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:
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.