Since 2006, a deadly epidemic has been raging in North America, causing an environmental catastrophe that remains unknown to most people. White Nose Syndrome, a fungal disease introduced to the US from Eurasia, has infected bat colonies in 29 states, killing up to 90% of infected animals and posing a serious threat of extinction for many species.
White Nose Syndrome photo by USFWS
Most people have never seen a live bat, since they are nocturnal animals and don’t come out during the day. But bats are an important part of the ecosystem: about 20% of all mammal species are bats, and they are one of the most important predators upon insects. Typically, bats hunt at night, using their “sonar” echolocation systems to hunt flying insects, and then roost during the day in shelters like tree trunks, caves or abandoned mines. During the winter when food is scarce, many bat species become torpid and enter a state of hibernation, conserving their energy and living on fat reserves until the spring.
In 2007, wildlife authorities began to notice a decline in the population of Little Brown Myotis Bats, one of the most common species in North America, in New York. Dead and dying bats began to appear with an odd white fuzz around their snouts, which was referred to as “White Nose Syndrome (WNS)”. Researchers at the Federal Fish and Wildlife Service identified it as a fungus, Pseudogymnoascus destructans, which is native to China and Europe. This species is unusual in that it prefers cool temperatures in the 40’s and 50’s, and will not grow in temps above 68 degrees. With their constant underground temperatures around 55, cave systems are perfect habitat for the spores to thrive.
In its native areas, the fungus does not appear to be harmful to the bats. But in North America, the bats did not have any resistance to it, and the fungal spores invaded the skin on the wings and around the nose, eating away at the flesh and causing dehydration. The spores were spread by direct contact, either with other infected bats or with patches of fungus growing on the cave walls. During the winter, when the bats should have been torpid, the infection caused them to wake and, in desperation, fly off in search of food and water. This extra energy prematurely uses up their winter fat reserves, and the bats waste away and starve. Some colonies were wiped out completely, others suffered death rates of over 90%.
Since there are no bat species which normally migrate between the Old and New World, it is suspected that the fungus was introduced to the US by human travelers, perhaps from China. The earliest known occurrence is a photo taken in February 2006 by a cave explorer in Schoharie County NY, showing a patch of P destructans growing on the cave wall. It was probably carried in by another spelunker on his shoes or equipment. (Research has shown that the spores can survive for several years on clothing.)
Since then, the fungus has spread quickly. Within a year of its discovery it was found in caves throughout New England; by 2009 it had reached Canada and Virginia, and by 2011 it had spread as far as Arkansas. As of 2016 the WNS fungus has been found in 29 states and 5 Canadian provinces. Most of the West is currently unaffected, although a single infected bat was found in Washington, near Seattle, in 2016, and another bat from the same area was found to be carrying the spores.
So far, it seems as though only those bat species which hibernate in mass congregations are vulnerable to the disease; other species which hibernate individually or migrate for the winter seem unaffected. Bats which live on flower nectar also seem unaffected. Of North America’s 45 bat species, seven have been found with WNS, and five more have been found to be carrying the fungal spores but were not exhibiting any symptoms of the disease. Three of the affected species were already suffering from habitat loss and listed as endangered species–the disease is now threatening to wipe them out completely. Other bats have been reduced by as much as 80%. The Little Brown Myotis, once abundant throughout the northeast, is now being considered for listing as a “threatened species”. Bats are particularly vulnerable to population decreases because they have a low rate of reproduction.
Desperate efforts are being made to halt the spread of the disease. Working in cooperation with caving associations, the USFWS has issued a set of guidelines to protect the bats. A large number of caves and abandoned mines have now been closed entirely to the public. In tourist caves, such as Carlsbad Caverns and Mammoth Cave, visitors are asked if they have visited any other caves recently. Anyone who has been inside a cave that is known to be infected is required to disinfect their clothing or equipment by soaking it in 150-degree water, which kills the spores.
There is also a research program underway to find a possible biological control for the fungus, and several strains of bacteria from China have been identified which attacks P destructans. Before these can be released, however, they must undergo testing to confirm that they are themselves not potential threats to any native species, and that will take several years.