Last week U.S. state and federal wildlife agencies announced that white-nose syndrome—a deadly fungal disease that has killed more than six million hibernating bats in the eastern U.S.—has made a 2,000-kilometer jump across the country from eastern Nebraska to Washington State. There it is known to have infected and killed at least one bat in the small town of North Bend, 48 east of Seattle.
How the disease made such a vast leap remains a mystery. To try solving it, a group of scientists led by the U.S. Geological Survey’s National Wildlife Health Center (NWHC) in Madison, Wis.—one of the nation’s top wildlife disease laboratories—is looking to DNA for clues. “Genetic testing may allow us to create a map that helps us understand how the Washington State bat became infected with P. destructans,” says David Blehert, a molecular biologist at the NWHC and leader of his lab’s white-nose syndrome research.
Pseudogymnoascus destructans is the slow-growing fungus that causes white-nose syndrome. It thrives in cold, damp cave environments, making cold-adapted hibernating bats an easy target. As bats hang dormant from cave ceilings, P. destructans invades their skin tissues. It causes lesions and often the characteristic “white nose,” a visible accumulation of powderlike white fluff on a bat’s muzzle. Internally, P. destructans causes problems that disrupt hibernation and lead to dehydration, starvation and eventually death. Wildlife experts say it poses no known risks to humans.
The fungus is not native to the U.S. Most likely it arrived via human trade or transportation from Asia or Europe, where it is believed to have originated, says Jeremy Coleman, U.S. Fish and Wildlife Service national white-nose syndrome coordinator. Bats can transmit P. destructans among themselves and the spores can persist in caves for years, infecting many generations of the animals. But Coleman says humans are the prime mode of transmission suspected in the case of the North Bend bat. Blehert agrees: “To date, white-nose has spread following a particular pattern across the East up to a line in the Midwest, and then, boom! It’s suddenly 1,300 miles west in Washington State.”
Whereas this jump could have hypothetically occurred in “bucket brigade” fashion between several bats, Blehert says it is more likely a human visitor to an infected cave carried P. destructans to the Northwest on contaminated clothing or gear, possibly in “a clod of dirt in the sole of their hiking boot.”
An international team of scientists recently discovered that white-nose syndrome is widespread in parts of Asia, where bats appear to be more resistant to its harmful effects—as they are in Europe. This could be due to genetic differences among species, but also might be related to variations in gut bacteria, immune responses or nuances in hibernation, says Joseph Hoyt, a graduate student in Earth and marine sciences at the University of California, Santa Cruz, who led the Asian white-nose syndrome study. Environmental conditions such as temperature and humidity can also affect the syndrome’s virulence. Bats in warmer, more humid habitats tend to experience higher rates and more severe cases than those in cooler, drier places, says Hoyt, who is currently in China collecting P. destructans samples for genetic testing.
Although running genetic analyses on a fungus might sound unusual, it is not a novel idea: Today, wildlife disease research goes beyond diagnosing illness. When disease outbreaks strike, unlocking pathogens’ genetic codes may provide insight into how they spread—and how to stop them from causing further infection. Just last year, scientists at the NWHC focused their attention on studying avian influenza DNA, which caused a devastating outbreak that killed hundreds of wild migratory birds and more than 48 million chickens and turkeys across the U.S. West and Midwest from December 2014 to June 2015. Although research is still underway, experts say both human actions and bird migration appear to have contributed to transmission.
The recent development of next-generation or “high-throughput” sequencing technologies have allowed for faster, less expensive and often more reliable genomic testing of pathogens such as viruses, bacteria and fungi. But even with the best genetic technologies, decoding and comparing the genomes of various samples of P. destructans could take a long time: Whereas viruses’ nuclei contain thousands to tens of thousands of nucleotides, fungi nuclei can contain millions.
Experts hope to determine how white-nose syndrome traveled to Washington—the 28th state where it has been detected—sooner rather than later. “We have a lot of concerns about the discovery of this single bat: One bat found, was found with advanced stage of the disease,” Coleman says. “Bats do not succumb to that level of disease unless the fungus has been present for several years.”
Because white-nose syndrome was first diagnosed in North American bats in 2006, federal and state wildlife agencies have poured more than $50 million into disease research. Some scientists have been working toward treatments, but there’s no effective cure. Instead, wildlife management agencies rely on a containment strategy, closing caves and promoting a decontamination protocol for cave visitors in a bid to prevent humans from spreading the fungus.
Scientists are not the only ones on the front lines of the U.S. white-nose syndrome outbreak: Spelunkers are also helping to quell the spread of the disease. Jennifer Foote, white-nose syndrome liaison with the National Speleological Society (NSS), a group of caving enthusiasts, says her organization’s members have directly assisted wildlife management agencies in educating the public about the disease and conducting research. Additionally, the NSS has donated more than $115,000 in funding for 22 white-nose syndrome research grants to date.
Although NSS supports bat conservation and research, some efforts to control white-nose syndrome have been a major headache for cavers, Foote says. “Some members have quit caving temporarily or permanently. [White-nose syndrome] has made it more stressful than relaxing to go out and enjoy nature.”