The speed at which this problem has spread and the degree of impact on the bat numbers is, well it's really beyond what anyone would have imagined. I don't think that it's an exaggeration to say, even in the field of wildlife study, there are few examples of disease issues that have been so virulent & complete in their impact. -Carl Herzog, NYSDEC
|
Unless you've been living in a cave these last few years you will have heard about the killer fungus that causes White Nose Syndrome and it's deadly march across the Eastern United States. But wait, if you'd been living in a cave, you might well be dead. Pseudogymnoascus destructans, the fungus that causes White Nose Syndrome (WNS) is possibly the most deadly disease to hit wildlife in the United States and is causing one of the most precipitous wildlife declines in recorded history. WNS has killed millions of bats and every year pushes westwards leaving thousands more dead in its wake.
|
For the last few years, biologists have watched thousands of bats fly into their caves and mines for hibernation, knowing that tens of thousands probably won't fly back out. "The worry is great, tremendous," says Greg Turner, a Pennsylvania researcher specializing in endangered mammals. By late winter the reports start coming in of the latest areas with confirmed WNS cases. It's a horrible feeling waiting and every few days hearing of yet another colony of bats that has disappeared or another state that has been infected. In 2011, cases of the mysterious disease were confirmed for the first time in Ohio, Indiana, North Carolina and Kentucky and in the Canadian provinces of New Brunswick and in Nova Scotia. So far, a total of 18 states, mostly in the eastern U.S., and four Canadian Provinces have been confirmed as infected.
What is WNS? How does WNS relate to Geomyces destructans? Why bats? “White nose syndrome” describes the white fuzz that develops on the ears, nose and/or wings of hibernating bats infected by P. destructans. The fungus has also been known to completely cover the animal, attaching the victim to the cave's surface. |
|
Why does WNS result in such a severe mortality rate?
1. As outlined above, whether the bats wake up during torpor because of hunger or thirst, constant arousal during the winter months when there are limited resources is a death sentence. 2. P. destructans also destroys hair follicles, and sebaceous and apocrine glands. This disrupts protective secretions that moisturize and water-proof skin, and may provide a protective barrier against harmful microorganisms. Additionally, the secretions may supply nutrients to symbiotic, and possibly protective, microorganisms. |
Can bats survive WNS?
Despite exhaustive efforts by American wildlife rehabilitators and veterinarians, most bats who contract WNS do not recover (see box, “What are Wildlife Rehabilitators doing about WNS?”). Even when the wings don't look too bad to the naked eye, a look under the microscope often reveals deadly damage already starting to take hold. This suggests that bats may be suffering more than we currently appreciate. If a bat does survive WNS, will it be OK? It is possible that injured wings, even if healed, may result in decreased flight ability and efficiency. Compromised wing structure and muscles may make wings unstable and harder to control in flight. Damaged sensory nerves may diminish the ability to sense airflow across the wing's surfaces, resulting in a decreased ability to control flight; and with compromised flight, the bat is more vulnerable and less able to survive in its environment. |
This may be particularly true in the Northern Regions of the US, where agriculture is a multi-billion dollar industry, accounting for about 20% of all jobs across North Dakota, Montana and Idaho, and cold winters make it a perfect place for the fungus to take hold. In these areas, the estimated annual value of bats is nearly $2.7 billion (nearly one-third of the market value of crops sold in these states). For these economic reasons, the USDA Forest Service is considering closing caves in North Dakota, Montana, north Idaho, and northwest South Dakota. As one regional forester comments, “I don't believe we can approach this issue with a wait-and-see attitude, once one cave in the region is affected, the likelihood increases for a more rapid spread among the bat population” (Leslie Weldon, U.S. Forest Service).
|
2. It appears that WNS is primarily transmitted from bat to bat, but fungal spores may be inadvertently carried to caves by humans on clothing and caving gear. It is unclear whether bats are still infective during the summer or if it is possible that the disease will spread to tree bats. If transmissible during the summer months, it is very possible that maternity roosts, where large numbers of bats gather during the warmer months, are a primary target for WNS infection. This might also account for the spread of the disease as bats who spend the summer in one state, but winter in another, can carry the fungus to their winter hibernacula initiating the spread of WNS in a previously unaffected area.
|
Mitigating diseases in free-ranging wildlife populations requires very different approaches from those applied in agriculture for domestic animals. Once established, diseases in free-ranging wildlife are rarely, if ever, eradicated. Biologists trying to manage WNS within bat populations face multiple challenges, including the need to deal with numerous host species, long-distance migrations of infected hosts, poor access to some host populations, impracticalities associated with treating individual wild animals, infected hosts that are sensitive to being disturbed and that inhabit fragile ecosystems, and environmental persistence of the pathogen. (Blerhart et al., 2011, Microbe Magazine)
|
We cannot yet rapidly screen sites for the presence of WNS fungus when visibly infected bats are absent, we cannot safely and effectively treat wild bats for WNS, we cannot decontaminate fragile cave ecosystems upon which bats rely, nor can we limit the natural movements of bats. Modifying human activity by implementing decontamination procedures, equipment restrictions, and site closures are the options currently available for managing the spread of WNS; these procedures will be reviewed as indicated by additional scientific findings. (Jonathan Sleeman, USGS National Wildlife Health Center)
|
7. In Tennessee, the Nature Conservancy, Bat Conservation International and the University of Tennessee Knoxville are building an artificial cave free from fungus in an effort to entice bats from nearby colonies to switch homes. If successful it is possible that artificial caves could be located in areas with badly infected natural caves. The infected caves could be closed until researchers learn more about managing the fungus, and in the meantime the bats would have a healthy place to live (see picture to the right).
|
The Nature Conservancy in Tennessee’s proposed artificial bat cave.
|
In conclusion
I hope that this article makes you appreciate that we need to care about bats! As WNS spreads, scientists fear for the enormous hibernation caves in Kentucky and Tennessee where a million or more bats may hibernate in a single cave. Already, states to the west and south of the epidemic are putting precautions into place. In Wisconsin the Big Brown Bat, Little Brown Bat, Eastern Pipistrelle, and Northern Long Eared bat will be added to the state's threatened species list this year in order to provide protection to the bats in the face of the imminent threat of white-nose syndrome. Bats face one of the most significant disease threats to wildlife in history and as scientists race to solve WNS's deadly riddle, let's support our unsung bat heroes! Bibliography |
Our Most Recent Bat Patient: This Eastern Small Footed Bat arrived at Wild Things in October 2011. She was found on the ground in the middle of a city, moved to a nearby tree, and was still there after 36 hours. Something was wrong. She came to Wild Things and appeared healthy. Once warmed and fed, she flew beautifully and has been given a large enclosure to allow her to stretch her wings and fly. However, this little bat belongs to one of the species most effected by White Nose Syndrome; with cold weather approaching fast and not knowing whether her hibernacula may have been disturbed or whether she had had trouble during a migratory flight, it was decided that she would overwinter at Wild Things and be released close to where she was found in the early spring of 2012. Thank you to the kind people who looked after her and made sure she ended up in a safe place with lots of delicious mealworms!
|
|