Researchers Explain the Secret Behind Deadly Fungal Infection

Researchers have discovered the mechanism that allows a fungus to infect and kill entire frog populations.

Batrachochytrium dendrobatidis (Bd) - a type of fungus - has infected several species of frogs. However, some frogs seem to be unaffected by Bd.

A team of researchers from the Cornell University have found the mechanism behind the fungal infection in the highly susceptible Panamanian golden frog (Atelopus zeteki).

The team found several changes in thousands of genes of frogs infected with the fungus. Scientists also found that the pathogen was suppressing genes linked to T-cells, which fight foreign bodies, in the spleen of infected frogs.

"T-cells are being suppressed by the fungus, and that could be a large part of why this fungus is devastating to certain species," Kelly Zamudio, the paper's lead author, the study's senior author and the Goldwin Smith Professor of Ecology and Evolutionary Biology, said, according to a news release.

For the study, the researchers used adult golden frogs from the Maryland Zoo in Baltimore's captive breeding program. The frogs were divided into three groups: control uninfected animals, frogs that were exposed to a weak strain of the fungus and were again infected with a strong strain of the pathogen and naïve frogs that were previously uninfected. The naïve frogs were then exposed to a more virulent strain of the fungus.

The researchers found that frogs infected with more virulent strain died. However, there were several changes in the genes of frogs in the three groups.

The most striking difference was seen in genes that controlled spleen function. Previously, infected frogs had active genes that regulate enzyme production. The enzyme controlled by these genes breaks fungal cell wall.

The study shows that the vulnerable frogs are fighting the fungus, but the pathogen is a step ahead.

"This is the first time we have seen that susceptibility is not a lack of immune response; [the frogs] are responding, but the fungus may be countering these immune responses," which leads to infection, explained Amy Ellison, a postdoctoral research associate in Zamudio's lab.

The study is published in the journal G3: Genes, Genomics, Genetics.

The fungal infection studied in the current research swept through Central America in 2006 and wiped out several populations of the golden frogs. Panamanian golden frogs are almost extinct in the wild now.