Fungal pathogen that causes disease in bats found in four new counties

Press release from N.C. Wildlife Resources Commission:

The news continues to be bad for bats in the Tar Heel state.

After receiving results from winter bat surveys recently, biologists with the N.C. Wildlife Resources Commission and N.C. State Parks have confirmed the presence of Pseudogymnoascus destructans (Pd), the fungal pathogen that causes white-nose syndrome (WNS), in four new counties in North Carolina.

WNS is a deadly disease that has killed millions of bats in the eastern United States — and thousands of bats in North Carolina — since it was first detected in New York 13 years ago.

Even more discouraging is the eastward trajectory the fungus appears to be taking — spreading to more Piedmont counties. Up until 2015, WNS had been found only in hibernating bats in mountain counties, presumably because the fungus that causes WNS can survive only in the cold temperatures found in mines and caves (hibernacula), most of which occur in the mountains.

However, during surveys conducted in January and February, biologists detected the first evidence of Pd in Madison, Montgomery, Rowan and Gaston counties. This finding brings the number of North Carolina counties with confirmed presence of Pd to 16.

Bats at the Madison County site were the only ones that showed visible signs of the fungal growth consistent with WNS, which is the telltale sign of WNS infection. At the other three sites, bats tested positive for Pd, although they did not show the characteristic white fungus that gives the disease its name.

“While it wasn’t surprising to see WNS show up in Madison County given its close proximity to four other WNS-positive counties, it was disappointing to see Pd-positive results in Montgomery, Rowan and Gaston counties,” said Katherine Etchison, the Commission’s bat biologist. “These counties indicate a definite trend of the fungus moving eastward.

“We started seeing this trend when a site in Stanly County showed a positive result for Pd in 2015; however, this site has not tested positive since then and bats have never appeared infected so there was some ambiguity regarding the presence of Pd in this area.”

The next Piedmont site to test positive was over 70 miles to the north in Stokes County in 2017, which also tested positive this year.

“The new Piedmont sites where Pd was detected this year are much closer to Stanly County—the Rowan County site is just 17 miles away and the Montgomery County site is only 9 miles away,” said Etchison. “While the Gaston County site is about 65 miles from the Stanly County site where Pd was first detected, it borders a county in South Carolina where Pd was detected in winter 2017-18.”

These results make sense given that the new Piedmont sites are in areas with many inactive gold mines that harbor hibernating tri-colored bats. These bats likely spread the fungus from site to site when visiting numerous hibernacula in the fall for mating.

While the survey results were disappointing, Etchison is somewhat encouraged by the fact that biologists saw no signs of fungal growth at any Piedmont or Coastal Plain site, even the ones that tested positive for Pd.

“The fungus is the first step in the WNS equation, but other factors like cold temperatures, high humidity levels, and long-duration hibernation are needed to result in a WNS infection,” Etchison said. “The fact we did not see fungal growth, which is the typical giveaway of a WNS infection, could mean that other factors that contribute to WNS infection are not ideal. The Piedmont winters are shorter and warmer than in the Mountains where WNS has been devastating and Piedmont bats are able to arouse and feed on warm winter nights when insects are active.”

Mortality from the disease usually occurs when bats repeatedly expend energy to clean the fungus off themselves during winter in areas of no insect availability and they eventually starve to death. If Piedmont bats can feed during winter and replenish fat stores, or if hibernacula are too warm or dry, bats could avoid a WNS infection even if Pd is present at the site.

“The Stanly County site gives me hope that this is the case in the Piedmont, but only time and continued WNS surveillance will tell,” Etchison added.

Despite the presence of Pd in these new counties, winter bat counts in the Piedmont remain stable, although they are low — from one bat found at one site to 30 bats found at another site. Though these counts are just a fraction of what Mountain hibernacula formerly held, the 30-bat site is currently the highest count of hibernating tri-colored bats in any known hibernaculum in the state.  Most sites biologists have surveyed in the mountains have had over 90 percent declines in bat populations since WNS was first discovered. Some declines have been as high as 99 percent.

While WNS has a deadly effect on bats, it does not affect people — at least not directly. Indirectly, however, it can have a huge impact on humans by reducing the number of bats in North American ecosystems. The U.S. Geological Service estimates that loss of bats in North America could lead to agricultural losses exceeding $3.7 billion annually.

“Bats in these ecosystems are insectivorous and may consume their body weight in insects in a single night,” Etchison said. “Many insects eaten by bats are crop and forest pests.”

Biologists will continue their long-term monitoring efforts of bats in North Carolina, concentrating their efforts on caves and mines in the Piedmont and Coastal Plain. But first they need to find hibernacula to survey— a task that is easier said than done, according to Etchison.

“If landowners have a cave or mine on their property that they’d allow us to survey, that’d be great,” Etchison said. “They can contact me at katherine.caldwell@ncwildlife.org for more information.”

How You Can Help

While WNS is transmitted primarily from bat to bat, it can be spread to new sites by humans who inadvertently carry fungal spores from cave to cave on their shoes, clothing and caving gear. The Commission encourages people to help bats by staying out of caves and mines. Linville Caverns, the only commercial cave in western North Carolina, is helping to reduce the spread of WNS by asking visitors to disinfect footwear after visiting the cave by briefly stepping onto a special decontamination mat outside the cave.