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An animal once used as a pregnancy test may be 'the Typhoid Mary of the frog world'

Xenopus laevis | African Clawed Frog
Xenopus laevis | African Clawed Frog
Photo by Brian Gratwicke via Flickr Creative Commons

Mercury News reports that an African frog imported decades ago to California for medical testing may be the "Typhoid Mary of the frog world," according to a new a Stanford/SFSU study published Thursday in the journal Plos One.

According to researchers, the African clawed frog carries a deadly fungus that is responsible for the decline and extinction of approximately 200 amphibian species around the world.

Bay Area scientists believe they have discovered the Typhoid Mary of the frog world: a flat, feral creature that carried a deadly fungus from Africa to California's ponds and puddles through global trading.

Genetic analysis revealed that eight of 206 African clawed frogs -- caught wild or preserved in jars at the California Academy of Sciences -- carried the fungal plague called chytridiomycosis, which leaves them unharmed but kills native frogs in catastrophic numbers.

The theory is that the deadly fungus thrived in Africa and then spread worldwide. The infection was detected in a frog captured in Africa 1934; A recently infected frog was found alive in Golden Gate Park's Lily Pond.

Researchers spent hours in the basement of the California Academy of Sciences sorting thousands of specimen jars of old, dead frogs — some of which had been floating there in ethanol since 1871. DNA swabs were taken from the skin in between toes and around claws.

The frogs were first brought to the U.S. in the early 20th century to be used as pregnancy tests; they were injected with urine from female patients. When the practice was discontinued, the animals may have been released into the wild.

Bullfrogs have also been implicated in this worldwide spread of amphibian death and mayhem, according to a University of Michigan study, reports the Mercury News.

The fungus is particularly tough on the thin-skinned creatures. Called Batrachochytrium dendrobatidis, or "Bd," it kills frogs by clogging their pores, deranging their blood chemistry and causing their tiny brains to swell.

The infection has led to the recent decline or extinction of 200 frog species worldwide, from the Sierra yellow-legged frog to the exotic jewel-colored creatures that decorate calendars, postage stamps and National Geographic magazine covers. 

Scientists have not yet come up with a protective solution, or a way to transfer the resilience displayed by some frogs to the more vulnerable species.

Containing the worldwide epidemic is "a major challenge," according to study collaborators who say the fungus can also be spread through water, wind and on bird feathers.

The frogs' use, sale and transport are now highly regulated in California, but the damage has been done, they said. (A pygmy version, a favorite of aquarium enthusiasts, is less hardy, so it's not considered a threat.)

In the late 1980s, the L.A. Times published a story called "Predatory and voracious, the 'little eating machines' thrive in Santa Clara River despite a 15-year eradication campaign. : African Frogs Remain Kings of the Canyon," reporting on their decimation of a fish population:

The camouflage-green frogs are decimating the last known population of the unarmoured threespine stickleback, a tiny endangered fish found only where the Santa Clara River flows through Soledad Canyon.

Harvey Fischer, the curator of reptiles and amphibians at the Los Angeles Zoo at the time, said of the species, "They're just little eating machines," noting that the creature can grow to about eight inches (with legs extended) and use three claws on each hind leg to, "shred their prey."

The University of Michigan's comprehensive Museum of Zoology Animal Diversity Web database has a detailed fact sheet on the invasive species and its impact, geography, physical development, lifespan, behavior, diet, reproduction and habitat.