To put a disease that’s ravaging ecosystems around the world into context, biologist Roland Knapp describes it like COVID-19 — if COVID-19 had a 99 per cent mortality rate.
“If we can imagine that, we can get a sense of what the impact is on amphibians,” says Knapp, a research biologist at the Sierra Nevada Aquatic Research Laboratory out of the University of California, Santa Barbara.
Chytridiomycosis — or chytrid (pronounced KITT-ridd) — is a fungal skin disease that can lead to heart failure. Having wiped out at least 90 species of frogs, chytrid has been called the most devastating infectious disease for wild animals in recorded history.
Solutions, few and far between, range from airlifting species to distant zoos for breeding, to building DIY brick saunas.
But a new long-term study, recently published in Nature Communications by Knapp and his team, provides hope — and experts say their findings have the potential to help bring other species back from the brink.
New research has found that spa-like bunkhouses can help protect frogs from the deadly chytrid fungus. They’re made from common materials and when heated by the sun turn into saunas that can help frogs recover from the infection and become resistant to future outbreaks.
Learning from survivors
In the majesty of California’s Yosemite National Park, the sounds of the mountain yellow-legged frog used to fill the air.
“When we look at historical references, old notebooks, some of the notes talk about how any day that you spent walking along lakes and streams, you would see hundreds of these frogs,” Knapp said
Over the decades, that sound was stolen — first by a combination of non-native fish, then by chytrid. Normally, a chytrid outbreak is game over — but some populations survived the devastation, and Knapp’s research focused on them.
“We looked at the [survivors’] chytrid loads, the degree to which those frogs are infected with the chytrid fungus,” Knapp said. “They were infected at much lower levels than they had been when the fungus first arrived.”
In other words, these survivors showed signs of resistance or tolerance to the disease. But a big question remained: Was this caused by a characteristic of the frog, or by an outside factor?
Amphibian airlift
More testing gave the team confidence that the resistance came from the frogs themselves. They put survivors in the same tank as “naive” frogs — those that had never dealt with chytrid — and found the naive population did much worse against the disease.
The final test would be seeing if resistant frogs could survive in the wild if they were introduced to new areas.
That required helicopters.
Knapp’s team spent years relocating the frogs to lakes at high elevations in the Sierra Nevada mountains.
After 15 years of work — including painstaking capture-mark-recapture surveys, where adult frogs are caught and tagged to measure progress — the results were positive: Most of these yellow-legged frogs were surviving and reproducing healthy offspring.
This meant they passed on qualities of resistance that helped their young survive into adulthood against the fungus, which was still very present in their environment.
“They are thriving now in the presence of this pathogen that, a generation or two generations of frogs previously, … wiped them out,” Knapp told CBC News.
Findings spark hope
Experts not involved with the research see hope in this method, but are cautious given the scale of chytrid’s reach.
“This is a very rare study,” says Ana Longo, an amphibian disease expert at the University of Florida. She says the detailed and long-term data is very positive, at least in the case of this one species.
“But then … I think about what’s going to happen in the tropics, [where] we have hundreds of species living together,” Longo told CBC News from Gainesville, Fla.
Chytrid is present on every continent but Antarctica, but research has shown it has a particularly lethal impact in South and Central America, leading to severe declines and extinctions of many species.
“I think that’s when things get a little bit challenging,” Longo said. “But the idea is that it’s possible.”
Vital role in ecosystems
María Forzán, wildlife pathologist with the University of Wyoming, calls the results promising. She says this resistance in frogs was long suspected, but it was good to see it tested in this way.
However, she warns that longer-term studies are needed to better understand how this resistance works — and that may take time and money that such studies don’t always get.
There also needs to be a “coherent and executable policy approach to wildlife disease,” she added, because threats to these creatures don’t just come from pathogens, but from human development and trade, too.
For Knapp, long-term conservation efforts for these frogs are important, given they support ecosystems in their dual lives as both aquatic and terrestrial creatures. Returning them to their habitats and letting them naturally recover brings more than their sounds back to Yosemite National Park.
“You see the bears come back, you see the garter snakes come back, the coyotes come back,” Knapp said. “It’s a pretty remarkable transition, but it takes a long time to see it happen.”