Since the 1970s, the aquatic fungus Batrachochytrium dendrobatidis has triggered die-offs in hundreds of amphibian species such as the common midwife toad (Alytes obstetricans). These frogs—arranged in rows by researchers documenting the fungus—died in the French Pyrenees.
PHOTOGRAPH BY MATTHEW FISHER
Many of the world’s amphibians are staring down an existential threat: an ancient skin-eating fungus that can wipe out entire forests’ worth of frogs in a flash.
This ecological super-villain, the chytrid fungus Batrachochytrium dendrobatidis, has driven more than 200 amphibian species to extinction or near-extinction—radically rewiring ecosystems all over Earth.
“This is the worst pathogen in the history of the world, as far as we can tell, in terms of its impacts on biodiversity,” says Mat Fisher, an Imperial College London mycologist who studies the fungus.
Now, a global team of 58 researchers has uncovered the creature’s origin story. A groundbreaking study published in Science on Thursday reveals where and when the fungus most likely emerged: the Korean peninsula, sometime during the 1950s.
From there, scientists theorize that human activities inadvertently spread it far and wide—leading to amphibian die-offs across the Americas, Africa, Europe, and Australia.
“[The pathogen’s spread] could have happened from any one event, from the cumulative number of events, or maybe some big anthropogenic events like the Korean War,” says Imperial College London researcher Simon O’Hanlon, the study’s lead author.
Now that researchers know where the fungus came from, they can monitor this hotspot of chytrid diversity for new, deadly species. The findings also serve as a stark reminder that if left unsecured, global trade can unwittingly fuel ecological catastrophes.
The fungus—called Bd for short—is so deadly because it targets amphibians’ porous skin, which the animals use to breathe and drink water. Bd unspools the skin’s proteins and feasts on the resulting spaghetti of amino acids. As it does, infected animals grow lethargic, shedding their skin in a death spiral that ends with heart failure in a matter of weeks. Some amphibians can tolerate or resist Bd, but the fungus can infect at least 695 species to varying degrees.
“This is pretty unusual for a disease, to see it affect so many different species,” says University of Maryland biologist Karen Lips, an amphibian-decline expert who wasn’t involved with the new study.
In person, Bd infestations can look like biblical plagues. Each August, adult midwife toads in the French Pyrenees climb out of their birth lakes for the first time. The infected toads barely make it to shore. “They’ll do one last hop, and then they’ll expire in your hands,” says Fisher, one of the study’s coauthors. “You can walk the lakes—it’s just carpets of dead frogs.”
Similar die-offs started popping up in the 1970s, but researchers didn’t realize these “enigmatic declines” were a global phenomenon until the 1990s. In 1997, researchers first described Bd, and within a decade, they had connected it to the slaughters. Meanwhile, Bd‘s killing spree continued. From 2004 to 2008, one site in Panama lost 41 percent of its amphibian species to the fungus.
Most of the once-mysterious slaughters are now attributed to the “Global Panzootic Lineage,” a lethal strain nicknamed BdGPL. But where did this killer come from? And when and how did it blaze a trail around the world?
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