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A Plague of Snakes: But They’re the Victims

Posted by Richard Conniff on December 21, 2013

Black racer with fatal lesions

Somewhere in the back of our minds, we all worry about the sort of nightmare pandemic envisioned in films like Contagion or The Hot Zone, with some horrific new disease sweeping across the continents and mowing down human victims like so much hay. But wildlife biologists worry more than most, because they’ve already seen emerging diseases devastate two major animal groups.

Now it seems to be happening yet again, while the two other wildlife pandemics are still raging unresolved: Over the past two decades, the chytrid fungus has contributed to the extinction of perhaps 100 amphibian species—including some of the most colorful, charismatic frogs in the world—with many more extinctions now being predicted. White nose syndrome, another fungal disease, first discovered in 2006, has already killed off 6 to 7 million North American bats and now threatens some species with extinction. No reliable remedy is known for either disease.

The victims of what seems to be a new epidemic are snakes, and they may prove even harder to save, because they are widely unpopular and because populations in many areas tend to be small and scattered. Wildlife biologists first noticed the new pathogen in 2006, among New Hampshire’s only surviving population of the timber rattlesnake.

The first victim turned up dead in early June, from a severe fungal infection in the mouth. Other victims displayed skin lesions around the head and, in one case, a severely swollen eye. Within a year, half the population was dead.

Similar cases have appeared since then in snakes of various species in the Eastern and Midwestern United States. But because they live in the dirt, snakes carry a variety of fungi, and separating the pathogen out from among the background fungi has proved challenging, according to David Blehert, head of diagnostic microbiology at the U.S. National Wildlife Health Center in Madison, Wisc. Then, early this year, new molecular techniques made it possible to identify the likely culprit for what’s being called “Snake Fungal Disease.” Researchers then went back and determined that the suspected pathogen was present in virtually every known case of the disease to date.

So far the disease has turned up in nine states­: Illinois, Florida, Massachusetts, Minnesota, New Jersey, New York, Ohio, Tennessee, and Wisconsin. It has caused sickness and death in seven species: Northern water snake, eastern racer, rat snake, timber rattlesnake, massasauga, pygmy rattlesnake, and milk snake.

Federal and state officials are beginning work on a new grant from the U.S. Fish and Wildlife Service to survey snake populations for presence of Snake Fungal Disease. The aim is to avoid a repeat of the mistakes made in the early 1990s with chytrid fungus in amphibians. Because of inadequate monitoring, researchers failed to recognize that pathogen until it had spread widely and caused some species to become extinct.

No one knows yet where the new pathogen came from. It’s possible it was introduced from the pet trade or another source. Blehert thinks it’s more likely to be a fungus that was already present in the population, from which a more virulent strain has emerged, or a strain that does more damage because of changing weather conditions. The outbreak in New Hampshire occurred during the state’s wettest weather in 114 years.

The impact on snakes could be severe, Blehert warns, “because many of these threatened snake populations are already heavily fragmented and isolated from one another.” Amphibians may be somewhat more resilient in the face of chytrid fungus because they live in larger populations and lay thousands of eggs. But snakes tend to have much more limited reproductive potential. Timber rattlesnakes, for instance, give birth to live young, not eggs, and the offspring don’t reach sexual maturity for nine years. If fungal deaths pile up during those nine years, a population, or a species, could easily crash.

For now, the New Hampshire rattlesnake population seems to be hanging on. But researchers there warn that the combination of habitat fragmentation, loss of genetic diversity, climate change, and now an emerging disease could send some species spiraling into an “extinction vortex.”

One Response to “A Plague of Snakes: But They’re the Victims”

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