Fatal skin fungus found in U.S. frogs.

Chytrid skin fungi, which have devastated frogs in parts of Australia and Central America, have now turned up in the wild in the United States. Early signs hinted that U.S. species might tolerate the infection as no more than a nuisance, but new data from Arizona raise the possibility that chytrids cause die-offs in the United States.

Tissue samples from dead and dying frogs in Arizona--wild lowland leopard frogs and captive Chiricahua leopard frogs, a rare species--show chytrid infection, reports pathologist Donald K. Nichols of the National Zoological Park in Washington, D.C. Large numbers of both species have died off in the wild in the last decade, notes Philip C. Rosen of the University of Arizona in Tucson, who had collected the samples. Just what role the fungus plays is far from clear, but "we're taking it very seriously."

The chytrid fungus made headlines two weeks ago when an international team of scientists fingered it as the culprit in die-offs of 19 amphibian species in pristine tropical streams in Australia and Central America. Details will appear in the July 21 Proceedings of the National Academy of Sciences.

One of these outbreaks, in Panama last year, caught the attention of coauthor Karen R. Lips, now at Southern Illinois University in Carbondale. She collected some 50 dead amphibians during a single trip to Panama and sent samples to D. Earl Green, now at the National Institutes of Health in Bethesda, Md. He found small, round bodies in their skin. "These were quite a conundrum," he says.

Coauthor Lee Berger of the Australian Animal Health Laboratory in Geelong also found the odd structures in wild frogs and toads from Australian die-offs. DNA analysis suggested chytrid fungi, a group not previously known to attack vertebrates.

Meanwhile, another pathology team was also closing in on the fungus. Nichols first noted the fatal skin disease in 1991 in captive arroyo toads in California. In 1996, he saw it in zoo frogs in Washington, D.C., and sent electron microscopy images and samples to mycologist Joyce E. Longcore at the University of Maine in Orono. She recognized the agent as a chytrid fungus and suggested that it represents a new genus.

Nichols has since found low levels of the fungus in wild cricket frogs in Illinois. Likewise, Green found infections in several Maryland specimens of the common American toad. In neither case did the animals appear to be suffering a fatal disease like the Arizona frogs.