A fungal infection that some scientists call one of the worst wildlife diseases of all time is wreaking havoc on the world’s frog population. Now scientists say they’ve discovered a way to help frogs fight back: tiny saunas.
Dozens of frogs placed inside hollow black bricks in Australia were doing more than just soaking up the sun’s heat in the winter of 2021. Inside the roughly 100-degree boxes built to mimic the saunas found at spas, the frogs were battling chytridiomycosis, a fungal infection that causes their skin to grow up to 40 times thicker than normal.
The heat cured the infection within a few weeks, and about 70 percent of the infected frogs survived the 15-week experiment, said lead researcher Anthony Waddle. Waddle and a team of biologists published the results last week in Nature magazine, hoping that his simple invention will help solve a huge wildlife problem.
Waddle built the shelters using black bricks and greenhouse netting.
“It’s going to be freezing cold outside, but as soon as you walk in … you’re going to be sweating profusely because of the humidity and the heat,” Waddle, a postdoctoral researcher at Macquarie University in Macquarie Park, Australia, told The Washington Post.
Chytridiomycosis, which originates from Batrachochytrium dendrobatidisThe waterborne fungus is thought to have first been found in Asia in the 1930s, before trade and travel caused it to spread rapidly around the world. The contagious fungus, which has driven dozens of amphibian species to the brink of extinction, causes breathing problems until many amphibians’ hearts stop.
Scientists have attempted to protect amphibians by removing infected species from their habitats, chemically disinfecting their homes, and heating their water sources to combat the fungus. In 2021, Waddle created a vaccine for frogs against Batrachochytrium dendrobatidisHowever, he wanted to invent a solution that frogs could use themselves, especially in the winter when cases of chytridiomycosis are highest.
In December 2020, Waddle placed some green and golden bell frogs, which are endangered in the Australian state of New South Wales, near a metal fence post, which was cold on one side and warm on the other. The frogs leaned toward the warm side.
The researchers then divided 66 infected frogs between warm and cool areas in their lab. The frogs in the warm area, which was about 86 degrees, fought off the infection, while those in the cool area, which was about 66 degrees, remained infected.
These results led researchers to believe that frogs would choose to live in a warm habitat (and benefit from it) if researchers created one.
The scientists used their building materials for the main experiment: clay bricks, black paint, greenhouse netting and zip ties. They painted the bricks black to attract the sun’s heat. Then they stacked 10 bricks, each with 10 small holes, on top of each other. They covered several stacks of bricks with greenhouse netting to retain heat, and zip ties stabilized the shelters.
“I didn’t think it would work because of its simplicity,” Waddle said.
At Macquarie University’s campus in July 2021, researchers placed shelters in tubs filled with gravel, water, artificial plants and pots to mimic typical frog habitats. 239 frogs were then placed in the tubs and given a choice between an unshaded shelter or a shelter with fabric shade. Most opted for the warmth of the bricks in the unshaded shelters.
The unshaded shelters were about eight degrees warmer than the shaded habitats, and that made a difference. About a month into the experiment, the researchers took skin samples from the frogs and found that the infection healed more quickly in the frogs living in the unshaded shelters.
In November 2021, just before the Australian summer began, 167 of the 239 frogs were still alive, Waddle said. Wild frogs typically begin to die about three weeks after becoming infected, according to the Ohio Department of Natural Resources.
The researchers also found that frogs that survived chytridiomycosis became more resistant to the disease, a promising sign for the survival of the species, which can live about 15 years in captivity.
Bryan Pijanowski, a professor of forestry and natural resources at Purdue University, said in an email to The Post that the shelters Waddle built offer a “bit of optimism” for solving a disease that has wiped out at least 90 amphibian species.
“These are alarming figures that require innovative approaches to turn the tide,” he said.
Waddle has installed some shelters at Sydney Olympic Park, Australia, home to one of the largest remaining populations of green and golden bell frogs. He plans to monitor the population over the next few years.
He said that he He hopes parks and homeowners will implement their own “frog saunas.” He created a public guide for building them, estimating that each one costs about $80.
“Conservation research is a huge loss,” Waddle said. “You just try things, they don’t work. You try things, they don’t work. But we have something, and it’s something we can offer right away.”
