We’ve been asked to trim the budget. Unless you can show how this is going to help blue-collar jobs, I don’t know how this is going to get through,’” said Frick. “It’s a tough budget year. This would be considered an earmark. I get it. But it’s frustrating when $5 million is not a lot in terms of appropriations, and would make a huge difference in terms of our project.”
It should be noted that Butchkoski’s three technicians on the Amish farm count are seasonal contract workers and fit any non-industrial definition of blue-collar labor. But as they check the trap, thoughts of funding and politics are far away. The night’s haul is four northern long-ears. They submit graciously to Butchkoski’s inspections, opening their mouths in brief protest before settling down on the technicians’ thumbs. Their wings prove mercifully free of disease.
“I never thought I’d be so happy to see four northern long-ears,” he says. “Now we know they’re here. Thankfully, they’re still here.”
The Start of Winter
On a rainy mid-November morning, Hazel Barton and Greg Turner and DeeAnn Reeder’s students hike to the Durham iron mine outside Bucks County, Pennsylvania. First excavated by Winnebago Indians, then by colonial settlers, it was abandoned in the 19th century and eventually became home to about 8,000 bats.
When WNS hit last year, the researchers scrambled to test an antifungal compound that had shown laboratory promise. By the time they started, though, the outbreak was well underway, and the cages they built had holes. When the researchers came back two months later, the cages were empty, and the bats a brown sludge of decay on the floor. Dismaying results, but inconclusive: Maybe it would have worked if they’d started sooner, or if the bats hadn’t escaped.
The researchers have arrived earlier this year, with several new compounds and more reliable equipment. After crawling down a series of sloping, rubble-filled tunnels, they reach a central hallway. On one rust-colored wall, some long-ago vandal has spray painted, “Land of the Bats.”
Maybe a thousand bats are still left. Reeder’s students pick them from the walls, placing some in coolers for transport back to her lab, where they’ll live this winter. Others go into plywood treatment cages. Barton is secretive about the compounds, but allows that one is carvone, the candidate from last year. Three others are derived from antifungals identified by her research as produced naturally on bat skin.
Will the treatments work? “We’ll find out when come back in the spring,” says Barton.
Many other questions may also be answered by then. How will the southern and western spread of G. destructans play out? Will it be less virulent in warmer climes, in new species with different habits? Will some prove resistant, but carry it even further? Will it cross the Great Plains? Will it spread to the Great Lakes region, where it will almost assuredly be as destructive as in the northeast? In the northeast, will there be signs of resistance?
Asking bat researchers about this winter, two phrases keep coming up: “Holding our breath” and “Waiting for the other shoe to drop.”
Several of Barton and Reeder’s compounds are aerosols, contained in bottles beneath the bats’ cages. To help with dispersal, they’ve been mixed with oils, aromatherapy-style. Improbably, Durham Mine fills with the scent of almonds. Barton bounds back and forth, peering into the cages. For all her earlier caveats about the limitations of treatment, her voice is full of excitement. As we leave, the cages recede into darkness.
On the drive up, Barton described how, during the trial’s first run, she’d expected to return to cages full of healthy bats, with others clinging to the outside, trying to get in. On the ride back, I ask if she still does.
“If I didn’t have that hope, I wouldn’t be doing this,” she says.
Images: 1) Indiana bat inspected by Brooke Slack at Carter Caves state park, Kentucky. 2) Little brown bats in Laurel Caverns, Pennsylvania. 3) A little brown bat with White Nose Syndrome in a limestone mine near Rosendale, New York. 4) Northern long-eared bat examined on a far near State College, Pennsylvania. 5) Little brown bat in a treatment cage in Durham Mine, Bucks County, Pennsylvania. 6) Treatment cage in Durham Mine. All photographs by Brandon Keim.
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