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Fungus May Be Culprit In Deadly Bat Epidemic

JOE PALCA, host:

This is Talk of the Nation: Science Friday from NPR News. I'm Joe Palca sitting in for Ira Flatow. A few years back, people in Upstate New York started to notice brown bats cruising for insects in broad daylight, in the middle of winter. Of course there aren't any insects in the snows of February when the bats should be hiding out in the caves, living off their fat stores until the spring. So state scientists went to check out some caves near Albany hoping to find an explanation for this unusual winter excursions by the bats, and instead what they found was thousands of dead bats. The ones still alive were emaciated and had a mysterious white substance on their noses. The next year, these die-offs had spread to caves in Pennsylvania, Vermont, Massachusetts, and Connecticut and scientists aren't sure how or why.

But my next guest has been doing some detective work in the lab trying to figure out what's killing off these bats, and let me introduce him. He's name is David Blehert. He is the head of the Diagnostic Microbiology at the United States Geological Surveys National Wild Life Health Center in Madison, Wisconsin. And he joins us on the phone today from Wisconsin. Welcome to the program, Dr. Blehert.

Dr. DAVID BLEHERT ( Head of the Diagnostic Microbiology at the United States Geological Surveys National Wild Life Health Center in Madison Wisconsin): Thank you very much, Joe. Happy to be here.

PALCA: And if you want to join the conversation. Give us a call. Our number is 800-989-8255 that's 800-989-TALK. And if you want more information about what we're talking about this hour, go to our website at where you'll find links to the topic. So, just recently there's a paper by you and some colleagues in Science magazine that looks at this white substance and maybe has identified it. So what is the white substance that they found on the bat's nose?

Dr. BLEHERT: Right, so what we found is a fungus that belongs to the genus Geomyces, which is actually a common soil fungus around the world involved in the decay of organic matter. The one that we've isolated from bats, we believe has some unique properties that may have allowed it to emerge as a new pathogenic threat to bats in the Northeast.

PALCA: So well first of all. I mean would people have noticed this if it had been occurring on bats before, or is this is something that they're sure that this is a unique experience for bats to be infected with this fungus?

Dr. BELHERT: I think that we can be fairly certain that this is a unique thing among bats. So for example there is a species of federally listed endangered bats, the Indiana myotis or Indiana bats. And so Indiana bats for example in New York State, their hibernation caves are surveyed every other year. And literally, every single bat they find in the caves is photographed and counted.

PALCA: Uh huh.

Dr. BELHERT: So people are out there monitoring.

PALCA: So this would have been noticed if it - I mean it would've been picked up if it had occurred before. So that suggests that it's related, but I guess the question is you know is this a cause or an effect of the bats whatever is doing in the bats.

Dr. BELHERT: Right, and that still does remain somewhat of a question. We have our hypotheses on this, and some of us favor some over others.

PALCA: Well what would be - what would be the mechanism that a fungus on a bat's nose would be lethal?

Dr. BELHERT: Right, so first of all it's much more extensive than just a bat's nose, that's perhaps the most visible manifestation which led to the name for the disease, 'white nose syndrome.' But we also do find the fungus growing on other exposed skin surfaces such as the ear, pinna, and then perhaps most importantly the wings, which, wings are critical for flight, and flight is critical for feeding. So severe damage to the wings, if it affects the ability of the bats to fly through scarring or holes that the fungal infection puts in the wing…

PALCA: I see.

Dr. BELHERT: Once the bat emerges from hibernation, this could then impact its ability to effectively feed.

PALCA: Uh huh, uh huh. So this may be a problem that's actually occurring during the warmer months. But they're experiencing this - they're experiencing the problem during the cold months and they're forced to go out and try and feed some more.

Dr. BELHERT: Well actually - so we have actually characterized this disease as a disease of hibernation. So one of the properties of the fungus is that it's what we call a psycrophile or cold loving fungus. So it selectively only grows at cold temperatures. And these are temperatures that are fully consistent with the Huron(ph) temperatures of the bat hibernation caves, which is about the same as the temperature within your refrigerator. So once the bat, if the bat survives fungal infection and emerges in the spring, they warm up their body temperatures by activating their metabolism.

They move to warmer environments. I don't think that those warmer temperatures would kill the fungus, but it can't actively grow at those temperatures. So effectively during the summer, I believe that the bats are capable of still spreading the fungus among each other, but they do have this opportunity potentially to mount some recovery to damage done during hibernation.

PALCA: OK, well let's take a call now from one of listeners. And again the number is 800-989-8255. Let's go to Ron in Amherst, New Hampshire. Ron, welcome to Science Friday.

RON (Caller): Hi, thanks. I was wondering, I know there's been an outbreak of rabies in different animals, raccoons and - I understand - I know I out in Michigan, bats and rabies are big problem. If rabies could be involved in this? You know, I know, rabies can cause unusual behavior in animals and things like that. But you said you didn't know if the fungus was the cause or the effect. You now maybe, could rabies be involved?

PALCA: Interesting question. What about that?

