‘Frog Saunas’ May Be the Key to Saving Amphibians From a Deadly Fungal Infection

Providing frogs with sun-warmed bricks inside mini-greenhouses can help them recover from chytrid and make them more resilient against the disease in the future, a new study finds

Frogs sticking heads out of brick holes next to green foliage
The frog saunas are easy to make and cost around $50 to put together. Anthony Waddle

A deadly fungal disease known as chytrid has been killing salamanders, frogs and toads around the world. For years, conservationists and scientists have fought to protect amphibians as chytrid decimated their populations, leading to the extinctions of at least 90 species.

Now, however, researchers say they’ve come up with a novel treatment for the disease: frog saunas.

Frogs with access to warm shelters have an easier time fending off the fungus, scientists reported Wednesday in the journal Nature. And those that overcame the disease with help from a bit of heat were also more resilient against repeat infections in the future.

“It’s a superinnovative and impressive paper,” says Brian Gratwicke, a conservation biologist at the Smithsonian’s National Zoo and Conservation Biology Institute who was not involved with the research, to Science’s Erik Stokstad. “The implications are very hopeful.”

Frog sitting on top of a brick
The study focused on green and golden bell frogs, which live in southeastern Australia. Anthony Waddle

Chytrid is short for chytridiomycosis, a fatal disease that can cause amphibians to become lethargic and stop eating. They may also excessively shed their skin, suffer convulsions and become disoriented, as the infection ultimately leads to cardiac arrest.

Chytrid is caused by the fungus Batrachochytrium dendrobatidis, or Bd for short. As it turns out, Bd thrives in cool weather but does not fare well when exposed to higher temperatures. This downfall got scientists thinking: What if people could create warm places for frogs to hang out when the temperature drops?

For the new study, researchers focused on the green and golden bell frog (Litoria aurea), a species that lives in southeastern Australia and has been severely affected by chytrid. In one experiment, they placed infected frogs in enclosures with a temperature gradient. The frogs hopped toward regions that were an average of 84 degrees Fahrenheit, which is too hot for Bd to survive.

Once the researchers demonstrated that frogs gravitate toward warmer areas, they set up a second experiment that involved placing infected frogs in enclosures set to various temperatures. Infected frogs that lived in cooler habitats—with temperatures around 66 degrees Fahrenheit—had higher levels of fungus on their skin and were more likely to die in the ensuing months.

But infected frogs kept in warmer enclosures were able to fend off their infections and recover. Additionally, when frogs could choose the temperature of their surroundings, they successfully cleared their infections even more quickly.

“This is really exciting,” says study co-author Anthony Waddle, a biologist at Macquarie University in Australia, to CBC News’ Anand Ram. “If frogs are given the opportunity, they can [help] themselves.”

Green frogs poking their heads out from holes in bricks
Researchers capitalized on the frogs' natural tendency to hang out in brick holes. Anthony Waddle

In a third experiment, researchers placed bricks with holes in them in large outdoor enclosures. (They’d previously observed that frogs love to hunker down in brick cavities.) They topped the bricks with small greenhouses made from plastic tarps, half of which were exposed to the sun and half of which were kept in the shade.

They put a mix of healthy, sick and previously infected frogs into the enclosures. The creatures flocked to the greenhouse-covered bricks, whether they were shaded or sunny. But compared to frogs resting in the shade, frogs in the sunny enclosures had body temperatures that were around 6 degrees Fahrenheit higher. This difference was enough to help kill off the fungus—sometimes, infections were 100 times worse for frogs in the shaded enclosures.

“Just a few degrees difference can tip the scales for the frogs,” Waddle tells the New York Times’ Emily Anthes.

Little green tents sitting on the ground outside
Frogs in the sunny enclosures had body temperatures that were around 6 degrees higher than those in the shady enclosures. Anthony Waddle

The frogs that had already overcome Bd with help from a previous heat treatment also fared better against the fungus, regardless of whether they were in the sunny or shady condition. This suggests the makeshift saunas can supercharge frogs’ immune systems.

“Using the shelters and surviving is like a vaccination for the frogs,” Waddle tells New Scientist’s James Woodford. “We have shown that the bell frogs can gain resistance after an infection is cured with heat, and this can lead to a 22 times greater chance of surviving a future infection, even under cold conditions.”

Frog saunas won’t work for all species. But they may be a promising path forward for some creatures that can tolerate, and even seek out, heat. Already, researchers are placing frog saunas in some public areas, including Sydney Olympic Park, which has a population of green and golden bell frogs. They’re also putting out a call to action and encouraging residents to build frog saunas on their properties—a craft project that costs about $50. The team has even put together a handy guide to building your own frog sauna at home.

“The beauty of this experiment is that it could be [widely deployed],” says Ana Longo, a biologist at the University of Florida who was not involved with the study, to Popular Science’s Lauren Leffer. “Many species might possibly benefit from this. It’s very cheap to do, and easy. This could be easily implemented by wildlife managers and conservation agencies.”

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