Magazine article Science News

Tadpole Slayer: Mystery Epidemic Imperils Frogs

Magazine article Science News

Tadpole Slayer: Mystery Epidemic Imperils Frogs

Article excerpt

From Alaska to Florida, a novel and yet-unnamed protozoan is knocking off tadpoles. Species vulnerable to "the beast" belong to the genus Rana, which includes leopard frogs, green frogs, and bullfrogs, says ecologist John C. Maerz.

His team at the University of Georgia in Athens stumbled across mass die-offs of southern leopard frog tadpoles in nearby ponds last year. Dissection showed the animals' innards peppered with spherical, one-celled parasites. Genetic testing confirmed these are loosely related to Perkinsus,

a disease-causing organism that affects marine shellfish.

Maerz' group now offers the first published photos of the pathogen and descriptions of its effects in the current issue of EcoHealth. Infected tadpoles become lethargic and developmentally stunted, the Georgia scientists report. Although the mystery parasite infects all organs, it clusters in the liver, sometimes tripling that organ's size and giving the false impression that an animal is fat and robust. So many protozoa swamped and killed tissue in the liver of one sick tadpole, Maerz recalls, that throughout most of the organ "we could find no identifiable liver cells."

He notes that his team did not discover the pathogen. It was first found by veterinary pathologist D. Earl Green of the National Wildlife Health Center in Madison, Wise., part of the U.S. Geological Survey.

Since 1999, Green has quietly been recording a steady and growing incidence of the novel infection in frogs sent to his lab. …

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