Frog-killing fungus confirmed as an African import

African clawed frog, Xenopus laevis

Scientists have long suspected that the deadly fungus disease that is killing millions of New World amphibians came form Africa.

Thursday a scientific research paper offered proof and said that the fungus, Batrachochytrium dendrobatidis, came to the Americas on the skin of African clawed frogs that were being used for pregnancy tests in the early 20th century.

Costa Rican frog populations have been wiped out by this fungus, which first became known here in the early1980s. Scientists have blamed pesticides, global warming and other factors, too. Among the victims are the golden toad (Bufo periglenes) which vanished in 1988 and the the harlequin frog (Atelopus varius) which vanished in Monteverde, as AmphibiaWeb of the University of California, Berkeley. notes online.

The confirmation of the origin of the fungus came from researchers at San Francisco State University in California.

From the 1930s to 1950s, thousands of African clawed frogs were exported across the world for use in pregnancy tests, scientific research and the pet trade. These frogs will ovulate when injected with a pregnant woman’s urine, reported biologist Vance Vredenburg. Modern pregnancy tests did not replace the frogs until the early 1960s in some countries.

Vredenburg and colleagues swabbed genetic material from the skins of preserved frogs that have been captured from 2001 to 2010. Then they also tested archived specimens collected in Africa since 1871 and found evidence confirming that the fungus was present among native populations of this species before they were exported worldwide, said the university. The African clawed frog appears to be able to live some time even when infected. Although no longer used in pregnancy testing, African clawed frogs (Xenopus laevis) are still imported to the United States for use in biomedical and basic science research, according to the university. Because of their suspected role as a carrier of the fungus and other potential pathogens, 11 U.S. states already have restricted the importation of these frogs, for example by requiring special permits and not allowing them to be sold as pets, it added.

The fungus, Batrachochytrium dendrobatidis, has been detected by researchers here even in the high Talamanca mountains, according to research at the Universidad Nacional in Heredia.

The AmphibiaWeb source reports that as many as 200 species of frogs have been wiped out by the fungus even in pristine, remote habitats. And the disease has been implicated in the unexplained disappearances of Central American salamanders as well, it said.

The fungus has been in Costa Rica since at least 1986 when it was located on Costa Rican museum amphibian specimens dating from then.

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