Effect Measure

Bats and fungus

The caves in the Dordogne department in southwest France are most famous for paleolithic cave paintings at Lascaux (the Dordogne is also famous for the being the home of microdot, whose blog The Brain Police is one of my daily reads). Now it has yet another claim to fame: the discovery of the first bat outside of the northeastern United States with White Nose Syndrome (WNS) Fungus (Geomyces destructans):

Biologists are struggling to understand a recent emerging infectious disease, white-nose syndrome (WNS), which potentially threatens >20% of all mammalian diversity (bats). WNS is a deadly epidemic that has swept through the northeastern United States over the past 3 years and caused the death of >1,000,000 bats, with decreases of ≈100% in some populations.

This disease is associated with hibernating, cave-roosting bats. A visually conspicuous white fungus grows on the face, ears, or wings of stricken bats; infiltration of the hyphae into membranes and tissues leads to severe damage. Bats that exhibit WNS have little or no fat reserves, which are essential for their survival throughout and after hibernation. The fungus associated with WNS is a newly described, psychrophilic (cold-loving) species (Geomyces destructans) (Puechmaille et al., Emerging Infectious Diseases [cites omitted]).

I’ll be honest. Bats scare me, mainly because of rabies. Most recent cases of human rabies in the US have been associated with bats. But bats are an essential part of the ecosystem and voracious consumers of insects. Removing bats from the ecosystem perturbs the balance between insects and the rest of the system with unknown and unpredictable consequences for agriculture and human health. So when an emerging infectious disease comes along and wipes out the cave dwelling bat population it’s not just something that conservation biologists worry about but also agronomists and public health specialists.

It turns out there are an amazing number of different kinds of bats and they apparently represent a sizable fraction of mammalian diversity (what fraction seems hard to estimate; this paper actually cites two figures, >20% and >25% of mammalian diversity, citing the same source for each figure! I tried getting a better fix but wasn’t successful, although biodiversity isn’t my area of expertise. I’ll just assume it’s a goodly proportion and not worry about the least significant figure.) And as noted in the pull quote above, they are dying like flies (sorry; couldn’t help it) in the US northeast. And it’s not clear what’s killing them. One of the working hypotheses is White Nose Syndrome Fungus. Here’s what it looks like:

i-3b8a3aefef46a3fc17e980e597428ae9-Batnoseonly.jpg

But now the story gets a bit complicated. The picture is of the French bat (Myotis myotis) in the Dordogne (near Périgueux). It was found in the course of a monitoring study of hibernating bats last March. Culture and genetic study of the powdery growth confirmed it was WNS Fungus, but this bat seemed healthy, had good weight and was the only bat affected. So if WNS fungus is the agent that is killing bats in the northeast of the US and not just an accompanying infection to another disease (and so far, intensive study for other bacteria, fungi and viruses has revealed no other cause), then three possible explanations for this singular and apparently healthy French bat present themselves:

The first scenario is that the fungus has only recently arrived in Europe and all bats in Europe are now at risk for infection. Thus, conservation steps must be taken to minimize the spread of this disease, especially because this disease is specific for hibernating bats. After the hibernation period, M. myotis bats may migrate up to 436 km to reach their summer roosts, a behavior that could quickly increase the chance of fungus transmission. A second scenario is that the fungus has been present in Europe for a long time. Because mass deaths have not been observed in bats in Europe, these bats may be immune to WNS. Therefore, identification of mechanisms of this immunity will advance understanding of this disease and fungus resistance in mammals. The third scenario is that the G. destructans fungus is not the primary cause of death but acts as an opportunistic pathogen in bats already immunocompromised by other pathogens such as viruses or bacteria. Comparison of pathogens in bats in Europe and the United States infected with G. destructans should identify the primary causative agent. [cites omitted]

Because the French bat wasn’t underweight, the authors favor explanations two or three. Loss of weight with insufficient fat to carry the animal through hibernation is characteristic of WNS in the US. They’ve been monitoring hibernating bats for 6 years at this site and 5 more in a 2 km radius and never seen any other WNS or die-offs. Still, this could also be evidence it is new to Europe, so the rejection of scenario 1 seems based solely on the condition of a single bat with WNS, which seems a bit risky to me.

The great bat die off in the US and this new piece of evidence are a fascinating scientific mystery with potentially great practical importance. It will remain for others to unravel,however. Bats still scare me.

Comments

  1. #1 Tymbuktu
    December 30, 2009

    Wow – Frogs, bees, bats. The first and last eat a lot of Mosquitos. Mosquitos scare me. Especially as they expand their habitats.

