(CN) — A deadly fungus that's driven 200 species of frogs to extinction has spread across the Sierra Nevada, and scientists believe an experimental vaccine may be the only hope for the endangered mountain yellow-legged frog.
The chytrid fungus has already killed thousands of frogs in the mountain range, and appears to be growing at a rate that might be impossible to stop.
But despite the danger posed by the fungus, scientists believe they can turn the tide with an experimental treatment that could help frogs worldwide.
A team of researchers has immunized the mountain yellow-legged frogs against the fungus. The species is found only in California's alpine lakes, and has been in steep decline due to the fungus and non-native trout. More than 90 percent of the species has disappeared.
"When it hits, it's within weeks that they're just gone, just literally gone," Jessie Bushell, director of conservation at the San Francisco Zoo, told the Southern California radio station KPCC.
Bushell is a part of an emergency search-and-rescue operation for the endangered frogs. Last summer, Bushell and other team members woke up before dawn and drove five hours to meet a helicopter flying out of the Sierra Nevada.
Upon arriving at the site, firefighters popped out of the helicopter carrying large white coolers that contained hundreds of wiggling, green tadpoles — the only survivors of the chytrid fungus outbreak at their remote alpine lake.
After previously finding dozens of frogs dying from the fungus, federal biologists decided to round up their remaining young. Bushell brought them to the San Francisco Zoo, where scientists there and at the Oakland Zoo performed an experimental treatment on the frogs in the hope that they'll survive when they return to their natural habitats.
"So what we do is we expose them to small amounts of this fungus," Bushell said.
The team is making the frogs sick in order to build their immunity to the fungus, which attacks the frogs' skin.
"The skin is a really important part of the frog," she said. "They breathe through their skin underwater."
Besides breathing, frogs also use their skin to absorb key nutrients such as electrolytes. However, when the fungus attacks it, the skin no long functions normally and the frogs die before their immune systems can fight off the fungus.
The team is hoping that a mild fungal infection will teach the frogs' immune systems how to fight the fungus.
"Their bodies identify it and can already be primed to fight off that infection, at least to keep it under control because they've seen it before," Bushell said.
Some of the mountain yellow-legged frogs were recently returned to the wild by Bushell and a field crew, leaving them in an area south of Lake Tahoe.
"It's a new frog home," said Bushell, referring to the sapphire-blue lake. "An oasis for frogs."
Ronald Knapp, a biologist with the University of California, Santa Barbara, who has studied frog die-offs across the Sierra Nevada as the chytrid wave swept through the area, told KPCC that the team's attempt to immunize the frogs against the fungus is the best option remaining.
"It's the best chance that we know how to give them," he said. "It sometimes seems a little crazy. It's a huge amount of work."
Knapp said the early results are encouraging.
This is the third summer the team has released immunized frogs.
If the frogs can survive the worst of the fungus outbreak, they may eventually be able to become more resistant on their own, generation after generation.
"That means we have to figure out ways to keep these frogs on the landscape with the chytrid long enough that evolution can actually happen," Knapp said.
The team hopes the research can be applied toward a treatment for other frog species, but only time will tell: Some species of frogs don't seem to be able to build immunity to chytrid.
The fungus has spread quickly across the globe, forcing scientists to bring some frog species into captivity to avoid extinction.
"We're staring at what could be the extinction of a significant fraction of the world's amphibians," Knapp said. "So if we can do something to reverse that, even for a few species here and there, should try to do that."
The survival of the mountain yellow-legged frog could play a significant role in reversing this trend.
Follow @SeanDuffyCNS
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