June 17, 2013 — Amphibian populations are declining worldwide and a major cause is a deadly fungus thought to be spread by bullfrogs, but a two-year study shows they can also die from this pathogen, contrary to suggestions that bullfrogs are a tolerant carrier host that just spreads the disease.
When researchers raised the frogs from eggs in controlled experimental conditions, they found at least one strain of this pathogen, Batrachochytrium dendrobatidis, also called Bd or a chytrid fungus, can be fatal to year-old juveniles. However, bullfrogs were resistant to one other strain that was tested.
The findings, made by researchers at Oregon State University and the University of Pittsburgh, show that bullfrogs are not the sole culprit in the spread of this deadly fungus, and add further complexity to the question of why amphibians are in such serious jeopardy.
About 40 percent of all amphibian species are declining or are already extinct, researchers say. Various causes are suspected, including this fungus, habitat destruction, climate change, pollution, invasive species, increased UV-B light exposure, and other forces.
"At least so far as the chytrid fungus is involved, bullfrogs may not be the villains they are currently made out to be," said Stephanie Gervasi, a zoology researcher in the OSU College of Science. "The conventional wisdom is that bullfrogs, as a tolerant host, are what helped spread this fungus all over the world. But we've now shown they can die from it just like other amphibians."
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