America’s bats: in danger!
The latest issue of Microbe magazine arrived in my mailbox the other day, with a fascinating article about the epidemic of White-Nose Syndrome among bat colonies throughout the northeastern United States. Biologists first noticed in 2007 that bats in several caves near Albany, NY were dying during their winter hibernation. According to the report in Microbe, it has been estimated that more than 1 million bats have died from this epidemic to date, and that one extremely common species of bat, Myotis lucifugus, could become extinct within the next two decades if the epidemic continues.
Initial work has been to identify the causative agent of White-Nose Syndrome, and a novel fungal species, Geomyces destructans, has been proposed to be responsible. Infection with this fungus causes an invasive skin disease (noted in picture “B” to the right), initially by colonizing the superficial layers. Later penetration of deeper layers by the hyphae (filaments) of the fungus leads to the formation of ulcers damaging the function of the wing.
The origin of G. destructan is at present unclear, although molecular evidence suggests that the fungus was accidentally introduced possibly by a tourist into a cave in New York. The fungus has been isolated from many sites in Europe, and polymerase chain reaction (PCR) analysis has indicated that many hibernating bats in Europe have been infected with the fungus. Unlike hibernacula in the United States, the European bats have not shown the precipitous decline in numbers that biologists are currently observing here. This raises the interesting question: what is different in the interaction between North American and European bats, and why is the interaction with the fungus leading to such a drastic difference in outcome?
Bats appear to only be colonized while they are hibernating, when their core body temperature is lowered. As seen in this image from the article in Microbe, G. destructans shows a marked tolerance for cold temperatures, and in fact shows an optimal growth rate at around 12 degrees Celsius. The fungus actually is not able to grow at all at temperatures above 20 degrees Celsius (66 degrees F). This helps to explain why hibernating bats are more susceptible to infection, but does not help to explain why North American bats are more susceptible. Future research will likely focus on genetic differences between the bat species (are there differences in the innate immunity of the various bat species?), variability between the North American and European isolates of G. destructans (is the North American isolate somehow more virulent?), or even behavioral differences between bat colonies.
Biologists are looking for ways to stop the epidemic, but stopping a virulent pathogen in a wild population such as bats poses a number of issues. One possibility would be to decontaminate afflicted caves, however this is unlikely to be successful as the toxic side effects of chemical control methods for fungi would likely have severe repercussions on other organisms in the ecosystem. Because of the numbers and distribution of the afflicted animals, it is also logistically unlikely to propose to individually treat animals exhibiting symptoms. One positive step that can be taken would be to limit the transfer of the fungus between caves; this would require limiting access by humans to places where bats roost and hibernate, but could have a positive effect on slowing the rate of expansion of the pathogen.
Posted on June 28, 2011, in Microbes in the News, Sad and tagged Geomyces destructans, Little brown bat, United States Fish and Wildlife Service, White nose syndrome. Bookmark the permalink. Comments Off on America’s bats: in danger!.