European bats seemingly unaffected by fungal infection.
This week, wildlife biologist Scott Darling and his small team will snowshoe up to the mouth of Vermont's remote Mount Aeolus cave, once the largest bat hibernation spot in New England. As recently as three years ago, the cave held in excess of 200,000 bats. But this year, the team will change into white protective suits and enter the cave to see if any remain.
Aeolus is one of more than 80 sites in the northeastern United States known to have been hit by white-nose syndrome (WNS), a poorly understood disease that has been devastating bat populations since it first appeared in 2006. The syndrome was named after the snowy-white fungus (Geomyces destructans) that grows on the muzzle and sometimes on the wings of afflicted bats while they hibernate (pictured above). For reasons that are still unclear, the bats rouse and fly around when they should be conserving energy; having burned their fat, they eventually starve to death.
Over the past three years, bat biologists estimate that one million bats have died from WNS in the United States, with some hibernation sites losing 90–100% of their animals. Many experts are concerned because of the bats' important role in pollination.
At Aeolus, "last year we estimate that we found between 10,000 and 20,000 dead bats on the cave floor," says Darling, who works for Vermont's Fish and Wildlife Department in Rutland. And that was just in Guano Hall, the outermost chamber of the cave. Darling and his crew don't go deeper because they want to avoid rousing the remaining bats — "and to be honest, the mortality is so disturbing", he says. "We just can't crawl through so many piles of dead bodies."
Even as biologists make their first grim ventures into US caves this year, researchers are scrambling to develop ways to counteract the syndrome and to understand its many mysteries — including why, even though the fungus has been found in European bats as well, the animals there remain healthy.
In one line of research, some groups are working to develop chemicals that could slow down or kill the fungus, but these have yet to make it out of the lab and might turn out to harm other fungi in the caves. Other teams are looking at biological controls — bacteria that could spread among the bats, live on their skin, and protect them from the fungus.
No quick fix
A vaccine could also help, although because of the challenge of vaccinating individual animals, this would probably only be practical for preserving a limited number of an endangered species — such as the Indiana bat, which has lost 30–40% of its population in the past three years.
"Unfortunately, these will take years of research, and we're operating under the assumption that we don't have that kind of time," says Jeremy Coleman, the WNS coordinator for the US Fish and Wildlife Service, who is based in Cortland, New York.
One problem is that scientists still don't know how the disease kills the bats, although many think that the fungus, which invades the hair follicles and oil glands of the bats' wings, irritates the animals and rouses them from hibernation. It is also known to damage the bats' wings, which may hamper their ability to catch their insect prey should they make it to spring. But it is possible that the fungus is an opportunistic infection, striking bats that are already ill from something else — although no other pathogen has been found.
Some clues may come from reports in the past year of white fungus on the muzzles and wings of a small number of bats in at least eight European countries. Four countries — Hungary, Germany, Switzerland and France1 — have confirmed that the fungus is Geomyces destructans, but their bats remain healthy.
Adding to the intrigue is a 1983 report that shows a picture of a German bat with powdery white substance around its muzzle2. The report mentions occasional sightings of such bats during routine winter bat surveys, suggesting that the fungus may have been infecting European bats for at least 23 years, apparently without killing them, before showing up in North America.
According to David Blehert, a microbiologist at the US Geological Survey's National Wildlife Health Center in Madison, Wisconsin, whose team first described the fungus3, the European bats may have coevolved with the fungus and developed immune resistance. They may also have behavioural adaptations that allow them to escape lethal infection; for example, European bats hibernate in small groups, ranging from 1 to rarely more than 100, whereas bats in the United States usually hibernate in groups of thousands or hundreds of thousands, ripe for rapid spread of disease.
"It will be interesting to see what the situation is in two to three years from now," says Blehert. "If the fungus they're seeing now is the same fungus that was anecdotally documented three decades ago, it does suggest that while Geomyces destructans occurs in Europe, white-nose syndrome may not."
But time is not on the side of North American bats. "Any day now I'm expecting the phone to ring with reports of new locations," says Coleman, who is particularly anxious about the disease spreading south and west (see graphic). "Tennessee, Kentucky — those are places with huge numbers of bats," he says.
Little brown bats, the predominant species in the Mount Aeolus cave, have been hardest hit, says Thomas Kunz, a biologist at Boston University in Massachusetts. And with the bats normally only producing one pup per year, the populations will struggle to come back.
"We're making predictions of extinction," he says.
Puechmaille, S. J. et al. Emerg. Infect. Dis. advance online publication doi:10.3201/eid1602.091391 (2010).
Feldmann, R. in Die Säugetiere Westfalens (eds Schröpfer, R., Feldmann, R. & Vierhaus, H. ) 107-111 (Westfälisches Museum für Naturkunde, 1984).
Blehert, D. S. et al. Science 323, 227 (2009).