SOUDAN— Officials at Lake Vermilion-Soudan Underground Mine State Park, this week, announced the news they have long dreaded— that hundreds of bats in the park have apparently died of white-nose syndrome (WNS) so far this winter.
The fungal disease, first identified in the U.S. in 2007, has decimated bat populations in eastern North America over the past several years. Bat researchers first documented the presence of the pathogen, known as Pseudogymnoascus destructans, in the Soudan Mine in 2013, but this is the first year when researchers could confirm that it is killing hibernating bats. Soudan is the state’s largest known hibernaculum, home to an estimated 10,000-15,000 bats. If the disease proceeds as it has elsewhere, in excess of 95 percent of those bats will die over the next few years, according to Gerda Nordquist, a bat expert who has been studying the mine’s bat population for years.
Park officials say the situation is disturbing, but it likely will have no significant impact on underground tours at the park. During a conference call on Wednesday, Dr. Jeremy Coleman, who is coordinating the national response to WNS for the U.S. Fish and Wildlife Service, said the WNS infection is spread almost exclusively from bat-to-bat and that chances that the general public could spread the fungus to other caves is quite low. The park did implement a decontamination protocol three years ago, when the fungus was first detected in the mine, and Park Director Jim Essig said those efforts will continue.
“Now that it’s here, we will continue to do everything we can at our parks to prevent human transport of fungal spores to other sites,” said Essig. Although the disease is transmitted primarily from bat to bat, people can inadvertently carry fungal spores to other caves on clothing and caving gear.
Signs of trouble
According to park officials, they began noticing significant numbers of bats emerging from the underground mine in late January, during a cold snap when temperatures were as low as minus 30 degrees. The bats quickly died in the extreme cold and park staff gathered up bodies and sent them a federal lab for testing, which confirmed WNS as the cause.
While WNS isn’t considered fatal by itself, the fungus is believed to irritate bats, causing them to emerge from hibernation at a time when there’s no food available or when conditions are too cold for the bats to survive. Since its first documented case in New York nine years ago, researchers believe WNS has killed more than 5.7 million bats in 27 U.S. states and five Canadian provinces.
The disease is named for the fuzzy white growth of fungus observed on infected bats. Researchers say it is typical for disease symptoms to appear two to three years after discovery of the fungus.
According to Coleman, the infection at Soudan almost certainly came from other bats. He noted that the Atikokan Mine, located about 70 miles north of Soudan in northwestern Ontario, has been infected and that bats from there, or from other infected caves along the northeastern shore of Lake Superior, likely spread the disease to Soudan.
Among the bats most affected by the disease are little brown bats and northern long-eared bats, which make up the bulk of the Soudan Mine’s bat population. Less common tri-colored and big brown bats are also found in the mine and are known to be susceptible as well.
While the initial outbreak of WNS has been devastating elsewhere in eastern North America, researchers say there are a few rays of hope for getting the pandemic under control, including some treatments that have shown promise in lab testing. An ongoing study by University of Minnesota researcher Christine Solomon is testing microbes found in the Soudan Mine to determine if they could slow the growth of the WNS fungus.
There is also growing evidence that bats are figuring out ways to survive the fungus on their own. The fungus thrives under certain conditions, with the right humidity and temperature, and Coleman said it appears that bats are now favoring locations within hibernacula that are less favorable to the fungus.
Bats can recover from the disease if they survive the winter, and biologists are studying why some bats in affected caves are surviving multiple years.
Essig said that was encouraging news, since the Soudan Mine offers a substantial range of temperature and humidity for bats. “There’s a little bit of hope there,” said Essig. “If they can survive the first hit and get to better areas next winter, they might have a chance.”
DNR officials are encouraging anyone who sees a sick or dead bat to submit a Bat Observation Report. DNR staff review these reports and additional follow-up or testing is conducted as needed. To learn more about white-nose syndrome and Minnesota’s bats, visit www.mndnr.gov/wns.