Snakes around the world are increasingly facing the threat of extinction, with disease emerging as a major concern alongside habitat loss. One of the most serious illnesses affecting snakes is ophidiomycosis, commonly called snake fungal disease, which is caused by the fungus Ophidiomyces ophidiicola (Oo). Since researchers first identified the disease about 20 years ago, it has been detected in many snake species.
In an effort to better understand the overall health of wild snakes, researchers in the southeastern United States investigated seven different pathogens in native snake populations. Their goal was to compare infection rates across species, locations, and time periods. The findings were published in Frontiers in Veterinary Science.
“The fungus Oo and the parasite Raillietiella orientalis (Ro), appear to be the most important infectious agents in free-ranging snakes in the southeastern US,” said first author Dr. Corinna Mishin (formerly Corinna Hazelrig), a researcher at the University of Georgia. “We also show that increased risks of ophidiomycosis was strongly associated with coinfections in free-ranging native snakes.”
Researchers Survey Hundreds of Wild Snakes
The study, funded by the Morris Animal Foundation, involved sampling more than 500 snakes from two wildlife refuges in South Carolina and Florida, covering 29 species. Researchers also collected additional samples from other areas across the southeastern US whenever possible.
Most snakes were captured alive so scientists could swab their skin and collect blood samples before release. A smaller number of snakes that had died on roads or in the wild underwent detailed postmortem examinations that included tissue collection.
“For around 10 years, free-ranging snake research almost solely focused on Oo. We wanted to evaluate snake health on a more comprehensive level and really establish a broader view,” Mishin said.
Multiple Infections Common in Wild Snakes
The researchers discovered that fewer than 20% of the snakes tested showed no signs of infection.
The most widespread pathogen was the bacterium Salmonella enterica, which appeared in 63% of the snakes. Another common infection came from Hepatozoon spp., a tick borne parasite found in 53% of the animals.
Scientists also detected antibiotic resistant Mycoplasma spp. bacteria in 18% of snakes. These bacteria can cause upper respiratory illness and had never before been reported in wild snakes in the United States.
Many snakes were carrying more than one pathogen at the same time. Overall, 44% of the snakes had multiple infections. About 29% carried two pathogens simultaneously, while 11% had three infections and 3% carried four different pathogens.
“When an animal has become sick from an infection their immune system is compromised which increases the risk of further disease exacerbation from other infectious agents that may have once been subclinical,” Mishin explained.
Pygmy Rattlesnakes Face Elevated Risk
The study also found that some snake species were much more vulnerable to certain diseases than others.
Pygmy rattlesnakes showed especially high rates of snake fungal disease. Of the 34 rattlesnakes tested, 12 were positive for Oo, and many also displayed visible signs of illness. By comparison, only one out of 55 eastern ribbon snakes and three out of 36 ring necked snakes tested positive.
Rattlesnakes were also the species most frequently infected with Ro, an invasive crustacean parasite commonly known as snake lungworm. Fourteen of the 34 rattlesnakes carried the parasite. In several other snake species, Ro infections were much less common or absent altogether, including among Florida green watersnakes.
“We hypothesize that certain species with poorer general population health, specifically rattlesnakes with historic and current increased risks of human persecution, are likely more susceptible to infection with subsequent disease,” said Mishin. “In addition, pygmy rattlesnakes were expected to have an increased prevalence of Ro, as they primarily consume lizards and frogs which are known to transmit the parasite.”
Geography and Skin Damage Influence Infection Risk
Location also appeared to affect infection patterns. Snakes sampled in Georgia were much more likely to test positive for Oo, while Ro infections were found only in Florida snakes.
Skin damage was another important factor. More than 30% of snakes with skin lesions tested positive for snake fungal disease, compared to just 2% of snakes without lesions.
Disease Risks and Conservation Concerns
The researchers noted several limitations to the study. Sampling took place in only a small number of counties, meaning the findings may reflect local environmental conditions rather than the entire southeastern US.
The team also explained that detecting Ro in living snakes can be difficult because testing relies on fecal samples. Since snakes often go long periods without eating, usable samples are not always available. As a result, the true rate of Ro infection may be higher than reported.
Even so, the researchers say the findings could play an important role in wildlife conservation and invasive species management. Burmese pythons and brown anoles, both invasive species in the US, are known carriers of Ro.
“Our data provide important information of which pathogens native snakes may likely have but also which they are likely naïve to. This can inform actions needed to prevent pathogen spillover from captive snakes,” Mishin concluded. “When translocating wildlife, it’s essential to consider which pathogens may be translocated with them — and the potential downstream effects.”