The Frog That Unleashed the World's Most Lethal Pathogen

In the 1920s, South African scientist Lancelot Hogbin investigated African clawed frogs (Xenopus laevis) as model organisms for hormone and developmental biology studies, focusing on their adaptive skin pigmentation.

South African researchers in 1938 developed the Xenopus pregnancy test using African clawed frogs, following the discovery that ox pituitary extract caused female frogs to eject hundreds of unfertilized eggs within hours.

Australian amphibian population surveys in the late 1970s detected the first signs of BD impact. Scientists discovered hundreds of dead southern day frogs and southern gastric brooding frogs in streams near Brisbane’s upland rainforests. Gastric brooding frogs, which uniquely incubated offspring in the mother’s stomach, vanished entirely by 1981.

Museum specimen testing conducted in 2004 traced Batrachochytrium dendrobatidis (BD) proliferation to the 1930s in Africa, coinciding with global distribution of African clawed frogs for pregnancy testing. The African clawed frog served as the primary asymptomatic vector.

Batrachochytrium dendrobatidis (BD), identified in 1999, is an obligately parasitic aquatic fungus that completes its entire life cycle exclusively on amphibian skin. It differs from most aquatic fungi, which feed on algae or decaying matter rather than living vertebrates.

Batrachochytrium dendrobatidis causes cutaneous chytridiomycosis, a lethal skin disease affecting amphibian respiration and osmoregulation. The disease was identified in 1999 following parallel investigations of mass die-offs in Australia and Panama.

Conservation biologists are developing multiple approaches to help amphibian populations survive BD, which has become a permanent component of infected ecosystems. Researchers recognize that BD eradication is probably impossible, necessitating strategies for coexistence.