Graduate student studies how snake fungal disease could spread

By Meghan Chua


Snake fungal disease is considered an emerging infectious disease. It causes swelling, scabs, ulcers, and crusty or discolored scales on affected snakes. With mild cases, snakes can shed their skin and rid themselves of the infection. But in severe cases, the snake’s face becomes swollen or disfigured, affecting its ability to eat and leaving it emaciated and weak.

A corn snake
Snake fungal disease affects many different snake species across the U.S. PhD student Savannah Gentry used corn snakes like the one pictured here and another reptile, bearded dragons, to test whether the pathogen that causes snake fungal disease could infect other hosts.

Scientists study snake fungal disease because of snakes’ importance as both a predator and prey. Snakes eat rodents that damage crops and small mammals that can carry Lyme-disease ridden ticks. Snake populations have been declining worldwide, leading to concern about what will happen to them now and in the future, said Jeffrey Lorch, a microbiologist at the U.S. Geological Survey National Wildlife Health Center in Madison.

“In Wisconsin, habitat fragmentation plays a big role. Snakes aren’t like birds; it’s not easy for them to move from one chunk of habitat to another,” said Lorch, who earned a PhD in Molecular and Environmental Toxicology from UW–Madison in 2012. Collectors finding wild snakes to trade as pets and climate change may also cause declining populations in the area.

Snake fungal disease began to gain attention about a decade ago, Lorch said. Unlike invasive fungal pathogens like that which causes white-nose syndrome in bats, Lorch said the evidence suggests Ophidiomyces ophiodiicola, the fungus that causes snake fungal disease, has been around in the U.S. for a while.

While scientists have studied infected snakes’ behavior and the symptoms of snake fungal disease, few studies looked at whether O. ophiodiicola could spread to other species. That was the central question for Savannah Gentry, a botany PhD student in Anne Pringle’s lab, who wanted to find out whether snake fungal disease could affect other reptiles.

To test this, Gentry chose bearded dragons and a fungus that has been found on them called Nannizziopsis guarroi. N. guarroi is similar to O. ophiodiicola in causing skin infections in its host, possibly by degrading the keratin that composes skin and scales. Gentry inoculated corn snakes with N. guarroi and the bearded dragons with O. ophiodiicola to see if they could infect a new host.

Savannah Gentry
PhD student Savannah Gentry with skin samples from snakes in her experiment on whether the fungal pathogen that causes snake fungal disease could spread to another reptile.

“We could see that at least both of these fungi were capable of infecting different hosts, which has a lot of other implications about where they are in nature and if they’re infecting lizards,” Gentry said. The study also confirmed that N. guarroi, the fungus found on bearded dragons, does in fact cause infections in bearded dragons.

Gentry’s results are important for places such as pet stores and private homes, where different species who wouldn’t encounter one another in the wild are brought together.

“The ability of these fungi to start moving around and jumping hosts in captivity, and then the potential for those to spill back into the wild, is a valid concern,” Lorch said.

Snake fungal disease has been found to be widespread across the country. Since her study with corn snakes and bearded dragons, Gentry has worked with the U.S. Geological Survey in Louisiana as a snake catcher, surveying for snake fungal disease and learning more about what it looks like in the wild. Along with USGS researchers, Gentry waded into a swamp in Louisiana and circled the area looking for snakes. Each time they caught one, the researchers logged the snake’s weight and any sign of snake fungal disease, and often swabbed to test for the fungus.

“Wild snakes have tons of scrapes and bruises and bumps, so without swabbing the snake it can be really difficult to see exactly what snake fungal disease is on a wild snake unless the symptoms are so severe,” Gentry said. In Wisconsin, most of the cases aren’t particularly severe, which makes it challenging to tell whether a snake here is infected by sight alone.

That the fungus causing snake fungal disease can live on other reptiles doesn’t necessarily mean it will cause infection in that host. Even among snakes, some species exhibit more severe symptoms from snake fungal disease than others. Gentry plans to study enzymes in her next project to determine how their expression in fungi may affect the presence and severity of a fungal infection.

“On a very basic level, it’s asking the question, why does this work the way it works?” Gentry said. “It’s trying to unpack what is the point in which something that is naturally a part of our ecosystem – that degrades leaf litter or carcasses in the wild – at what point does that become a pathogen?”