A new study carried out at the US Geological Survey (USGS) National Wildlife Health Center in Madison, provides the first direct evidence that the appropriately named fungus Geomyces destructans does cause white-nose syndrome (WNS), a deadly disease that is spreading fast and decimating bat populations in North America.

You can read a scientific paper, written by USGS scientists and partners, in the 26 October online issue of the journal Nature.

The scientists exposed healthy little brown bats to G. destructans while they hibernated in captivity and found 100% of them developed WNS. They also showed that G. destructans can spread from individual bat to individual bat.

USGS Associate Director of Ecosystems, Anne Kinsinger, told the media:

“By identifying what causes WNS, this study will greatly enhance the ability of decision makers to develop management strategies to preserve vulnerable bat populations and the ecosystem services that they provide in the US and Canada.”

WNS is causing catastrophic declines in populations of many bat species in North America. The disease is called White Nose Syndrome because it causes a white growth on the skin, including the muzzle, when it infects hibernating bats.

The white growth is the newly discovered fungus Geomyces destructans (literally a destructive species of filamentous fungus), and the authors note in their paper that:

“Colonization of skin by this fungus is associated with characteristic cutaneous lesions that are the only consistent pathological finding related to WNS.”

There has been much debate over whether the fungus causes WNS or is merely associated with it.

Before this study, many scientists believed the fungus causes WNS, but there was also a belief in some quarters that the fungal infection, like many fungal infections in mammals, was caused primarily by immune system deficiency.

Another point also made by those who support the idea that the fungus is an “opportunistic pathogen” linked to but not the cause of WNS, is the fact that it colonizes the skins of bats in Europe, where no unusual numbers of deaths in bat populations have been reported, write the authors.

What has been lacking, is the evidence that G. destructans is the primary cause of the disease.

So, David Blehert, USGS microbiologist and an author of the study, and colleagues, exposed healthy little brown bats (Myotis lucifugus) to pure cultures of G. destructans as they hibernated and found 100% of them developed WNS. They also cultured live G. destructans from the diseased bats, thus “successfully fulfilling established criteria for the determination of G. destructans as a primary pathogen”.

Then they confirmed that WNS can be transmitted from infected bats to non-infected healthy bats through direct contact.

They conclude:

“Our results provide the first direct evidence that G. destructans is the causal agent of WNS and that the recent emergence of WNS in North America may represent translocation of the fungus to a region with a naive population of animals.”

Blehert said:

“While our study confirmed that G. destructans is spread bat-to-bat, it is also important to note that virtually all pathogens, especially spore-producing fungi, are spread by multiple routes.”

“This is the reason that in an effort to further control the spread of WNS, resource management agencies have implemented universal precautions, including limiting human access to sensitive environments occupied by bats, decontaminating equipment and clothing moved between these environments, and restricting the movement of equipment between sites,” he added.

Estimates suggest that insect-eating bats save the US agricultural industry alone billions of dollars each year in insect pest-control expenses.

But bat populations have been falling at an alarming rate since 2006, when WNS first appeared in New York States. Some estimates put the overall decline at over 80% in the Northeast US, the most severely affected part of the country.

G. destructans has also spread southward and westward and is now present in 16 states and 4 Canadian provinces.

Written by Catharine Paddock PhD