Snake Fungal Disease Found in Louisiana

Wild snakes play important roles in ecosystems as both predator and prey. They provide direct benefits to humans such as consuming crop-destroying pests. Snakes are efficient predators upon various rodents, which may damage property, ruin crops and spread disease. In addition, snake venom research has provided several medicines that are used to halt heart attacks and prevent blood clots and continues to show promise in other areas of medicine.

“Snakes may not be everyone’s favorite animal, but they are undeniably important in a well-balanced ecosystem,” said USGS Ecologist Brad “Bones” Glorioso, lead author of the study. “They deserve our respect and understanding.”

SFD is characterized by scabs or crusty scales, nodules below the skin, cloudy eyes, abnormal molting, and areas of thickened skin. Snakes infected with SFD, besides being lethargic and lacking an appetite, will attempt to bask in the sun to raise their body temperatures despite unsuitable conditions. This behavior, in addition to the fact that infected snakes are often in poor body condition, makes them more vulnerable to predators.

“SFD is an emerging threat to wild snake populations particularly in the eastern United States,” Glorioso added. “We don’t know yet how the disease affects various species, but in at least one species, an estimated 80 to 90 percent of infected snakes die from the disease.”

In Louisiana, the first confirmed case of the disease was in a juvenile snake from the Cypress Island Preserve near Lafayette. It is one of the few documented cases in the US of the disease in a juvenile snake.

“Finding the disease in a juvenile snake is of particular concern. If younger snakes die from the disease before reaching reproductive age, it could have devastating effects on snake populations,” said Glorioso.

Since completing the initial study, the researchers have confirmed the presence of the disease in snakes from other locations in the state.

In the last two decades, fungal and fungal-like diseases, including chytridiomycosis in amphibians, white-nose syndrome in bats, and colony collapse disorder in bees, have caused some of the most severe die-offs and extinctions ever observed in wild species.

USGS scientists recently identified the specific fungus responsible for causing snake fungal disease.

The disease was implicated in recent die-offs and declines in populations of two protected species of pit viper in the Midwest and Northeast. In Midwest populations of the massasauga, a candidate for federal listing under the Endangered Species Act, infected snakes have an estimated 80 percent to 90 percent mortality rate. Mortality rates of infected timber rattlesnakes in the Northeast are estimated between 30 percent and 70 percent.

To date, the disease has been confirmed in at least 14 snake species including the northern water snake; racer; rat snake; timber rattlesnake; massasauga; pygmy rattlesnake; milk snake; plains garter snake; mud snake and southern water snake. It is believed to be more widespread than is currently documented as snakes showing signs of infection have been reported in other states and in other species.

The authors have begun a more detailed capture-mark-recapture study on snakes at Palmetto Island State Park that includes taking swabs of all snakes, including those that appear healthy, to be tested for the presence of the fungus that causes SFD. This protocol will allow them to model survival probability based on whether the snake was positive or negative for the fungus, and to determine population trends.

The study, “First Documented Case of Snake Fungal Disease in a Free-ranging Wild Snake in Louisiana,” was published in Southeastern Naturalist.