An Amphibian Fungus Has Become 'The Most Deadly Pathogen Known To Science'

'On Thursday, 41 scientists published the first worldwide analysis of a fungal outbreak that's been wiping out frogs for decades,' The New York Times reports. The outbreak has caused more than 500 species of amphibians to decline significantly (Warning: source may be paywalled; alternative source), making it 'the most deadly pathogen known to science.' From the report: Scientists first noticed in the 1970s that some frog populations were declining quickly; by the 1980s, some species appeared to be extinct. The losses were puzzling, because the frogs were living in pristine habitats, unharmed by pollution or deforestation. In the late 1990s, researchers discovered that frogs in both Australia and Panama were infected with a deadly fungus, which they named Batrachochytrium dendrobatidis -- Bd, for short. The fungus turned up in other countries, but studies of its DNA suggest that Bd originated on the Korean Peninsula. In Asia, amphibians seem impervious to Bd, but when it got to other parts of the world â' probably via the international trade in pet amphibians -- the pathogen reached hundreds of vulnerable species.

Amphibians are infected with Bd by contact with other animals or by spores floating in the water. The fungus invades skin cells and multiplies. An infected frog's skin will start to peel away as the animal grows sluggish. Before it dies, a frog may manage to hop its way to a new stream or pond, spreading the fungus further. The fungus thrives in cool, moist conditions. As a result, frogs that live in cloud forests on mountainsides have been hit particularly hard. Big frogs are at a greater risk, too, possibly because they don't multiply as quickly as small ones. [The lead author of the new study and his colleagues] identified 501 species in decline, far greater than the previous estimate of 200. Certain factors once thought to account for the decimation of frog populations -- like climate change and deforestation -- are not the greatest threats, the scientists found. The study has been published in the journal Science.

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