Scientists confirmed white-nose syndrome (WNS) in hibernating bats from the Czech Republic. These findings, reported in the Journal of Wildlife Diseases, are the first documentation that G. destructans can cause disease in bats of Europe.
White fungal growth on the muzzles of hibernating bats in Europe has been observed for almost 3 decades. Over the past few years, samples of the white fungal growth from bats in 12 European countries were identified as G. destructans. Until now, however, it was unknown whether this fungus caused disease in European bats.
White-nose syndrome was first identified in 2007 among a single group of closely spaced hibernacula in New York that included a tourist cave. Since first discovery, the disease has quickly spread across eastern North America, and it is estimated to have killed more than 5.5 million cave-hibernating bats. This pattern of disease spread suggests that G. destructans was recently introduced to North America, and the most likely source is Europe. Many North American hibernation sites have experienced bat population declines ranging from 95 to 100 percent. Unlike in North America, infection of European bats by G. destructans has not been associated with unusual mortality.
Differences in WNS mortality between bats of North America and Europe are not yet understood. Similar questions also surround apparent differences in WNS mortality between different species of hibernating bats of eastern North America. We do, however, know that G. destructans can colonize skin of hibernating bats without causing the skin erosions or ulcers that define the disease.
For an infectious agent, particularly a cold-loving skin fungus such as G. destructans, to cause disease, many conditions must be met, including those involving the hibernating bats, the fungus, and the environment they share. For example, conditions within hibernacula, particularly at the site of hibernation, may influence the growth rate of the fungus and production of infectious fungal spores. Also, hibernating populations of North American bats are significantly larger than those in Europe, and the size of the hibernating clusters of bats may influence the ability of G. destructans to spread. Along these lines, conditions outside of hibernacula such as winter length and severity may influence the ability of bats to withstand infection over the hibernation season. The body size of bats might also affect the sensitivity of bats to this disease. The greater mouse-eared bat that was diagnosed with WNS in Europe has an average body mass of 26 grams during hibernation. The little brown bat that is most frequently diagnosed with WNS in North America weighs only approximately 7 grams.
It is unlikely that bat populations of North America undergoing extreme mortality due to WNS, can rely on a few survivors that might be able to adapt to this disease. Current rates of mortality among North American bats with WNS are unprecedented and seem to be outpacing the rate at which survivors might compensate, recover, reproduce, and persist.
Nothing currently known will end WNS mortality for North American bats. Preventing spread of the disease is the only defense humans can attempt to control, particularly when human behaviors are involved. Research to better understand WNS in bats and the contributions of the fungal characteristics, the environment, and the behavior, physiology and immunology of bats provide the greatest hope for identifying points of intervention to break the disease cycle. Investigating why WNS causes extensive mortality in North American bat populations but not European bat populations may also provide the insight needed to develop strategies to reduce the effects of WNS.
Carol Meteyer is a veterinarian with a specialty in wildlife pathology. She works at the USGS National Wildlife Health Center where she investigates causes of illness and death in wildlife. In addition to diagnosing causes of wildlife mortality, her research interests are white-nose syndrome in bats, highly pathogenic avian influenza, and other viral diseases in waterfowl, and effects of man-made and natural toxins on wildlife.