Some tropical frogs may be developing resistance to a deadly fungal disease – but now salamanders are at risk
Posted by admin on 16th May 2018
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My office is filled with colorful images of frogs, toads and salamanders from around the world, some of which I have collected over 40 years as an immunologist and microbiologist, studying amphibian immunity and diseases. These jewels of nature are mostly silent working members of many aquatic ecosystems.

The exception to the silence is when male frogs and toads call to entice females to mate. These noisy creatures are often wonderful little ventriloquists. They can be calling barely inches from your nose, and yet blend so completely into the environment that they are unseen. I have seen tropical frogs in Panama and native frogs of Tennessee perform this trick, seemingly mocking my attempts to capture them.

My current research is focused on interactions between amphibians and two novel chytrid pathogens that are linked to global amphibian declines. One, Batrachochytrium dendrobatidis ( abbreviated as Bd), has caused mass frog dieoffs around the world. Recently my lab group contributed to a study showing that some species of amphibians in Panama that had declined due to Bd infections are recovering. Although the pathogen has not changed, these species appear to have developed better skin defenses than members of the same species had when Bd first appeared.

This is very good news, but those who love amphibians need to remain vigilant and continue to monitor these recovering populations. A second reason for concern is the discovery of a closely related chytrid, Batrachochytrium salamandrivorans (Bsal), which seems to be more harmful to salamanders and newts.

Amphibian chytrid fungus has been detected in at least 52 countries and 516 species worldwide.
USDA Forest Service

Global frog decline

More than a decade ago, an epidemic of a deadly disease called chytridiomycosis swept through amphibian populations in Panama. The infection was caused by a chytrid fungus, Batrachochytrium dendrobatidis. Scientists from a number of universities, working with the Smithsonian Tropical Research Institute in Panama, reported that chytridiomycosis was moving predictably from west to east from Costa Rica across Panama toward Columbia.

I was part of an international group of scientists, funded by the National Science Foundation, who were trying to understand the disease and whether amphibians had effective immune defenses against the fungus. Two members of my lab group traveled to Panama yearly from 2004 through 2008, and were able to look at skin secretions from multiple frog species before and after the epidemic of chytridiomycosis hit.

Many amphibians have granular glands in their skin that synthesize and sequester antimicrobial peptides (AMPs) and other defensive molecules. When the animal is alarmed or injured, the defensive molecules are released to cleanse and protect the skin.

Through mechanisms that remain a mystery, we observed that these skin defenses seemed to improve after the pathogen entered the amphibian communities. Still, many frog populations in this area suffered severe declines. A global assessment published in 2004 showed that 43 percent of amphibian species were declining and 32 percent of species were threatened.