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By Reuters and Associated Press

Scientists have identified a new problem for amphibians, which are already shrinking in numbers: A parasite is infesting tadpoles worldwide. The family of parasites, related to a bug that attacks oysters, has been found in the livers of frogs and tadpoles on three continents and in both temperate and tropical climates. Researchers linked it to a mass die-off of tadpoles in a Georgia lake.

"There have been numerous outbreaks with this parasite, what we presume to be the same parasite, all over the eastern part of the United States," said University of Georgia wildlife ecology professor Michael Yabsley, co-author of a study published Monday by the Proceedings of the National of Academy of Sciences. "It's certainly going to be one of the things we are worried about for the long-term health of amphibians."

This handout image provided by Michael J. Yabsley, University of Georgia is from the liver of a tadpole that died in 2006 as part of a mass die-off in a lake in Athens, Ga., and magnified 100 times. The purple dots are stained parasites that have now turned up in frogs and tadpoles worldwide.University of Georgia/Michael J. Yabsley via AP

Thomas Richards of Exeter University, who co-led the study, said amphibian numbers are already falling because of habitat loss, climate change, fungus and other diseases. He said this new parasite is "just one more threat."

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"Global frog populations are suffering serious declines and infectious disease has been shown to be a significant factor," said Richards. "We now need to figure out if this novel microbe causes significant disease and could be contributing to the frog population declines."

Amphibians are the family of animals that include frogs, toads, newts and salamanders. Richards said it is still unclear how big a problem the parasite is. That's because 99 percent of tadpoles don't make it to frogs anyway, being eaten by predators, he and Yabsley said.

Amphibians are among the most threatened of all animal groups. In 2008, 32 percent of frog species were categorized as threatened or extinct and 42 percent were listed as in decline.