A “sauna” treatment for frogs has been used by researchers in Australia to successfully fight a deadly fungal disease that has devastated amphibians around the world, according to a new study.
Scientists created refuges for the animals using painted bricks in greenhouses they called “frog saunas”. They found that endangered Australian green and golden bell frogs were able to clear infections of the deadly Batrachochytrium dendrobatidis fungus, in the warmer conditions of the greenhouses, when they would otherwise have died. Many of the frogs that recovered in the refuges were then resistant to infection.
While the technique has previously been unsuccessful for other frog species, researchers found that the green and gold bell frog – once common in south-eastern Australia – responded well to the treatment, a discovery that offers hope for their future survival. Researchers said the rare amphibians were selected after careful testing, which found they preferred the bricks as a habitat.
“Why are we so excited about [the study’] there is just nothing that works [to stop the infection],” said Dr Anthony Waddle, a postdoctoral researcher at Macquarie University in Sydney, who led the study. “The last line of defense is to bring the frogs into captivity where you can heal and protect them. We are slowly seeing how species look out.”
In glacial ponds and alpine lakes, rainforests and wetlands, the deadly fungus has killed off the word’s amphibian populations. By at least 90 species are known to have become extinct and many more are expected to disappear in the coming years. Scientists say this is the largest recorded loss of biodiversity attributable to a single disease.
The Tanzanian Kihansi toad, Honduran Cerro Búfalo toad and Mexican clawed salamander are among the species thought to have been wiped out in the wild by the infection.
Waddle said that while there are caveats about where the steam room strategy could be used, it was a rare piece of good news for the green and gold bell frogs. “This species is really restricted to the coastal area of its former range. Ninety percent of its populations have gone and more and more go every year. They are not doing well. They don’t come back. They do not show that clear sign of recovery that some other species have done on their own. So we’re excited,” he said.
The fungus, which is often known as Bd, causes a disease called chytridiomycosis in amphibians. It was formal identified by researchers in 1998 after widespread frog die-offs around the world. The infection attacks the amphibians’ skin, causing heart attacks and death. The deadliest strain of the disease appears to be about 100 years old and researchers think it was probably spread by humans.
Andrew Cunningham, the professor of wildlife epidemiology at the Zoological Society of London’s Institute of Zoology who the fungal disease first identifiedsaid the technique had been tried with other species, but there was no evidence it worked for them.
“We did this by manipulating their natural environment to increase sun exposure and soil and water temperature, and by installing heated ponds (to a temperature above which the fungus cannot survive, but the frogs can). We still had fatal outbreaks of chytridiomycosis and the only way to stop it was to bring the frogs under human care to treat them with a fungicide,” he said.
“Perhaps the technique is species-specific, but unfortunately I doubt it is a silver bullet to tackle the global threat of amphibian chytridiomycosis,” he added.
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