African clawed frogs were widely used in pregnancy tests for three decades from the 1930's to the 1950's, and even later. Now, it appears that these amphibians inadvertently carry the chytrid fungus which has led to the extinction of hundreds of other amphibian species.
Biologists have known for years about the chytrid fungus which affected amphibians worldwide. Although a good deal of research and effort has gone into stopping chytrid, or at least preventing its spread, little was known about the origins of the fungus, until now.
Vance Vrendenburg of San Francisco State University led the research team which uncovered how the fungus spread. The group studied the preserved bodies of amphibians which died from the fungus between 1897 and 2010.
The chytrid fungus covers the skin of the amphibian, causing the animal breathing difficulties, and throwing off the creature's electrolyte levels. It can also lead to cardiac arrest.
Marm Kilpatrick, a disease ecologist at the University of California, said the fungus is "the single biggest threat to vertebrae diversity in the world." The researcher went on to state that she believes the same fungus also caused the yellow-legged frog to become endangered and led to the extinction of many species of harlequin frog.
The frogs were used to test for hormonal changes during pregnancy. A sample of the woman's urine was injected into one of the frogs, and if her hormone levels were too high, it would spur egg growth in the amphibian.
Not only were the frogs transported around the globe for use in procedures, but they also found some popularity as pets. The frogs, unknown to their owners, were carriers of the chytrid fungus which would go on to cause tremendous damage to other amphibians.
The African Clawed frog is not alone in its ability to spread the fungus, also known as Batrachochytrium dendrobatidis. The tiny fungal organisms are also carried by the African bullfrog, which is sometimes prepared into food. Over time, many of the frogs either escaped or were let go into the wild, spreading the fungus worldwide.
Vredenburg said of the spread of the alien frog species, "There are populations here in Golden Gate Park, in San Diego, Los Angeles, Europe, China, nearly everywhere."
The study was published by PLOS ONE, a peer-reviewed online science journal.