Batrachochytrium dendrobatidis (Bd) is a deadly skin fungus that seriously threatens populations of frogs and salamanders around the world. There may be new hope for catching it early enough to limit amphibian fatalities, however, thanks to the analysis of what's known as environmental DNA.

Called eDNA for short, environmental DNA is released as animals excrete bodily waste, slough off their skin, or otherwise shed bits of their genetic material into the environment. In previous studies, scientists have studied the eDNA content of water bodies to determine what types of fish were passing through, and to detect the presence of invasive clams.

In 2015, Washington State University grad student Colleen Kamoroff utilized eDNA analysis to find out if non-native fish had been successfully removed from lakes in California's Sequoia Kings Canyon National Park. One month after she collected her water samples, there was a Bd-caused mass die-off of endangered mountain yellow-legged frogs in three of those lakes.

"I was curious if Bd would be detectable at the lakes I took samples from even though there were no sick-looking frogs at the time," she says. "So I decided to run the eDNA samples I originally collected for the lake restoration project to test for the presence of Bd."

Sure enough, Bd eDNA showed up in samples from the lakes where the die-off later occurred, but not in samples from the non-affected lakes. Had wildlife officials known about it at the time, it's possible that preventative action could have been taken.

"If we can predict when an outbreak is imminent, we can proceed with management actions such as anti-fungal baths that kill Bd," says Colleen, who now works as a wildlife biologist at Yosemite National Park. "Mountain yellow-legged frogs in the Sierra Nevada have experienced a population decrease of over 90 percent in recent years. Environmental DNA could help save these frogs and other species of amphibians around the world from extinction."

Currently, the only other way of detecting Bd is to physically capture afflicted frogs and take skin swabs from them.

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