Frogs make a comeback, beat fungus

Enlarge / In the US, biologists are keeping watch for the amphibian-killing fungus. (credit: USGS)

Epidemics proceed with different dynamics. Sometimes they spike rapidly and disappear gradually; sometimes they ramp up slowly; sometimes they have multiple waves. What they all do at some point is end, usually with neither the pathogen nor the host going extinct. But we don't usually understand how or why.

Chytridiomycosis is an epidemic that has been killing amphibians the world over for at least a decade. It is caused by a fungal pathogen called Batrachochytrium dendrobatidis (Bd), and it can cause limb deformities and skin abnormalities. Since amphibians absorb water and electrolytes through their skin rather than their mouths, such abnormalities can be fatal. But now we have some evidence that, as with past epidemics, Bd isn't a one-way ticket to extinction.

Between 2004 and 2007, Bd decimated frog populations in Panama. About five years later, however, frog populations rebounded. Bd was still around, although it was not nearly as prevalent. Scientists collected frog and fungus samples from the start of the outbreak, in 2004, and after the recovery, in 2013, in order to figure out what factors went into making this particular epidemic subside. They hypothesized that either (a) the later Bd samples would be less pathogenic to the frogs; (b) the later frog samples would be more resistant to Bd; or (c) both.

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