The African clawed frog, which was used to determine pregnancy in early 20th century, is reportedly carrying a deadly fungal disease infecting other species of frogs and salamanders, according to a new research.

The African clawed frogs, also termed as Xenopus laevis, and used for pregnancy detection in early 20th century, have almost led to the extinction of many amphibian species across the world.

Found in the south-eastern portion of Sub-Saharan Africa, these frogs were widely used as pregnancy detectors and imported to many countries. These frogs could produce eggs (ovulate) within about 10 hours of being injected with pregnant women's urine. Later when better ways were introduced these frogs were freed in the wild. But now, researchers have realized that the African clawed frogs are posing a threat to other species of frogs and salamanders across different continents.

The African clawed frogs are carrying a fungus named Batrachochytrium dendrobatidis, or Bd, according to the researchers. The African frog is a hardy species and does not seem to be affected by the fungus.  However, it has adverse effects on other species of frogs and salamanders as the infection results in thickening of the skin by up to 40 times than normal, according to Vance Vredenburg, a conservation biologist at San Francisco State University and one of the researchers involved in the study. It causes heart attacks in these species in just weeks after the infection. This has resulted in decline or extinction of nearly 400 species of frogs across the globe, according to Science Recorder.

"Evolution has run its course," Dr. Vredenburg said. "The species probably at some point suffered, but the survivors have figured out ways to survive."

Due to the import of these African clawed frogs, they are found everywhere including the U.S, Europe, and China and "the worst disease in vertebrate history," Vredenburg told the New York Times.

The infection came to light after researchers tested the DNA samples of African clawed frogs' skin at the California Academy of Sciences in San Francisco and found the occurrence of the disease. The frogs contained the disease before they were exported out of Africa, researchers said after testing the specimens in Africa collected between 1871 and 2010.

"We really need to understand the fundamental biology here," Vredenburg said. "That same biology is occurring in other kinds of pathogens."

The research was published today in the journal PLoS One.