SOUDAN— There’s good news to report on the status of the hibernating bat population in the Soudan Mine. The latest test results collected from bats at the mine all came back negative for the presence of the fungus that’s believed to cause deadly white nose syndrome.
Researchers gathered swabs from a total of 50 bats in the mine this winter. That represents just a thin sliver of the total bat population in the mine, so it’s not a guarantee that the fungus is completely absent. Even so, “it’s positive news,” said Gerda Nordquist, a bat specialist with the Minnesota Department of Natural Resources.
The latest results were consistent with tests done in 2013, which also came back negative. In 2012, however, four of 50 samples taken from two different locations tested positive for the fungus, and that prompted the DNR to take steps to try to address the issue. Two bats from the Soudan Mine and two more from Mystery Cave in southeastern Minnesota each tested positive for the fungus that year. Those samples had initially tested negative, but a better, more accurate test conducted on the samples several months later, came back with the positive readings.
The fungus has all but wiped out the populations of two or three different species of bats in the eastern United States, where the fungal disease was first detected. The appearance of the fungus at two Minnesota locations was the first evidence that the fungus may have spread to the state.
So far, researchers say none of the bats in Minnesota have exhibited symptoms of white nose syndrome itself, but symptoms typically follow the arrival of the fungus, and usually appear within a year or two.
“As we’ve increased our understanding, we are detecting the fungus earlier in the infection,” said Jeremy Coleman, white nose syndrome coordinator for the U.S. Fish and Wildlife Service. “We don’t know for sure when they might exhibit disease.”
The arrival of the fungus has eventually proven deadly to hibernating bats, however, particularly species like the little brown bat and the northern myotis, which tend to hibernate in damp caves, where the fungus seems to thrive. Nordquist said those species of bats make up about 98 percent of the bats that hibernate at the Soudan Mine, so a mass die-off of those species would be devastating, she said.
Once established in a bat colony, or hibernacula, the white nose fungus spreads mostly bat-to-bat. The infected bats exhibit a number of symptoms, including the development of a white fuzz around their noses and mouths. The fungus appears to irritate the bats, causing them to arouse from hibernation too early, expending limited energy reserves, and resulting in death. Within an infected population, mortality can be 90 percent-plus within two to three years, according to Coleman.
While the latest news is positive, Nordquist said researchers still have more to learn about how quickly the fungus can become established in frontier sites, such as Minnesota. The 2012 test results could be a false positive, but Nordquist said the odds of that are quite small. More likely, she said, “it could be an errant bat or two got in there and then left.”
Whatever the case, the 2012 results prompted the DNR to take more aggressive steps to try to head off any additional infection at Soudan, or to prevent the spread of any of the fungus from Soudan to other locations in the state.
The park began using a dry disinfectant mat for visitors as they enter and leave the underground mine. This year, said Park Manager Jim Essig, the park will use a wet and dry disinfectant method that should be more effective at limiting the spread of any fungal cells. While the effectiveness of the disinfecting effort is unclear, Essig said it helps serve as a valuable educational tool as well.
Nordquist said the measures are a good idea even with the latest negative test results.
Meanwhile, Nordquist said researchers are stepping up their efforts to find ways to counteract the impact of the fungus before it spreads more widely. Currently, she said, much of the focus is on biological controls, such as using microbes or even other fungi to either inhibit the growth of the toxic fungus or to outcompete it.
“Right now, there’s testing being done on some things,” said Nordquist, but she said a solution is needed soon to prevent further damage to bat populations in the U.S. Even if the fungus no longer exists in Soudan, Nordquist said it’s probably only a matter of time before it shows up in earnest. “Our bats can’t wait much longer,” she said.