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Kentucky aquatic snakes have high fungal disease prevalence
Aquatic snake species in Kentucky have high incidences fungal disease, which may affect their behavior without impacting their short-term survival.
“We did see that snakes — especially the queen snakes — were less likely to move. [The diseased snakes] tended to stay in the same spot,” said Steven Price, an associate professor of stream ecology at the University of Kentucky and one of the co-authors of a study published recently in Ecological Applications.
He and his colleagues had been capturing aquatic snakes around Lexington, Ky. for some time, implanting them with tracking devices so they could conduct mark-recapture studies. In 2014, they’d begun to notice lesions on many of the snakes. That and other signs pointed to snake fungal disease — an infection caused by a pathogen that has been found in more than two dozen snake species in the United States including Puerto Rico as well as Ontario, Canada. Researchers don’t fully understand how it affects serpents, but it can be deadly, and some studies show that it can drain the reptiles’ energy and dry them out.
In 2016-2017, Jennifer McKenzie, who led the study as part of her master’s work at the university, and her co-authors implanted PIT tags, or electronic microchips used for tracking, in 526 snakes from two species: queen snakes (Regina septemvittata), a species that feeds on freshly molted crayfish, and common watersnakes (Nerodia sipedon), a reptile found widely across eastern North America.
They determined the prevalence of the disease using photographs of lesions and genetic tests that identified Ophidiomyces ophidiicola, the fungus that causes the snake fungal disease called Ophidiomycosis. The large-scale study revealed that 40% of queen snakes and 20% of watersnakes had the disease.
“We have a high number of snakes that have the disease in our populations,” Price said.
To Price and his colleagues, the numbers weren’t surprising. They had already witnessed these high proportions of infected snakes in previous work. But he said that other researchers have been shocked about the high number.
But Price and his colleagues’ study didn’t seem to show that the disease was particularly deadly during their study year — diseased snakes didn’t die any more than non-diseased snakes. But he cautions that this could be due to the short length of the study, or to favorable environmental conditions during the study year. Some researchers believe that environmental conditions, like a wetter year or cooler air temperatures, can make the disease deadlier.
While some researchers have previously noticed higher numbers of deaths from the disease as the snakes emerge from their winter hibernacula, Price noted they didn’t observe a higher death rate in the spring in their study.
But they did notice some changes in snake behavior. Snakes that were infected with the disease seemed to spend more time basking and moved less. This could be a way for the snakes to conserve energy or even induce fever. Reptiles and amphibians can’t induce the fever conditions that help them fight disease automatically like warm-blooded mammals can, so they try to develop these conditions by using outside heat from sunlight or other environmental conditions.
“They’re essentially trying to fight this effect by heating up more, by inducing a fever,” Price said.
But Price noted another bias may occur when normally cryptic snakes bask out in the open more and are easier for researchers to spot than uninfected serpents. Researchers should be aware of these behavioral changes as they could lead to over estimations in disease prevalence in snake populations.
The mark-recapture work is ongoing, though, and Price hopes to be able to better answer questions of long-term survival as more data comes in from their study sites.