Deadly Amphibian Fungus is Killing the Same Bullfrogs That Host It

A deadly amphibian fungus is, surprisingly, being spread by the same frogs that it's killing, according to the results of a two-year study by researchers at Oregon State University and University of Pittsburgh.

Bullfrogs are believed to be spreading a pathogen called Batrachochytrium dendrobatidis, also called Bd or a chytrid fungus, which is associated with declining amphibian populations around the world. It has been suspected that the bullfrog has immunity to Bd, as the fungus, regardless of the strain, shows up considerably less in bullfrogs than other species. But the latest research shows that while the bullfrogs are resistant to one Bd strain, a separate strain is fatal in one-year-old juveniles.

Nearly 40 percent of all amphibian species are declining or already extinct, the researchers report. They cite the Bd pathogen, habitat destruction, pollution, climate change predation by invasive species and other forces at play in the loss of amphibians, but the new research takes some of the blame off the bullfrog.

"At least so far as the chytrid fungus is involved, bullfrogs may not be the villains they are currently made out to be," Stephanie Gervasi, a zoology researcher in the OSU College of Science, said in a statement.

"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."

The researchers suggest that the bullfrog is not as good of a host as previously believed; bullfrogs were indicted as a carrier of the fungus when it was discovered in 1998.

But it is still unclear why the killer fungus has spread as far and as quickly as it has.

"One possibility for the fungal increase is climate change, which can also compromise the immune systems of amphibians," said Andrew Blaustein, a distinguished professor of zoology at OSU and leader in the study of amphibian declines. "There are a lot of possible ways the fungus can spread. People can even carry it on their shoes."

The researchers concluded that while bullfrogs may be hosts of Bd in some areas, different hosts may be as or more important in other locations.

The research was published in the journal EcoHealth.