13 September 1999

Frog deaths may be caused by a fungus infection

by Kate Melville

Recent deaths of many endangered toads in the Rocky Mountains has been linked to a chytrid fungus that was identified as being responsible for amphibian die-offs in Central America and Australia, according to pathologists from the United states Geological Survey (USGS) National Wildlife Health Center.

The sick and dying toads in Colorado were first discovered in 1999 by Colorado Wildlife researchers, who have been intensively studying them for the last five years. Since May 1999, dead toads have been found every month at the site on private lands west of Denver. USGS researchers said they have identified chytrid fungus in many of the dead and living toads they examined. Live toads show few clinical signs of the disease, but appear weak, lethargic and reluctant to flee approaching humans.

Dr. Earl Green, a USGS pathologist, examined many of the dead toads and identified myriads of minute chytrid fungi in the skin of the abdomen and toes of the toads. His microscopic identification of this fungus is being confirmed by collaborative work undertaken by Dr. Joyce Longcore, a chytrid expert from the University of Maine.

This problems may seem samll beer in the general scope of things but it prompted US Secretary of the Interior Bruce Babbitt to call these recent die-offs a, "poignant reminder" that amphibian populations in this country and in many other parts of the world are undergoing severe, unexplained declines.

In the past decade, the international scientific community has increasingly expressed concern over global population declines in all amphibian groups on many continents. These well documented losses have occurred in a wide range of habitats, ranging from remote and areas of California and Arizona to Panama, Puerto Rico and Australia.

"These incidences are disturbing and raise questions about why this fungus is proving so deadly at this time and what other factors might be at work behind the scenes," Secretary Babbitt said. "We need to better understand the inter-relationships in this environmental puzzle and what we can do to fix the situation."

Chytrid fungus in amphibians was first identified in 1998 by researchers who discovered that this fungus had been responsible for large amphibian die-offs. The fungus was also identified in some amphibian populations in Arizona and has caused the death of many zoo-kept amphibians in the United States.

Scientists don't know how this fungus is transmitted from one area to another, let alone why the fungus is affecting amphibian populations around the world. Whether its is responsible for the frog or toad mortality or the declines of frogs and toads in many western states is still unknown. Fungal infections are often considered secondary infections in other vertebrates, USGS is completing further testing for viruses, parasites and bacteria to rule out other factors that could predispose the animals' susceptibility to the fungus.