African frogs, originally imported for early 20th century pregnancy tests in laboratories and hospitals, carried a deadly disease to the U.S. and is wiping out amphibians around the world , according to a new study published today in the journal PLOS One,

The fungus is called Batrachochytrium dendrobatidis, or Bd for short. Amphibians have been dying in large numbers in every continent except Antarctica since the late 1980s and this fungus has been blamed as a large contributing factor since the late 1990s, according to the study conducted by Stanford University School of Medicine     .

The fungus has led to the recent decline or extinction of 200 frog species worldwide. A previous study found that the earliest case of Bd in the world was found in African Clawed Frogs in their native South Africa in 1934, but until now no research has tested for the disease among this species in populations that have become established in the U.S.

 The African clawed frog can act as a carrier of the fungus without developing symptoms, but Bd is deadly to most other amphibians. The fungal pathogen has been implicated in frog epidemics in a number of countries, including the United States, United Kingdom, France, Spain, Germany, Portugal, Italy, Brazil and Japan, as well as throughout Latin America.

Among 28 samples tested, the researchers identified three frogs, including one found in Golden Gate Park in San Francisco, that were carriers of the pathogen that has led to the decline or extinction of some 200 amphibian species worldwide. The research was conducted on archived samples from the herpetology collection at the California Academy of Sciences in San Francisco.

"Our goal was to document historically how far back this fungus might have existed in California. Until this study, there were no reports to substantiate that Xenopus laevis (African clawed frogs) in California were infected with this fungus," said Sherril Green, PhD, DVM, professor and chair of comparative medicine at Stanford and senior author of the paper.

"I can't think of another disease on the planet more significant than this amphibian disease," says Peter Daszak, president of EcoHealth Alliance, a New York-based group focused on the role of the wildlife trade in the introduction of dangerous pathogens. "No disease of humans has ever wiped us out." But he estimates that the chytrid fungus pandemic has already caused the extinction of more than 100 species, including the golden toad in the cloud forests of Costa Rica, the gastric brooding frog in Queensland, Australia, and 20 or 30 species of brilliantly colored Harlequin frogs in Central and South America. "And it's still causing extinctions."