What is the Frog-Killing Fungus?

The term “amphibian crisis” is becoming increasingly prominent as amphibians continue to decline. As with other wildlife, amphibian populations have been declining for decades. Despite the fact that amphibians have existed since before the dinosaurs, scientists estimate that one-third of amphibian species are threatened and that 43% of species are currently declining in population.

At play here are the usual suspects of pollution and habitat destruction. But frogs are facing a unique challenge: A fungus. A fungus that kills frogs and spreads everywhere.

The Frog-Killing Fungus

A 2019 study concluded that the fungus Batrachochytrium dendrobatidis (or Bd for short) is responsible for the worldwide decline of “at least 501 amphibian species over the past half-century, including 90 presumed extinctions.”

The spores of Bd infect the frog's skin and extract nutrients from it, causing a disease known as chytridiomycosis. The fungus releases more spores, many of which reattach to the frog's skin, spreading the infection. As the fungal infection grows, it interferes with the frog’s respiration, heart function, and other bodily processes. Frogs die about 2 weeks after infection, often of cardiac arrest. Others die of starvation because they become so weak and disoriented that they cannot catch food.

More bad news is that the fungus spreads easily. The fungal spores can survive for weeks in water, during which time they can attach themselves to a host (or to an unaffected carrier such as the feet of water birds) and be transported to a new location. Even among frogs, not all species are equally affected by Bd, meaning that more resilient species may act as carriers. Human activity can also spread Bd – for example, thousands of frogs per year are accidentally carried in produce boxes, and some of these frogs could be host spreading the fungus to a new location.

Can Scientists Fight Bd?

Since its discovery in 1998, scientists have worked to uncover the impact of Bd and how it spreads. Infected frogs can successfully be cured in a laboratory, but that is not a sustainable wide-scale strategy, especially since frogs can become re-infected after being released into the wild. Because our lab treatments are unfeasible to carry out in the wild, there currently exists no method of eradicating large areas of Bd in nature.

Where Do We Go From Here?

Although amphibians’ current situation is bleak, there are glimmers of hope. For example, scientists are investigating how the naturally occurring bacteria on frogs’ skin can help protect frogs from Bd. There are also experiments wherein frogs are exposed to less-virulent forms of the virus, prompting them to develop immunity. Captive-breeding programs can help maintain a species’ populations even if it is critically endangered or extinct in the wild.

There are also steps that every one of us can take in order to reduce the spread of Bd. For example, conservation officials urge people to disinfect footwear and other equipment with a bleach solution (1:20 bleach-to-water ratio) after hiking, camping, or other outdoors activities. It’s critical that people not release pet amphibians into the wild, as this is not only cruel to the amphibian being left in an alien environment, it also risks introducing disease to local wildlife populations. If you see a frog (alive or dead) that you suspect is infected with Bd, you can report it to a local environmental authority such as your state’s department of natural resources.