In 2008 biologists studying the eastern massasauga rattlesnake (Sistrurus catenatus catenatus) made a gruesome discovery: three sick snakes suffering from disfiguring lesions on their heads. All three died within the next three weeks. A fourth snake, found in 2010, also died from the mysterious growths and ulcers.

Necropsies uncovered the source of the lesions: a fungal infection called Chrysosporium. "Chrysosporium causes disease in bearded dragons and in other snakes, and it's a bad bug," according to Matthew Allender, visiting instructor at the University of Illinois at Urbana–Champaign, speaking in a prepared release. "We see it in captive animals worldwide, but we don't typically find it in free-ranging animals." Allender is the lead author of a paper on the fungal infection, which appears in the December 2011 issue of Emerging Infectious Diseases.

The infected rattlesnakes were all found in a park near Carlyle Lake, Ill., where a long-term monitoring program has been studying the eastern massasauga since 1999. The four snakes' heads were covered in ulcers and swelling that extended throughout their skin and skeletal muscles, and obscured their nasolabial pits. One snake had an infected eye, with only a small fragment of its cornea remaining. The snake with the most severe infection suffered from extreme swelling around the maxillary fang.

Further testing revealed that the Chrysosporium fungi were molecularly related to samples from the diseased skin of a captive black rat snake. This suggests that the fungus could have come from released or escaped pet reptiles.

Allender first reported on his findings at a meeting of the U.S. Fish and Wildlife Service (FWS), after which he heard of similar infections that have occurred in other parts of the Northeast over the past five years. "They seem to be having a similar problem in timber rattlesnakes in New Hampshire and Massachusetts," Allender said.

Allender called the Illinois infections a "yellow flag" that shows a need for further study.

The eastern massasauga, one of the smallest rattlesnake species, is a candidate for protection under the U.S. Endangered Species Act. It currently has no federal protection, although it is protected by state laws throughout its habitat, which extends from western New York State to southern Iowa. According to the FWS, the snake is threatened by destruction of wetlands and persecution by people who have an innate fear of venomous snakes.

Carlyle Lake is home to the only viable eastern massasauga rattlesnake population in Illinois, according to a report published in 2000 by the Illinois Natural History Survey.

Photo: United States Geological Survey (pdf)