April 1, 2010

Caves, bats, and a newly emerging disease

I've explored caves for practically my entire life. At least a couple times a month for over 25 years, I've ventured into the dark world beneath the earth's surface to explore a world that most people will never see. The reasons I like to explore caves are as complex as the caves I visit. I love the effort required to hike to and locate small cave entrances tucked away on the side of a hill. I enjoy the technical aspects of climbing up tight canyons, crawling through low puddles of mud, and using ropes and harnesses to rappel down to areas otherwise inaccessible. I love finding delicate formations and emerald green pools hidden among cathedrals of solid rock. I have also always loved seeing the strange animals that live in one of the world's most unusual (and totally dark!) environments. My favorite underground animal to observe has long been the bat.

Now, bats across the eastern US are in serious trouble, and over the past two years my love of caving and my love of bats have collided as I've watched in horror as a new, fatal disease has swept through the bat population. In 2006, a cave explorer in New York noticed a few bats with an odd white fungus on their noses, as well as several dead bats on the cave floor. He took some pictures. The next winter, New York biologists found disturbing signs that something was seriously wrong with the bat colonies. Bat were found roosting unusually close to cave entrances, bats were seen flying around outside in the dead of winter when they should have been hibernating, and many of the bats had the strange white fungus on their noses. By the spring of 2007, thousands of dead bats were found in New York caves, and bats that were still alive had white noses. What was going on?

As researchers continued to monitor caves in the northeast, they found more and more caves with white-nosed bats. So far, over a million bats have died, and there are no signs that the syndome is getting better or going away. Unfortunately, each winter, the fungus spread to more caves farther away from the epicenter in New York. Each winter got worse. Mortality rates are often 100% in affected caves. Some reports say that the northeast now has almost no bats left. Last winter, WNS spread from the northeast to the Virginias. This winter, it spread to Tennessee. The last reported case of WNS in Dunbar Cave, TN is 100 miles from my house. Only 150 miles from Dunbar, in northeast Alabama, is the largest gray bat hibernaculum in the country. Researchers names this affliction White Nose Syndome, or WNS.

To understand why this syndrome is spreading throughout the country, it might help to understand a bit about bat ecology and migration. Several different species of bats are currently affected by this syndrome, and they all have different habitats as far as where they live during the summer and winter. Many bats live in the forest during the warm summer months or in warmer caves where they can give birth and raise their young. In the winter, most bats migrate at least a short distance to cold caves that are ideal for dropping their body temperature to near freezing, allowing them to enter a torpor for winter hibernation. As a result, bats fly all over wide ranges, come into contact with other species of bats, and probably encounter a variety of habitats during the year.

So what do we know so far about WNS? Researchers succeeded in identifying the fungus, appropriately naming it Geomyces destructans. The researchers found that WNS is "characterized by the presence of profuse yet delicate hyphae and conidia on bat muzzles, wing membranes, and/or pinnae, although these surface signs are readily removed. Histological examination of infected bats shows that fungal hyphae pervade the bat tissue filling hair follicles and sebaceous glands, yet the fungus does not typically lead to inflammation or immune response in the tissue of hibernating bats (Meteyer et al. 2009)." The species thrives in cold conditions. Gene sequencing showed that the fungus is in the genus Geomyces, but the asymmetrically curved conidia are unlike any described species. Interestingly, the new, deadly fungus is closely related to Geomyces pannorum, which causes skin infections in humans. The fungus is new to science.

Even though researchers were able to identify and name the new fungus, there are many more questions than answers. Bats seem to be affected only during hibernation when they roost in cold locations and their bodies go into torpor. It's currently unknown if the fungus itself is what's killing the bats or if the fungus is just a symptom of an underlying and yet unidentified condition (although some researchers now say they believe the fungus is to blame). Affected bats are emaciated and seem to arouse during hibernation to look for food, but we don't know if bats enter hibernation in an emaciated state or become emaciated during the winter. Nobody knows if there is any way to help bats fight off this fungus, remove the fungus from the environment, or generally help stop the bat deaths. Many studies are looking at these kinds of questions, but the real question is will answer arrive in time? Research has shown that bats can be exposed to WNS both through the environment (soil in affected caves) or by contact with other bats. Research has also discovered that soil in caves where numerous bats have died from WNS contains spores of the fungus responsible for WNS. The big fear now is that as WNS moves farther south, it will start to impact huge bat colonies with more than a million individuals in a single cave. One sick bat could potentially spread this illness to an entire colony, wiping out huge numbers of bats. A cave I've worked with for many years in north Alabama has an estimated 1.5 million hibernating bats in the winter. If and when WNS impacts the cave, I don't know how I'll deal with the loss of such a huge number of bats I've come to love.

Many theories have surfaced to explain the sudden appearance of such a deadly affliction. Some suggested an association with pesticides or environmental contaminants, others suggested an invasive species. Many have noted the similarities to bee colony collapse disorder. Although nobody has an answer to why WNS suddenly appeared, one interesting study has shown a link to a fungus in France. When researchers first learned of this new fungus, scientists in Europe started to look around to see if any bats there had unusual fungal growth. French researchers found a bat with white fungal growth on its nose, sequenced the fungus, and it's a genetic match to Geomyces destructans. But, the bats since found in Europe with this fungus appear to be healthy and are experiencing no ill-effects from exposure to the fungus. The mystery deepens.

As researchers in the US spent more time studying affected bats, they also noted that not only does the fungus show up on bat noses, it also affects their wings. The damage isn't simply fungus growing on wings, rather infected bats have holes in their wing membranes, flaking skin, and even necrotic tissue. This means that even if a bat manages to survive a season after being exposed to WNS, the bat may have serious problems flying and hunting.

So what does all of this mean to us? Well, bats are essential components of our ecology and help control insects across the country. There are over 1,000 species of bats worldwide, and 40 species in the US. One bat eats half its body weight in insects every single night. One little brown bat can catch and eat up to 600 mosquitoes in one hour! A small bat colony will often eat up to a ton of insects nightly. If WNS continues to sweep across the country, not only will that mean we will lose many individual animals that are fascinating and useful, but our ecological balance will change. Without insects to help control insect populations, will another species fill the void?

I'm spending a ridiculous amount of time these days keeping up to date on WNS information and I'm sure I'll share more in future weeks and months. In the meantime, if you see bats acting in an unusual way (flying around during the day, flying during the winter, or on the ground flopping around), don't touch it. Instead, contact your state's wildlife biologist and/or your local animal control and report the bat. Trying to contact a biologist first. Animal control may not necessarily be aware of WNS and just assume the bat has rabies.

For more information, here are some resources:
And I need to include a cave picture so you can get an idea of why I like the underground world so much. My friend JV Van Swearingen IV took this picture many years ago.

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