Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 33, Number 4;   April, 2006

Human Pregnancy Test Link to Frog Fall

Washington D. C. -- A disease threatening amphibians worldwide may have spread because of the use of frogs in pregnancy tests. The theory is being debated at a summit in Washington DC where scientists hope to produce an action plan to conserve frogs, toads and salamanders. In the 1930s, African frogs were exported for use in human pregnancy tests, and it is suggested they may have carried a fungal disease with them.

The spread of chytridiomycosis is now a major cause of amphibian decline. Chytridiomycosis is caused by the fungus Batrachochytrium dendrobatidis, but where the fungus originated and how it spread have not been established. The link to pregnancy testing was proposed last year by a group of researchers led by Professor Rick Speare, of James Cook University in Townsville, Australia. They examined specimens of a South African clawed frog, Xenopus 1aevis, in museums in southern Africa. They found evidence of Batrachochytrium in specimens dating back to 1938. They also showed that the incidence of fungal disease in Xenopus in southern Africa had not changed since 1938. This suggests that frog and fungus had co-existed for a long period, with Xenopus developing the ability to resist infection. "The idea makes sense," said Dr Peter Daszak, co-chair of the working group on disease at the Washington meeting. "This is the oldest record of the fungus anywhere, so it could be the origin."

In the 1930s and 4Os, live female Xenopus frogs were used widely in Europe, Australasia and north America in pregnancy testing. A sample of the woman's urine was injected under the frog's skin; if the woman was pregnant, a hormone in her urine caused the frog to ovulate. Thousands of Xenopus were exported from Africa each year, potentially carrying Batrachochytrium with them, and - perhaps through occasional escapes - delivering it to the habitats of other continents, where it could inflict major damage on amphibian species that were more vulnerable. The origin and transmission of Batrachochytrium are key topics at the summit here, which concluded on September 19th with the release of an action plan aimed at stemming the global decline in amphibians, which sees more than 1,800 species facing extinction.

"We still don't know how it causes death, and we need to know that," said Dr Daszak, director of the Consortium for Conservation Medicine in the US. "It may hamper oxygen uptake through their skin, though that's not so certain now. Alternatively it may block osmo-regulation (the flow of salts through the skin, which then upsets the salt balance) or it may release a toxin, and there's evidence for that, too." Understanding how some amphibians become immune to fungal infection could be a starting-point for the development of treatments or even vaccines.