A fatal skin fungus, which devastated frogs in parts of Australia and Panama, has turned up in a dying, wild frog in Arizona, according to a University of Arizona researcher.
The discovery of chytrid ("KIT-trid") infection in this lowland leopard frog raises the possibility that the disease has played a role in mysterious amphibian die-offs in the United States, reports the July 4 Science News magazine.
Pathologists had already noted occasional chytrid outbreaks in U.S. zoos. Until now, the few wild amphibians found with the fungus -- in Maryland and Illinois -- did not seem ill. The Arizona frog, however, had a life-threatening illness, reports herpetologist Philip C. Rosen, at the University of Arizona in Tucson. He collected the frog in a relatively undisturbed spot near Cienega Creek.
Pathologist Donald K. Nichols of the National Zoological Park in Washington, D.C. diagnosed chytrid infection. He found the same disease in another species Rosen collected, a fatally ill Chiricahua leopard frog from an outdoor enclosure at San Bernadino National Wildlife Refuge in Arizona.
Both species have suffered die-offs during the last decade, Rosen says. The Chiricahua leopard frog has not bounced back well and has been proposed as a candidate for listing as an endangered species. What role the fungus might have played in these die-offs is far from clear, Rosen says, but "we're taking it very seriously."
The chytrid fungus first made headlines two weeks ago when an international team of scientists fingered it as the culprit in die-offs of 19 species of amphibians in apparently pristine streams in Central America and Australia. Details will appear in the July 21 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.
The Panamanian outbreak caught the attention of Karen Lips of Southern Illinois University in Carbondale during a visit to Panama in 1997. Forest scavengers are so efficient that herpetologists typically find few dead animals lying uneaten during a lifetime of fieldwork, yet Lips collected some 50 during one trip. She sent samples to D. Earl Green, now at the National Institutes of Health. He found odd, microscopic round bodies in the skin. "These were quite a conundrum," he says.
Pathologist Lee Berger at the Australian Health Laboratory in Geelong found the same structures in frogs and toads from Australian die-offs. DNA from the round bodies most closely matched chytrid fungi's, a surprise since scientists had never seen chytrids attack vertebrates.
Meanwhile another pathology team was closing in on identifying the fungus, this time in zoo frogs. Nichols had first spotted the disease in 1991 in captive arroyo toads in California. In 1996, when frogs at the National Zoo caught it, he sent electron microscopy images and tissue samples to mycologist Joyce Longcore at the University of Maine in Orono. "As soon as I saw them, I recognized the organism," she says.
Since then, Nichols has found low levels of the fungus in skin from cricket frogs in Illinois. Likewise, Green found infections in Maryland specimens of the common American toad. In neither case did the animals seem to be suffering from a severe disease like the Arizona frogs.