White nose in the winter

Since its emergence in 2006, White Nose Syndrome (WNS) is responsible for the deaths of millions of North American bats during the winter months. If you don’t know what it is, White Nose syndrome, is caused by a fungal infection, Pseudogymnoascus destructans (Pd for short). Until recently the only way to irrefutably identify WNS was to euthanize the bat and analyze its skin in the lab. However, a report published this past summer in The Journal of Wildlife Disease reveals that an old diagnostic tool for human ringworm can be re-jigged as a wildlife management tool: UV fluorescence.

UV light, causes ring worm sites to glow fluorescent, making it a handy diagnostic tool for fungal infection. This technique doesn’t detect all fungal infections, which is handy because otherwise researchers would get a lot of false positives. In the case of the bat researchers, they were able to positively identify Pd infection using fluorescence very precisely.

Bats suffer casualties from this infection during the winter months when they should be hibernating in caves. Victims of the disease display unusual behaviors: being awake, moving towards the mouth of the cave, and attempt daytime flights. Like most mammals, bats hibernate in the winter because there is a lack of food. When infected bats perform these strange behaviours, not only are they risky and can result in predation, but they burn precious calories that they cannot replace if food is scarce. The majority of WNS victims are emaciated upon discovery and researchers to believe that starvation is the actual cause of death from WNS infection; and the number of mortalities is staggering. Since its emergence, WNS is believed to be responsible for the deaths of 5.7 – 6.7 million bats. The U.S. Fish and Wildlife Service is concerned that this invasive fungus could bring about the extinction of some North American species.

After the disease was first documented in North America, researchers scrambled for a way to identify infected populations. The disease’s name-sake, white fuzz growing on the bats’ faces and wings, is a symptom but not a reliable indicator for infection, especially in the early stages. But, Pd lesions consistently fluoresce orange-yellow under UV light and this study has found that UV light is effective as a way of assessing wild population.

The first step was to determine how comparable field observations were to in the lab. Wings from bats from WNS positive areas were sent to the United States Geological Survey Wildlife Health Center. Under lab conditions, bat wings with fluorescent orange-yellow spots tested positive for WNS when the cells were examined under a microscope. Bats that had not fluorescence were negative for WNS infection.

The next step was to evaluate the technique’s effectiveness at identifying WNS in the field and to develop a harmless evaluation tool. Bats from caves in both the U.S.A. and Czech republic were checked with UV light for the orange-yellow WNS fluorescence. Fluorescent sites were circled on the wings and the animals were sent to the lab for testing. The fluorescent spots highlighted in the field match perfectly with spots of WNS cell damage under a microscope. The technique is so accurate that a 3 mm biopsy of the fluorescent skin will test positive for WNS in the lab.  This is great news because the animal suffer minimally from the biopsy and just fly off.  With this new technique, not only can researchers screen bats in the field, but also they can identify specific sites for non-lethally biopsy.

Identifying infected populations is just the first step. Current estimates suggest that there has been an 80% reduction in bat populations in areas affected by WNS and as of now, there is no cure. Bats play an important role in global ecosystems and in our global economy. Some act as pollinators and seed distributers. Others are voracious consumers of insects, some of which are human pests. This new UV technique will allow researchers to quickly and non-invasively track the spread of the disease, which provides vital data to inform management strategies.

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