A mysterious infection is killing the snakes of the eastern US

Over the course of two years in the early 2000s in Florida, 42 pygmy rattlesnakes turned up dead. Then 59 more. At the time, the culprit wasn’t identified, but researchers now think that a deadly fungal infection is spreading among the snakes of the eastern US.

The “snake fungal disease,” or SFD, has now been identified in at least 15 states, and it isn’t pretty. Pitvipers called Eastern Massasaugas, a type of rattlesnake, turned up in Illinois in 2008 with severe skin lesions and swelling. Eventually the infection crept into the snakes’ muscles and bones. In 2006, a population of timber rattlesnakes in New Hampshire showed the same symptoms. Prior to the outbreak there were at least 40 individuals in that population. Only 19 survived.

Other types of snakes suffer differently. Garter snakes, rat snakes, and ribbon snakes have all also succumbed to SFD, but the infection works differently in these nonvenomous serpents. They get pneumonia and eye infections, and at least one garter snake also suffered a liver infection.

There’s not much known about the fungus that causes SFD, a species called Ophidiomyces ophiodiicola, or Oo. Together with his colleagues, University of Illinois researcher Matthew C. Allender set out to try to better understand just how this mysterious snake-killing fungus works. They published their findings last week in the journal Fungal Ecology.

It turns out that Oo survives by eating keratin, the substance out of which human fingernails, rhino horns, and snake scales are made. Researchers have never found an infected snake that survived its infection; “mortality,” writes Allender, “appears to be 100 percent.”

According to Allender and his colleagues, the fungus thrives just fine in soil and appears completely satisfied gobbling up dead animals and plants. What they don’t know is why it’s attacking living snakes, but they suspect it’s mostly opportunistic. After snakes emerge from hibernation, it takes some time for their immune systems to kick into high gear. That’s the perfect time for a fungus to move in and feast on their scales.

While herpetologists are concerned about the effects of the infection on individuals, the bigger concern is about the role that the fungus might play in population declines. And as global temperatures increase, snakes are expected to become even more susceptible to infection by Oo, especially in parts of the world where winters will become milder. That’s because the fungus’s growth appears to be slowed as its environment cools towards freezing.

Auburn University herpetologist David Steen agrees that the spread of SFD is cause for concern. “Reports of fungus on snakes started trickling in a few years ago, and there has been some concern that this represents a new emerging threat,” he said. But he points out that it’s possible that the fungus has been around for quite some time, while researchers have only recently become aware of it. The problem is that nobody really knows. Steen says that this study represents an important early effort to learn more about the fungus.

Looking to the future, Allender identifies two critical priorities. The first is for epidemiologists to continue monitoring the spread of SFD, especially because snakes are so popular in the global pet trade. The containers used to breed and house snakes are ideal places for SFD to proliferate and to jump from species to species, so animal control and customs agents need not only to be aware of the potential threat but also need better, rapid methods to test for the disease. The second is for an effective treatment, something that has not yet been uncovered.

To understand just how devastating a fungal infection can be, one need look no further than white-nose syndrome, which is wiping out bats in the eastern US, as well as the chytrid fungus, which affects frogs and salamanders all over the globe. While massive die-offs in snake populations have not reached the levels seen for frogs and bats, “snakes are extremely difficult to survey and populations could decline precipitously and in most cases we would have no idea,” said Steen. “It is concerning that of the few intensively monitored pit viper populations, some did decline and a fungus is a potential culprit.” – Jason G. Goldman | 08 July 2015

Allender, M. C., Raudabaugh, D. B., Gleason, F. H., & Miller, A. N. (2015). The natural history, ecology, and epidemiology of Ophidiomyces ophiodiicola and its potential impact on free-ranging snake populations. Fungal Ecology. DOI: 10.1016/j.funeco.2015.05.003.

Header image: Juvenile timber rattlesnake, via shutterstock.com, ©Evin T. Carter