Bats, Fungi, and Mosquitoes

(Credit: Right Photo/ Al Hicks with the New York Department of Environmental Conservation)


Over the last two years some bat populations in the NE US  have been decimated for unknown reasons by what has been called white-nose syndrome. The name comes because a white fungus is often found growing around the nose of affected bats. So what is going on and does it matter? I mean not to be heartless but these are just flying rodents and they can carry the rabies virus. Well let's take the latter question first.

Does it matter? Yes it freaking matters! First, it matters because bats are fascinating mammals that use sonar to avoid objects and find food in the dark. Second, its never a good idea to ignore it when vast numbers of a group of animals starts dropping dead for no apparent reason. Are we susceptible? Our livestock? Our pets? Third, many bats are important for plant propagation as either pollinators (generally in climes warmer than the NE USA) and for seed dispersal by fruit eaters. Fourth, many bats eat mosquitos  and can eat a prodigious (elitist) number of mosquitos at that (on the order of 1000 mosquitos/hour/bat). Now a colony of bats is not going to effectively reduce the mosquito population enough to reduce human suffering (ie bites), but when you live in Minnesota every mosquito that dies is somehow reassuring.

Back to the first question, "What's going on?" Well the answer to this question is disheartening because we don't know. However, we know some things. First, we know there is a fungus growing around the nasal cavities of many afflicted bats. This means......not much sadly. This fungus could be a normal part of the flora (elitist) that lives in low numbers on the skin of bats normally, also known as a commensal. In this case, the large large amount of fungus observed to be growing around the nose could reflect some underlying immune dysfunction due to toxins, other pathogens, etc. In this case the fungus is not the cause of disease but a symptom. (A runny nose does not cause a cold, it is simply a symptom of a cold.) Second, we know the bats' hibernation patterns are screwed up, they wake up early or do not wake up.

Alright this is really old news (Spring 08), why post about this now? Well, the Oct. 30th  Science Express has a paper from Blehert DS, Hicks AC, and colleagues describing the identification of the fungus associated with white-nose syndrome. In short, the fungus is a member of the Geomyces family, a cold loving (psychrophilic) family of fungi related to baker's yeast (Saccharomyces cerevisiae). Now the fact that a cold loving fungus is infecting bats in cold environments (bat caves in NE USA in the winter hover around 4°C) is interesting. However, is this fungus the cause of white-nose syndrome or an effect? Ok, it is THE cause of white-nose syndrome, since white-nose syndrome is the growth of fungus around the nose. The question is, is the problem with bats leading to white-nose syndrome or is white-nose syndrome the problem with bats? We still don't know. However, the authors, correctly Ill add, remind us that fungi (chytrids in this case) have devasted frog populations. So this is an important step forward. Now that we know what we are dealing with, we can ask if the fungus is causing disease or not. Geomyces species have caused disease in people and other mammals so it is not implausible however it is early to give a definitive response.