A Deadly Disease
A Deadly Disease
White-nose Syndrome (WNS) is a fungal disease that has killed millions of bats in North America since it was first discovered in a single cave in New York in 2007. The fungus grows on the skin tissues of hibernating bats, repeatedly rousing them from hibernation and causing them to consume their winter fat stores and starve to death before spring.
The disease is causing massive population declines for multiple hibernating bat species – resulting in the most precipitous wildlife collapse of the past century. The disease has hit northern long-eared bats particularly hard – threatening this species with extinction. Northern long-eared bats disappear from their winter homes within just a few years of the fungus showing up. Species that were once common like the little brown bat and tricolored bat have been decimated. Sites that used to have thousands of bats dwindle to just a few individuals struggling to hang on.
Today, bats with the disease symptoms of WNS are found in 30 US states and 5 Canadian provinces. In addition, the fungus that causes WNS has been found in three more US states at the frontier of its spread across North America. WNS continues to spread from its epicenter in New York across North America. In March 2016, a little brown bat (Myotis lucifugus alascensis) found sick in King County, Washington, tested positive for WNS. Genetic analysis of the fungus from this bat found that the strain of fungus was genetically similar to strains found in the eastern U.S., indicating that the fungus made a 1,300-mile leap from its previous westernmost detection.
In surveys conducted in January and February 2017, the fungus was detected on three species of hibernating bats in six counties in Texas by biologists from Bat Conservation International and Texas A&M University. The fungus was detected on three tri-colored bats, seven cave myotis and one Townsend’s big-eared bat. This was first detection of the fungus on cave myotis and Townsend’s big-eared bats. While the presence of the fungus has been confirmed, signs of the disease in Texas have not yet appeared. Early detection methods of taking a skin swab from bats allows researchers to detect the fungus as soon as it arrives and before bats get sick.
WHAT WE ARE DOING
The Cause of White-nose Syndrome
This disease was named “White-nose Syndrome” because of the telltale white fuzzy growth on the nose, ears, and wings of infected bats. Scientists identified a previously unknown species of cold-loving fungus, Pseudogymnoascus destructans (previously Geomyces destructans), as the cause of the skin infection. P. destructans thrives in low temperatures (40–55° F) and high humidity – conditions commonly found in sites where bats hibernate.
Infection of P. destructans can causes skin lesions and disrupt the natural physiological processes and torpor cycles during hibernation causing bats to die. Not all species are impacted the same way and some seem more susceptible to mortality from the disease than others. Scientists are working to determine the conditions that increase a bat’s susceptibility to WNS and disease mortality.
Where did the fungus come from?
WNS was first documented at four sites in eastern New York 2007. After that, photographs taken in February 2006 were found, showing affected bats at another site.
The disease is caused by a fungus from Eurasia, which was accidentally transported here by humans. In Europe, 13 bat species have been confirmed with WNS or the fungus, but there has been no mass mortality associated with these observations.
BCI has been working with European researchers to locate the potential source of the strain of the fungus that got introduced to North America. To date, our partners have sampled over 425 sites from across Europe in the search for the potential area where the fungus originated from.
Pd in Europe
A study funded by Bat Conservation International investigated Pd’s origins on a molecular level. This allowed the researchers to evaluate the genetic similarity of European and American Pd and assess whether Europe was a likely source for the recent introduction of the pathogen to North America. It found a higher diversity of Pd within the European population of bats versus North America, demonstrating a long-term presence in Europe, and strongly supporting the introduction of the fungus to the eastern region of the USA from Europe.
Given there is no bat migration occuring between North America and Europe, it is very likely that the fungus has been introduced to North America via anthropogenic activities. The introduction of new pathogens into native populations represents the undesired consequence of global movement of humans, animals and trade.
Pd in China
In 2015, bats in northeast China were also found to be infected with Pd. A team of American and Chinese researchers found the fungus in caves where bats hibernate and found bats infected with the fungus. Although infected bats had lesions characteristic of the disease and similar to lesions seen in North American bats, the researchers do not know the extent to which Chinese bat species are affected by the disease. Although historic population counts for bats in China do not exist, there has been no obvious evidence of the kind of population collapses that have been seen in North America and the disease has likely been there for a very long time as in Europe.
Bat species in areas where the fungus has existed for a long time may have evolved resistance to or tolerance of the disease, but may still suffer mortality. The overlapping ranges of the affected bat species in Europe and Asia suggest that the fungus may be widely distributed across all of northern Europe and Asia.
How WNS is Spread
Bat-to-Bat: The fungus that causes WNS is believed to be transmitted primarily from bat to bat and bat to cave.
Substrate-to-Bat: P. destructans can survive in sediments and on the walls of caves and mines where bats hibernate. Healthy bats entering previously infected sites likely get exposed to the fungus from the hibernaculum environment.
Other Means: Scientists have demonstrated that it may be possible for humans to inadvertently carry P. destructans spores on their clothing or equipment.
Signs of the disease
Bats affected with WNS do not always have obvious fungal growth. Sometimes bats with WNS simply display unusual behavior such as flying outside during the day in near-freezing weather. This quickly uses up their fat reserves at a time when insects are not available for food. As a result, in winter you may see dead or dying bats on the ground or in buildings or other structures. If you encounter a bat, do not handle it!
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