By David Perlman, San Francisco Chronicle

Biologists have discovered the Typhoid Mary of the frog world – a little green hopper that is spreading a deadly fungus disease to other frogs and amphibians in the Sierra while remaining largely immune to the infection itself.

The fungus, known as chytrid, has killed frogs, toads, salamanders and newts in the Sierra and is the same fungus that has wiped out hundreds of frog species throughout the world in what many biologists have termed a “mass extinction.”

In California, two San Francisco State University researchers have discovered that the common Pacific chorus frog, an amphibian barely an inch long, appears to be the guilty animal. The chorus frogs are heavily infected with the killer fungus, but almost never show symptoms of the disease, biologist Vance T. Vredenburg and Natalie M.M. Reeder, a recent graduate student in his lab, reported in Monday’s online journal PloS One.

Not so for the frog’s neighbors, the yellow-legged frogs that also inhabit Sierra lakes are rapidly being infected and dying with a litany of severe symptoms, including “weight loss, lethargy, excessive skin shedding, muscle spasms and loss of reaction to stimuli,” the researchers said.

The chorus frog is common to California. Its noisy “ribbit” call can be heard from dawn to dusk around lakes from the Bay Area to the High Sierra, but Vredenburg said in an interview that no studies have been done to determine whether the fungus it carries is affecting Bay Area amphibians.

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