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Bat-Killing Fungus Continues Deadly Spread; Death Toll Now at 7 Million

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little brown bat white-nose syndromeThings keep getting worse for North American bats. Nearly seven million from various species have now fallen victim to the deadly but little-understood disease known as white-nose syndrome (WNS) since it was first observed in February 2006. The fungus that causes WNS, Geomyces destructans, has quickly spread from cave to cave and state to state, and the disease itself was confirmed for the first time west of the Mississippi River this week. This makes 19 U.S. states and four Canadian provinces where the disease can now be found. WNS has a 70 to 100 percent mortality rate; it has no cure or treatment, nor is it entirely clear how it kills bats.

The Missouri Department of Conservation (MDC) confirmed April 2 that WNS had been found on three bats in two caves, exactly two years after the fungus was first observed there. “White-nose syndrome in Missouri is following the deadly pattern it has exhibited elsewhere,” Mollie Matteson, a bat specialist with the Center for Biological Diversity (CBD), said in a prepared statement. “First the fungus shows up on a few healthy bats. A couple of years later, the disease strikes. And if the pattern continues, we can expect that in another few years, the majority of Missouri’s hibernating bats will be dead.”

The names and locations of the Missouri caves, which are closed to the public, were not disclosed in order to limit the chance of humans accidentally stressing the remaining bats. “Disturbing bats in caves while they roost or hibernate can increase their stress and further weaken their health,” MDC bat biologist Tony Elliott said in a prepared statement.

WNS has, in just the past few weeks, been confirmed in Delaware, Alabama, Maine’s Acadia National Park, and Great Smoky Mountains National Park in Tennessee and North Carolina. The disease has also spread to new locations in Kentucky, Ohio and Indiana. The fungus appears to be transmitted from bat to bat, or by humans visiting bat caves. The disease threatens four endangered species: Indiana bats (Myotis sodalis), which have been killed by WNS: gray bats (Myotis grisescens), on which the fungus has been found; and the Virginia big-eared bat (Corynorhinus townsendii virginianus) and the Ozark big-eared bat (Plecotus townsendii ingens), both of which live in areas affected by the fungus.

As the WNS name suggests, the fungus first manifests as white fuzz on the faces of infected hibernating bats, but according to the U.S. Geological Survey’s Fort Collins Science Center, the real damage may come when it spreads to bats’ wings: “Wing membranes represent about 85 percent of a bat’s total surface area and play a critical role in balancing complex physiological processes. Healthy wing membranes are vital to bats, as they help regulate body temperature, blood pressure, water balance and gas exchange—not to mention the ability to fly and to feed.” According to the U.S. Fish and Wildlife Service (FWS), bats with WNS behave uncharacteristically, such as flying outdoors during the cold winter months or gathering at cave mouths when they should be hibernating. Such behavior could cause bats to burn off their winter fat reserves, leaving them susceptible to freezing or starvation.

Although WNS and the Geomyces destructans fungus appear to have no effect on humans, their potential impact on human health is troubling. As the bats disappear, growing insect populations could spread disease or devastate agricultural crops. Citing just the most recently afflicted state as an example, Missouri’s 775,000 gray bats eat more than 223 billion bugs each year, according to the CBD. Although the potential effect on U.S. agriculture has not yet been felt, a recent study found that the loss of North American bats could lead to agricultural losses of more than $3.7 billion per year.

Research into WNS is ongoing, and there are a few small rays of hope. Some European bat populations that have come in contact with the G. destructans fungus appear to be resistant to it, and in fact some scientists theorize the fungus may have originated in Europe and recently been carried to the New World by humans. In addition, a few small populations of little brown bats (Myotis lucifugus) in Pennsylvania and Vermont also appear to have remained healthy despite three years of contact with the fungus, for as-yet-unknown reasons.

For more information on WNS, visit the FWS resource page about white-nose syndrome, including their safety guide for cavers, or follow FWS’s White-Nose Syndrome in Bats page on Facebook. The CBD’s Save Our Bats campaign offers several actions people can take to encourage government efforts to help slow the spread of the disease.

