White-nose syndrome is a fungal disease caused by Pseudogymnoascus destructans that affects bats. It affects bats primarily in winter when they’re hibernating. Kate Langwig of the University of California, Santa Cruz (along with other researchers) is studying the disease at 30 different sites across North America. Six species of bats comprised her study sample that included winter hibernacula as well as (summer) maternity roosts. At each site, the researchers swabbed bats’ wings and faces and in the lab examined the swabs for signs of the white-nose fungus.

In a recently published article in the Proceedings of the Royal Society B (“B” for its biology edition), Langwig and her group present evidence that bats can successfully fight off the white-nose fungus from about May to mid-October. However, between November and May, when bats head off to their winter hibernacula, white-nose syndrome levels rise steeply. The winter surge appears to be due to two major factors: the conditions within the hibernacula and the bats’ lowered body temperatures.

Regarding the first of these factors, winter roosts, bats typically return faithfully to their over-wintering sites year after year. Once the sites become infected, they stay infected. And the fungus can survive for five years without ever entering its host. That means that a young bat can be free of the disease and become infected at its wintering site – or adult bats may fight off the infection during the summer only to be re-infected in winter when they return to the wintering site.

With respect to body temperature, when bats hibernate, they dramatically reduce their metabolic rate and thus also their body temps, typically somewhere in the range of the ambient temperature of their winter roost (often 15-21°C or 60-70°F). White-nose fungus appears to favor these lower temperatures as well as moisture levels present in many roosts.

How Does White-nose Kill Bats?

Once a bat becomes infected with the disease (by contact with the fungus on a non-organic substrate (e.g., the ceiling of a cave) or through contact with another bat) the fungus feeds off the skin of the infected bat, including its highly delicate wings. By affecting the bat’s metabolism, which attempts to fight off the disease, the bat wakes up more frequently and uses much of its limited fat reserves, often very quickly – and, of course, it’s not feeding during those winter months. Destruction of wing tissue may also lead to disruption of a bat’s water and electrolyte balance. Any or all of these may cause a bats death.

The Good and the Bad News

The bad news, aside from the disease itself, is that there is no current treatment for white-nose disease or an effective way to eliminate the fungus on a broad scale. This new understanding of the dynamics and seasonality of the disease could help scientists develop appropriate countermeasures including the determination of how and when treatments will be most effective.

Based on the study findings, the current timing of treatments is being re-examined. Many efforts focus on treating bats during the fall when they are active. However, it now seems like the timing is inappropriate if the treatment is not long-lasting. Also, treatments may be ineffective once the bats have lowered their body temperatures – the data from this study may provide important clues in terms of development of effective treatments as well as the timing of their administration. The best news is that bats that make it through the winter have a good chance to fight off the infection when their summer activity raises their body temperatures to around 35°C. (95°F), a good 15 to 20 degrees Celsius higher than the conditions that the fungus prefers.

If you’ve got questions about white-nose disease, contact us through our Web site contact page.

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