Frog Fungus: Researchers Decode a Deadly Disease

A quiet and deadly infection has been sweeping across amphibian populations for the past decade, utterly decimating some groups on a pandemic scale and utterly overlooking others. So what's going on here? Now researchers look to genetics for the answer.

A study recently published in the journal G3: Genes, Genomics, Genetics details an investigation into the mechanics of the fungus Batrachochytrium dendrobatidis, commonly referred to as a "Bd" infection.

The researchers assessed how a Bd infection affects the expression of genes in the Panamanian golden frog (Atelopus zeteki) in particular, as this is a species found to be highly susceptible to the fungus.

Almost immediately into their work, researchers from Cornell University successfully identified significant changes in thousands of genes of infected frogs who later died, when compared to the uninfected and even survivor groups.

They found that the infection could be targeting immune genes related to pathogen-fighting T-cells in particular - making it an exceptionally proficient killer.

"T-cells are being suppressed by the fungus, and that could be a large part of why this fungus is devastating to certain species," Amy Ellison, the study's lead author, explained in a recent statement.

They also discerned that genes that control inflammation in the frog's skin were also being excited into heightened activity by the infection.

"This is not necessarily a good thing," Ellison added, "since severe inflammation may be pathological."

Bd's base of operations, it seems, is in the spleen, where T-cell production was particularly targeted. Even more interesting, when the survivor group was condemned to death with a more virulent strain of the infection, the spleen's genes that control enzymes involved in breaking down chitin - one of the main components of fungal cell walls - were found to be more active. This could indicate that the frog's body was catching on to how to fight the illness, but was still unprepared for the aggressiveness of the second strain.

"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," Ellison explained.

With these reults in hand, she and her colleagues will now move on to assess the fungus in resistant species.