The rise of a frog-killing fungus pinned in part on global trade

Justin C. Touchon, Smithsonian Tropical Research

It’s a tough time to be a frog. A fungal disease known as chytridiomycosis has been decimating populations across the planet for about a decade. Since its discovery in the late 1990s, it has already wiped out about 100 species. Although it seemed to appear suddenly, a team of scientists has now published the evolutionary history of the fungus, which suggests that chytridiomycosis has been killing amphibians for thousands of years.

The fungus, Batrachochytrium dendrobatidis, damages amphibian skin, often with fatal consequences, because these creatures use their skin to absorb water and electrolytes they need. The infection spreads primarily through skin-to-skin contact, but a form of the fungus called a zoospore can persist in wet environments for months. Though the spread and impact of the disease have been well-documented, the reason for the rising infection rate remained under debate.

When a scary new infectious disease starts spreading, scientists need to learn why the pathogen has suddenly become so deadly in order to understand how to protect at-risk populations. Epidemiologists know that a deadly disease doesn’t just emerge from thin air—either an existing pathogen evolved into a new, more virulent form, or something about the affected species or its environment has changed to increase its susceptibility.