Survival of Endangered Frogs Boosted by Winter Sauna Treatment for Fungal Disease

One of Australia’s most endangered amphibians can fight off a deadly fungal infection with the help of a naturally heated shelter that researchers are calling a “frog sauna.”

The disease, chytridiomycosis, has wiped out about 100 species of frogs, toads and salamanders worldwide.

Green and gold bell frog (Litoria aureaThe fungus was once widespread along the south-eastern coast of Australia, but its range has shrunk by 90 percent, and although other factors such as habitat loss are also at play, chytrid is thought to be the greatest threat to the endangered species.

It has long been known that warm temperatures suppress fungal infections, and many frog species, including the Japanese bush frog, are susceptible to the disease in winter when it’s hard for them to stay warm, especially when it’s hard to find a warm place.

To learn more, Anthony Waddle The researcher, from Macquarie University in Sydney, and his colleagues studied two groups of captive frogs that were intentionally infected with chytridiomycosis over the winter.

The first group was provided with bricks with holes in them in an unshaded greenhouse shelter where temperatures rose to nearly 40°C (104°F), while the second group was provided with bricks in a shaded greenhouse shelter where temperatures rose to 35°C (95°F).

Frogs that were given warmer shelter had 100 times fewer chytrid spores on their skin than other groups.

Although chytrid has difficulty growing above 28°C (82°F), warmer temperatures appear to activate the frogs’ immune systems, Waddle said.

“Using shelter to survive is like a vaccination for the frogs,” Waddle says, “and we’ve shown that firefly frogs can develop resistance after heat has cleared their infection, potentially making them 22 times more likely to survive future infections in cold environments.”

Although the researchers have only tested the shelter on one species at this stage, they believe the technology could be used with other animals threatened by chytrid fungus, as long as they seek out natural warmth when it’s cold. Waddle says there are at least six Australian animal species that could benefit from the technology.

Importantly, these thermal shelters are easy and inexpensive to set up: “All you need is a small vegetable greenhouse from the hardware store and a few bricks, and it will only cost about $60-70. [Australian] “It will cost a few hundred dollars to build,” Waddle said, “and I can envision people putting them in their backyards to help the frogs through the winter.”