Dr. BELHERT: Right, so we actually, I think, can fairly confidently say that rabies is not involved. Rabies does exist at low incidents among insectivorous bats, or insect feeding bats, like we would find in the Northeastern U.S. But as a matter of fact, virtually all of these animals that have come to the laboratory have been tested for rabies and they've all been negative. Something else worth noting is one of the initial observations that something was wrong in the population is bats that gets tested for rabies are generally bats that are aberrantly behaving, a manifestation of some of the neurological effects of the rabies virus infection.

And what was noticed at the New York State Department of Heath, where rabies testing is done, was that they're rabies infections of little brown bats, the primary species infected by the fungus, spiked to about 25 - about ten times the 25 year average for the winter month. So really there should be no bats coming through rabies lab in the winter because the bats are all hibernating away in their caves, but with bats flying around and dying on the winter landscape, a lot of those animals are being submitted for rabies testing.

PALCA: Interesting.

Dr. BELHERT: And once again they were all negative.

PALCA: Interesting OK well we'll have to look for another explanation. Let's try - let's go to another call now and go to Paul in Provo, Utah. Paul welcome to Science Friday.

PAUL (Caller): Hi, thank you. This is really intriguing. It was mentioned that the bats were found dying in one place, I think it was Albany, and then they were found with the same malady in another geographic area nearby, and it makes me wonder if you have tried to trace this fungus through insects whose larvae emerged from the ground or various terrestrial sources. And that's maybe they are transmitting or transferring this fungus from one geographic area to another based upon natural migrations, or winds patterns, or something like that rather than it being contagious from bat to bat.

PALCA: Interesting Paul. What do you think about that David Blehert?

Dr. BLEHERT: I actually think that's a good idea, and potentially we could look at some of the newly introduced invasive insect species to the regions, such as the introduced gypsy moths for example. So that is something we've talked about. And if does turn out to be primarily pathogenic fungus that was introduced, there is many means by which it could have introduced, starting with humans, ranging to some animal species, to an insect species, even to wind- borne dust.

PALCA: Interesting. We have a question from somebody called Kanis Luming on Second Life who says, is there an emerging infectious disease? Is this an emerging infectious disease that might be applicable to other mammals? Any - is this an opportunistic infection that's grabbing bats selectively or could it be other mammals?

Mr. BLEHERT: Right. Well, once again, one of the important properties to consider here is that this fungus cannot grow above about 65 degrees Fahrenheit. So, humans and most other warm-blooded mammals, for example, have an internal body temperature and even a very warm skin temperature somewhere around 98.6 degrees Fahrenheit. So, right now, I would consider it a potential concern for hibernating animals that drop their core body or skin surface temperatures down to below 70 degrees Fahrenheit - even in the 40 degrees Fahrenheit ranges, where this fungus grows optimally. I don't think it possess a threat to humans.

PALCA: No, no. From what you describe, it doesn't sound like it would. OK. Let's try another call now and go to Daniel in Denver, Colorado. Daniel, welcome to Science Friday.

DANIEL (Caller): Thanks. First of all, I am not a scientist, but I am just trying to find a little bit of common sense right here. Here in Colorado we have a pine beetle killing out millions of pine trees because of what is believed to be a direct result of global warming, where the pine beetle is actually surviving higher temperatures than normal in winter time, so that allows it to attack and kill the trees right here, the pines in this particular point. The first question is, why is this fungus able to attack these bats, and what was different before that it wasn't able to attack them?

That would the first question, the second one is, could there be a relationship between higher temperatures, because due to global warming and the worst case scenario is, what happens if the entire population of bat, I doubt that this is going to happen but if the deaths - if they do get wiped-out, what would the direct impact be on humans?

PALCA: OK, Daniel, I have to get David Blehert to answer that quickly because we are almost out of time for this segment but global warming causing this infection or why now? I guess, were the two big questions.

Mr. BLEHERT: Right. So, why now? So, first of all, we do have to consider that perhaps this fungus was recently introduced and if so, that's why now. It's a new introduced pathogen that's just emerged as a problem. Alternatively, there could be some environmental perturbation that in the Northeast region that has allowed a fungus that was always present in the environment to emerge as an opportunistic pathogen. With regard to global climate change, that certainly is something we all consider.

We don't have - I need to emphasize - we don't have any data to indicate such, but if we really want to go out on the limb and speculate, Geomyces fungi have been discovered in Antarctica associated, for example with an Antarctic birds called skuas. You know, one could go out on the limb and hypothesize that, if you want to get science fiction on this, that maybe this is something that was once locked in Arctic permafrost, and then with the decrease of Arctic permafrost, was liberated and, you know, perhaps then brought southward through animal migration.

PALCA: Well, as you say, it's an interesting speculation but we'll have to leave it there because we're out of time. Thank you David Blehert, he is the head of the Diagnostic Microbiology at the United States Geological Survey in Madison, Wisconsin. Stay with us, we have more to talk about on bats when we come back after this break. This is Talk of the Nation from NPR News. Transcript provided by NPR, Copyright NPR.