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Description and Distribution
White-nose syndrome (WNS) was first documented in bats in New York in winter 2006-2007. The syndrome was named for the white fungus that sometimes develops on the muzzle of the bat, giving the appearance of a white nose.
The fungus has been identified as a new species named Pseudogymnoascus destructans. Places where bats hibernate, such as caves or underground mines (known as 'hibernacula'), are ideal environments for this fungus, as it thrives in cold, damp conditions. It is unclear if the fungus is the cause of disease or an abnormal growth of a naturally occurring fungus resulting from infection with some other pathogen. Not all bats affected by the disease have white muzzles and the fungus often grows on the naked wing and tail membrane as well.
WNS primarily affects bats during hibernation. Infected bats prematurely awaken from hibernation, rapidly deplete their fat reserves, and are unable to survive the winter. Bats with WNS often exhibit unusual behavior such as flying during daylight hours or gathering outside of caves in cold weather.
To date over 5 million bats have died from WNS. Some bat colonies in the northeast US have experienced die-offs in excess of 90%. Entire populations and endangered species of bats are at risk. Scientists across the country are working vigorously to understand more about this disease.
Transmission and Development
Transmission of the fungus associated with WNS is believed to occur in one of two ways: 1) through bat-to-bat contact or 2) by humans visiting caves and mines. Bat-to-bat contact occurs during pre-hibernation movements, while in hibernacula and in maternal colonies. Conditions in hibernacula make it an ideal place for the spread of the fungus as temperature and humidity are optimal and high densities of bats are gathered in one location.
There is also evidence that the fungus is inadvertently spread by humans. Cavers (spelunkers) may transfer the causative agent on their clothing, shoes and gear between caves. Evidence of WNS has been documented in caves absent of bats and many states have restricted access to caves to prevent further spread by humans.
Clinical Signs and Pathology
The disease is called white-nose syndrome (WNS) because it causes white fungal growth on the muzzles and wings of infected bats. WNS infects bats when they are hibernating causing damage to the wings, tail, and ears, which affects their water balance. The bats then wake up more often during hibernation using fat reserves and consequently resulting in starvation before the spring. Also, infected bats have been observed to groom more around their nostrils and this increased grooming behavior also uses energy and causes the bats to loose fat reserves. WNS may result in 90 to 100 percent mortality in bats, however, this is dependent upon the location and species of bat.
WNS affects bats while in hibernacula. Many insect-eating bats survive winter by going into hibernation, during which their body temperatures are lowered and fat deposits collected during summer months are utilized. WNS is believed to disrupt this cycle, causing bats to prematurely and repeatedly awaken from hibernation, quickly depleting their fat reserves and losing body condition. Bats weakened by the loss of fat reserves are unable to replenish them due to lack of food (insects) in winter and die before spring.
Bats affected by WNS have been observed exhibiting unusual behaviors, such as moving into cold parts of the hibernacula, or flying outside during cold weather or daylight hours.
Many bats with WNS have a white fungus on their muzzle, wings and other naked parts of their body. Lesions and scarring have been observed on the wings, tails and faces of bats that have been exposed to the fungus. Although the fungus itself is typically only visible in bats hibernating during winter, the wing damage caused by the fungus may be visible year round, and contribute to bat deaths even in summer.
Various diagnostic methods are being employed to identify WNS including visual identification of the white fungus or lesions consistent with an overwinter infection; fungal culture; histopathological examination; and polymerase chain reaction (PCR). USGS National Wildlife Health Center in Madison, WI is the primary reference laboratory for diagnosis of WNS.
Treatment and Control
At this time, there is no definitive treatment for white-nose syndrome. However, researchers are actively searching for treatment options for this devastating disease affecting millions of bats across the nation.
White-nose syndrome (WNS) has spread across the nation as a consequence of a few different methods. The fungus can be spread from bat-to-bat via physical contact, potentially as a result of allogrooming. In addition, bats can become infected if the fungus is present on the surfaces of the mines or caves. Furthermore, humans can introduce the fungus into new locations by accidentally carrying the fungus on their shoes, gear, or clothing. Therefore, if you will be visiting a potentially infected cave or mine, you can help prevent WNS by decontaminating your gear.