  2. #2 microdot
    December 30, 2009

    If the fungus exists here, then it would seem reasonable that it is the third hypothesis and it seems that it is the same with humans…
    I see a lot of bats here and my barn is host to a healthy population. They are pretty active any night the temperature is high enough for them to come out of hibernation.
    I have become an expert in getting them out of rooms when the fly in through an open window at night…
    The secret? don’t do anything, just shut off the lights and leave the room. They instantly find their way out.

    This region is relatively unpolluted, very clean air and no industry, but the modern age intrudes a little more every day. If the white funguis is a recent phenomena, then it would seem that it is opportunistic and as the environment deteriorates, it proliferates and as it proliferates, it attacks the bats immune systems and creates the conditions for other problems.

    We are beginning to have problems with bees here as well.

  3. Now wait a minute. That webpage you cited for bat-induced rabies only has 1 (one) confirmed case caused by a bite. I do agree that many of the cases might have been sourced by a bat, even so, there is no reason to be “afraid” of them because of it. Bats infected with rabies are very unlikely to bite a person (as shown on the webpage), and usually end up paralyzed instead of aggressive. What’s more likely is that an infected bat is eaten by another animal that then bites humans.

    If anything, you should be more afraid of any dogs/cats/raccoons you see than any bat.

    And to place it all in perspective, West Nile Virus kills 10x the people as Rabies (30 last year for WNV vs 3 for Rabies). So do you put on DEET every time you step outside?

    @1, my big worry isn’t increased disease due to mosquito born illnesses, but crops or trees getting devastated due to insects. Climate change is allowing the Pine Borer Beetle to devastate the pine forests of the north and higher mountain elevations. Who knows what kind of repercussions taking out a major top level predator (for night flying insects anyways) will have on the environment? Look at the effects of taking away, and then restoring, wolves to Yellowstone, or the ecosystem changes wrought by the mass killing of sharks for soup, or how climate change is allowing the Mountain Pine Beetle to devastate the northern forests.

  4. #4 Joseph O'Sullivan
    December 30, 2009

    “Bats still scare me.”

    I was at a lecture last year at the Museum of Natural History in NYC. The speaker was a NY Department of Environmental Protection ecologist. He monitored bats for many years, and he was afraid for the bats.

  5. #5 revere
    December 30, 2009

    facebook: Well, epidemiologically it’s bats that give rabies to people, even though raccoons and foxes and skunks have more of it. They don’t fly into my house, though. But I didn’t say it was rational. As for WNV, etc., the issue with rabies is that it’s a death sentence once you start showing symptoms (yes, I know there are one or two survivors in the medical record but it’s very, very rare).

    Joseph: That’s undoubtedly true. The bats have more to fear from me that I do from them. If they were rational and I were rational.

  6. #6 raven
    January 1, 2010

    I’ve been following the bat white nose disease loosely.

    It is somewhat myterious in that it isn’t clear that the fungus is anything more than an opportunistic pathogen. The P. carinii of the bat world.

    Same thing for bee colony collapse disorder. Some researchers think it is a consequence of pushing bees too far. Exacerbated by a narrow genetic base of commercially bred bees.

  7. #7 Susan Och
    January 1, 2010

    So does everybody think bats are scary? Or is there human-facilitated intercontinental bat travel?

    Or are cave explorers spreading fungus around? I can still buy bat guano from a garden supply catalog, I wonder if that’s shipped from one hemisphere to another?

  8. #8 Joseph O'Sullivan
    January 1, 2010

    “Or are cave explorers spreading fungus around?”

    That was a concern the speaker (from the NY State Department of Environmental Conservation, not the NY City Department of Environmental Protection) raised in the syndrome’s spread from upstate NY to neighboring states. The DEC had closed off several caves to block cave explorers, to the extent of installing barriers.

  9. #9 Eric Johnson
    January 2, 2010

    That bat could have something like a hypofunctional or nonfunctional TLR allele. This sort of thing can be the cause of herpes encephalitis in humans that otherwise have normal survival rates.

  10. #10 Virginia
    January 4, 2010

    We have a large and persistent Bat colony in the attic of our Upstate NY home. Attempts to encourage them to move elsewhere have failed but the WNS Fungus seems to be reducing their numbers. I have actually worried more about histoplasmosis with bats sharing our space than about rabies. Our dog is an excellent bat spotter when one actually gets into the living spaces of the house. Unless I have seen the bat fly in and know that it hasn’t had contact with our dog, cats or children, I trap it, place it in a canning jar and stick it in the freezer until I can take it to a local vet for rabies testing. In 8 years with approx. 3 bats per year, we’ve never had one turn up positive, but bat rabies was on the rise in St. Lawrence County the last two years.

    If you find a bat in your home that may have been in contact with people or pets, you should not release it – trap it, freeze it and call Public Health. They will direct you to a drop off place for the bat so that it can be tested. Be aware that some bats will wake up on the way to the drop off location so keeping it in a sealed glass canning jar or sturdy plastic container is a good idea.