Photos: White-nose syndrome on a little brown bat (Myotis lucifugus) taken March 30, 2012, in Missouri, courtesy of Missouri Department of Conservation. Map of white-nose syndrome by county/district as of March 30, 2012. Courtesy of Cal Butchkoski, Pennsylvania Game Commission, via the U.S. Fish and Wildlife Service

Correction April 4: The list of affected endangered bat species has been updated.

John R. Platt About the Author: Twice a week, John Platt shines a light on endangered species from all over the globe, exploring not just why they are dying out but also what's being done to rescue them from oblivion. Follow on Twitter @johnrplatt.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. CharlieinNeedham 3:43 pm 04/4/2012

    In human medicine, fungal diseases are commonly seen in those taking antibiotics, but are rare otherwise in those who are not immunocompromised. (For example “yeast infections” are are often seen in women on antibiotics. They carry candida as ever present, but only develop candida infections when the antibiotcs suppress their normal bacterial flora.)

    Could there be an analogous situation in bats, where the normal bacteria nasal flora is decreased, leading to the easy overgrowth of the causative fungus, Geomyces destructans?

    (Clearly, Geomyces destructans is not a very agressive organism. Bats don’t get the fungus and have a rapid downhill progression and die within days.)

    So my questions are:

    1. Has anyone checked to see if the nasal bacterial levels in bats in endemic areas is lower than in other areas?

    2. Could the level of nasal bacteria have been lower in this region for a relatively long time, without consequence, until Geomyces destructans arrived as a fungus with just enough invasiveness to become a deadly pathogen?

    3. Although pesticides are not “antibiotics”, could they
    chemically kill the normal nasal flora of bats, setting up for overgrowth of Geomyces destructans?

    Link to this
  2. 2. CharlieinNeedham 11:33 am 04/5/2012

    Had a few more questions:

    4. Is the nasal flora in the pockets of resistance in Vermont and Pensylvania, or those resistant populations in Europe, different in either types of bacteria present, or numbers of bacteria?

    5. Would it be possible to replace nasal flora in endemic regions with nasal flora types from resistant area bat populations, similar to the way the probiotic lactobacillus from yogurt can repopulate the GI tract in people with gastrointestinal problems?

    Link to this
  3. 3. bucketofsquid 4:43 pm 04/5/2012

    Won’t the amount of agricultural loss depend on just which bugs the bats eat? Do bats eat bees? I know they eat mosquitoes so disease spread will increase.

    Link to this
  4. 4. Ed Greding 1:27 am 04/8/2012

    What kind of fungus is involved? Is it the same or related (by genus or family) to the Chrysitid fungus that is decimationg frogs over much of their ranges?

    Do bats eat mosquitoes?

    Link to this
  5. 5. CharlieinNeedham 8:50 pm 04/8/2012

    Bucketotswquid: Bats don’t eat bees. They do eat lots of mosquitos, so mosquito populations likely will increase.

    Link to this
  6. 6. CharlieinNeedham 9:02 pm 04/8/2012

    Ed Greding: The fungus involved is Geomyces destructans.
    This is not related to the fungus that is decimating frogs.
    Bats would seem to be at high risk for fungal disease as their body temperatures and overall body functions are greatly decreased while they hibernate in the winter. This also includes a decrease in their immune function.
    But no fungus until very recently has affected American bats like this.
    Indeed, even Geomyces destructans does not seem to be inherently very invasive.
    As evidence of this, Geomyces destructans has been found in European bats for a long time, but without ill effect. White-Nose Syndrome Fungus (Geomyces destructans) in Bats, Europe
    And another puzzle is that pockets of resistance have been found in Vermont and Pennsylvania. Little brown bats found that appear to resist disease that has devastated species

    Link to this
  7. 7. Amcurious 4:39 pm 09/27/2012

    Could there be a connection between the white nose fungus of bats and the white fungus of cutter ants?

    Link to this
  8. 8. John R. Platt in reply to John R. Platt 8:37 am 09/28/2012

    Not that I’ve heard of yet.

    Link to this

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