11 July 2018

Origin found of amphibian’s worst nightmare, Batrachochytrium Dendrobatidis

Posted by Shane Hanlon

This is part of a series of posts from our own Shane Hanlon’s disease ecology class that he’s currently teaching at the University of Pittsburgh Pymatuning Laboratory of Ecology. Students were asked to write popular science posts about (mostly) wildlife diseases. Check out all the posts here

By Alex Landis

In recent years, amphibians all over the world have been dying to the fungus Batrachochytrium dendrobatidis, affectionately referred to as BD. The fungus has been spreading at an alarming rate, and the death toll is rising. The sudden and dramatic outbreak of BD around the world has prompted a large-scale research effort to locate the origin of the fungus, which may reveal the genetic lineage of the fungus, as well as give us insight into preventing further spread of the disease.

An international team of scientists spent months gathering BD samples from hundred of wild and captive amphibians from Australia, North and South America, Africa, Asia, and Europe. They concluded that the fungus likely originated from East Asia at the beginning of the 20th century.

Gray tree frog. Credit: Wiki Commons

An infection of the BD fungus, which belongs to the rather virulent phylum of fungi Chytridiomycota,  can cause osmotic imbalance, organ failure, and death, and has been attributed to multiple relatively recent mass die-offs within the amphibian class. It is unknown why this division on fungi has suddenly surfaced as an ecological threat. Some speculate that changes in climate have created an ideal environment for it’s growth and proliferation. Another theory is that the ever-growing “globalization” of our culture, i.e. ease of intercontinental travel, has facilitated introduction of novel BD strains to un-adapted amphibian populations. While the research project doesn’t address these specific issues, uncovering the origins of the fungus is a key part of understanding how it interacts with the environment.

One notable part about the experiment is that it was incredibly difficult to culture the disease. Though the fungus is incredibly invasive and virulent in the wild, the research team had a difficult time culturing BD in the lab. Out of 450 attempts to isolate the fungus, only 3 were successful.

From the assessment of the BD genome, the scientists concluded that BD likely emerged from East Asian anywhere from 120-50 years ago, which coincides with the beginning of the global amphibian trade. The results suggest that as a scientific community, we need to focus our efforts on preventing further spread of BD through limiting the movement of these infected animals.

While BD is already present around the world, scientists have identified several hybrid strains, which could wreak further havoc on amphibian species. BD has already escaped its homeland, however it is not too late to halt the spread of the various virulent strains of the fungus that have emerged recently.