A species of frog, the African clawed frog (Xenopus laevis), initially used from the 1930s for human pregnancy tests, has been found to be a carrier of a deadly amphibian disease that now threatens hundreds of other species of frogs and salamanders worldwide.
This species of frog was originally shipped across the globe for the use of pregnancy tests until the early 1970s after different methods were established. Originally, if a woman suspected she was pregnant, her urine sample would be injected into a female South African clawed frog to medically assess a positive or negative result. If the frog began to ovulate within 10 days, it was likely the woman was pregnant.
After newer testing technology became available, the frogs were released into the wild on multiple continents. Ever since their release, millions of other frogs and salamanders have succumbed to the deadly fungus the African claw frogs carried, called Batrachochytrium dendrobatidis (Bd).
Bd infects the skin and causes it to thicken up to 40 times. After a couple weeks the thickening results in an electrolyte imbalance and the amphibians ultimately die from heart attacks. Researchers have yet to find a cure.
According to Dr. Vance Vredenburg – a conservation biologist at San Francisco State University and one of the researchers involved in a related study of Bd published in the journal PLOS One – “There are populations here in Golden Gate Park, in San Diego, Los Angeles, Europe, China, nearly everywhere.”
A 1934 museum specimen of an African clawed frog tested positive in 2004 for Bd. Other preserved DNA samples dating as far back as 1871, well before the frogs were ever shipped, also tested positive for the presence of Bd. Today these frogs are still used for research or kept as pets.
There are other possible carriers of Bd, including the American bullfrog, which has also been moved around the world by people who farm bullfrogs for their meaty legs, reports NBC News.
Thus far the pathogen has been responsible for the recent decline or extinction of 200 other types of frogs, but it appears African clawed frogs are asymptomatic hosts, unaffected by the fungus. Researchers surmise their immunity was out of years of evolution – the species suffering the ill-effects only to eventually survive like humans have with certain diseases. But for others, Bd could likely continue to decimate amphibian populations.
[Image via Wikicommons by Tim Vickers]