A yellow-legged frog returns to the wild in the Desolation Wilderness, south of Lake Tahoe.

A yellow-legged frog returns to the wild in the Desolation Wilderness, south of Lake Tahoe. (Josh Cassidy/KQED)

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A deadly fungus that’s been devastating frog populations is still spreading across the globe. In California, the chytrid fungus has moved inexorably across the Sierra Nevada from west to east, leaving thousands of frogs dead.

But Bay Area scientists are trying to turn the tide against the fungus with an experimental treatment, one that could matter to frogs worldwide.

They’re making a last-ditch effort to save the endangered mountain yellow-legged frog by immunizing it against chytrid.

Mountain yellow-legged frogs, found only in California’s alpine lakes, have been in steep decline due to the fungus as well as predation by non-native trout. More than 90 percent of the population has disappeared.

Video produced by Gabriela Quirós.

“When it hits, it’s within weeks that they’re just gone, just literally gone,” says Jessie Bushell, director of conservation at the San Francisco Zoo.

Bushell is part of an emergency search-and-rescue operation for the frogs.  Like last summer, when she got up before dawn and drove five hours to meet a helicopter flying out of the Sierra Nevada.

“This bright yellow helicopter comes landing down,” she says. “The doors fly open. The firefighters start unloading these large white coolers.”

The coolers were holding hundreds of wiggling, green tadpoles, the sole survivors of a deadly outbreak at their remote alpine lake. Federal biologists had found dozens of frogs dying from chytrid fungus and, hoping to save the species, had collected their remaining young.

Priming Immunity

Bushell brought them to the San Francisco Zoo. Scientists there and at the Oakland Zoo are doing an experimental treatment on the frogs in the hope that they’ll survive when they return to the wild. The treatment was pioneered at UC Santa Barbara, where results have been encouraging.

“So what we do is we expose them to small amounts of this fungus,” Bushell says, pointing to more than 200 of the frogs, no longer tadpoles, in quarantined tanks.

Bushell is making the frogs sick in the hope of building their immunity to chytrid fungus, which attacks the frog’s skin.

Mountain yellow-legged frogs get an experimental vaccination at the San Francisco Zoo.
Mountain yellow-legged frogs get an experimental vaccination at the San Francisco Zoo. (Josh Cassidy/KQED)

“The skin is a really important part of the frog,” she says. “They breathe through their skin underwater.”

Frogs also absorb key nutrients such as electrolytes through their skin. But when the fungus attacks it, the skin stops functioning normally. The frogs die before their immune systems can fight the fungus off.

Bushell is hoping a mild fungal infection will teach the frogs’ immune systems how to fight chytrid. She lets her frogs get sick, but before they get too close to dying, she gives them an anti-fungal treatment to clear up the infection.

When the frogs get chytrid again out in the wild, the idea is their immune systems will be trained.

Roland Knapp releases a yellow-legged frog in a high alpine lake, south of Lake Tahoe.
Roland Knapp releases a yellow-legged frog in a high alpine lake south of Lake Tahoe. (Lauren Sommer/KQED)

“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,” she says.

Back to the Wild

For some of the yellow-legged frogs, the big test has arrived. Bushell and a field crew hike up a rocky trail in the Desolation Wilderness, south of Lake Tahoe.

Their big backpacks are loaded with frogs, each in its own tiny Tupperware container.

“It’s a new frog home,” says Bushell, looking at a sapphire-blue lake, surrounded by pine trees and granite cliffs. “An oasis for frogs.”

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But chytrid fungus is there, so their immunity will be tested. One-by-one, the team releases each frog on the water’s edge.

“It’s like letting your kids go,” says Bushell. “Go! Be wild!”

“It’s the best chance that we know how to give them,” says Roland Knapp, a biologist with UC Santa Barbara who has tracked frog die-offs across the Sierra as the chytrid wave has moved through.

“I saw the biggest one I’ve ever seen last summer,” he says. “Thousands of dying frogs. Carcasses of frogs all over the place. It was pretty rough to see.”

That threat is why biologists are going to such lengths to save yellow-legged frogs.

Mountain yellow-legged frog populations have declined by more than 90 percent.
Mountain yellow-legged frog populations have declined by more than 90 percent. (Lauren Sommer/KQED)

“It sometimes seems a little crazy,” Knapp says. “It’s a huge amount of work.”

But he says the early results are promising. This is the third summer the team has released vaccinated frogs.

“They seem to be surviving pretty well,” he says.

If the immunized frogs survive the worst of the fungus outbreak, the mountain yellow-legged frogs may eventually be able to become resistant to it on their own, generation-after-generation, without human help.

“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 says.

Jessie Bushell with a treated frog at the San Francisco Zoo.
Jessie Bushell with a treated frog at the San Francisco Zoo. (Lauren Sommer/KQED)

The biggest hope, and the biggest question mark, is whether this research could lead to a treatment for other frog species. Some frogs don’t seem to be able to build immunity to chytrid like the yellow-legged frogs can.

Scientists have watched chytrid fungus spread across the globe at an alarming rate, driving 200 frog species to extinction. In Central America, scientists have brought some frog species into captivity to spare them.

Today, that’s the only place they exist. And they don’t have much hope of going back to the wild unless some kind of chytrid treatment succeeds.

“We’re staring at what could be the extinction of a significant fraction of the world’s amphibians,” Knapp says. “So if we can do something to reverse that, even for a few species here and there, we should try to do that.”

It’s not hopeless, scientists say, but it could depend in large part on the survival of one California frog.

Can a New ‘Vaccine’ Stem the Frog Apocalypse? 27 September,2016Lauren Sommer
  • ericmills

    The chytrid problem is exacerbated by the fact that California annually imports some TWO MILLION non-native bullfrogs for human consumption, commonly sold in the state’s many live food markets in various “Chinatowns” in Oakland, San Francisco, Sacramento, San Jose, Los Angeles and elsewhere. Recent studies have documented that the majority of the bullfrogs (most are commercially-raised) test positive for the chytrid fungus.

    The market frogs are routinely bought live from the markets and released into local waters by “do-gooders,” certain religious sects for “animal liberation” ceremonies, and others. The exotics prey upon and displace the natives, while spreading diseases.

    Adding to the problem is the annual Frog Jump in Calaveras County. Non-native American bullfrogs, with the blessing of the Dept. of Fish & Wildlife, have taken the place of Mark Twain’s red-legged frogs. These “jumps” need to cease. The DFW requisitioned a “White Paper” on the bullfrog problem back in 2014 from UC Davis. The Summary of the paper suggested a total import ban as the best solution, yet the Dept. has failed to act, and our resources continue to suffer accordingly. Twenty years & counting….

    WRITE: Chuck Bonham, Director, Dept. of Fish & Wildlife, Resources Building, 1416 Ninth Street, Sacramento, CA 95814; email – director@wildlife.ca.gov. With a cc to John Laird, Secretary of Resources, same address, email – secretary@resources.ca.gov

    Eric Mills, coordinator

  • KimberlyAyers

    Hi Lauren, so what impact does the frog decline have on their ecosystem? insect overpopulation? I know when you remove one part of a system it throws the rest out of balance. Is California doing anything about the non-native trout? Purely selfish, I know, but I love the sound of frogs at night when I’m camping! — thanks.

  • mikekingman

    http://www.end-times-prophecy.org/animal-deaths-birds-fish-end-times.html Zephaniah 1 (KJV)
    2 I will utterly consume all things from off the land, saith the Lord.

    3 I will consume man and beast; I will consume the fowls of the heaven, and the fishes of the sea, and the stumbling blocks with the wicked: and I will cut off man from off the land, saith the Lord.?

    Hosea 4 (KJV)
    4 Hear the word of the Lord, ye children of Israel: for the Lord hath a controversy with the inhabitants of the land, because there is no truth, nor mercy, nor knowledge of God in the land.

    2 By swearing, and lying, and killing, and stealing, and committing adultery, they break out, and blood toucheth blood.

    3 Therefore shall the land mourn, and every one that dwelleth therein shall languish, with the beasts of the field, and with the fowls of heaven; yea, the fishes of the sea also shall be taken away.? Our Heavenly Fathers will,will be done naturally,manmade,or unexplained. It’s all over the world! here is just a few MASS ANIMAL DEATH LIST 427 Known MASS Death Events in 75 Countries (or Territory)

    16th September 2016 – TONS of dead sardines washing up on a beach in Jeddah, Saudi Arabia. Link

    15th September 2016 – 500 dead Horseshoe crabs have ‘mysteriously’ washed up in Kitakyushu, Japan. Link

    15th September 2016 – Thousands of dead fish found along a river in Paradip, India. Link

    14th September 2016 – 700+ storks die in a storm in Majuli, India. Link

    13th September 2016 – Dozens of sea birds found dead along beaches in the Gulf Coast, America. Link

    12th September 2016 – 140 dead turtles found washed up this year, ’cause unknown’ in Baja California, Mexico. Link

    12th September 2016 – 2,500 cattle dead due to drought in Machareti, Bolivia. Link

    11th September 2016 – Millions of fish have suddenly died in fish farms in Beihai City, China. Link

    11th September 2016 – Thousands of dead fish found in Snake River in Idaho, America. Link

    10th September 2016 – Massive amount of dead fish found along a river in Fujian, China. Link

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Lauren Sommer

Lauren is a radio reporter covering environment, water, and energy for KQED Science. As part of her day job, she has scaled Sierra Nevada peaks, run from charging elephant seals, and desperately tried to get her sea legs - all in pursuit of good radio. Her work has appeared on Marketplace, Living on Earth, Science Friday and NPR's Morning Edition and All Things Considered. You can find her on Twitter at @lesommer.