A Great Leap Forward

Frogs and toads throughout the world are being killed by a fungus that is new to science. The fungus, which coats their undersides and legs, is thought to be suffocating the animals, which breathe through their skins. It could be a major factor underlying the decline in amphibian populations reported worldwide.

The fungus has been found independently by teams in the US and Australia. It belongs to a new genus of chytrid, a group thought to be related to the earliest fungi. Although other chytrids parasitise a range of organisms, from microscopic algae to insects, they have never before been found to cause disease in vertebrates.

The fungus, which has yet to be given a scientific name, is known to have struck down 10 species of frogs and toads from 10 locations in Australia, seven species from two locations in Panama, a toad from southern California, and six species of frogs in four American zoos and aquariums. "There's little doubt that this is a worldwide phenomenon," says Allan Pessier, a veterinary pathologist at the National Zoological Park in Washington DC.

The scientists don't yet know if the fungus is the primary cause of death, or is killing animals weakened by other factors, such as ultraviolet radiation penetrating the atmosphere due to the thinned ozone layer or agricultural chemicals. "Many factors could be at work, but the fungus is probably right up there," says Pessier.

Nobody knows where the fungus came from, or how it is spread (see below). It was first noticed by Don Nichols, a colleague of Pessier's at the zoo in Washington DC, in arroyo toads, Bufo microscaphus californicus, from a captive colony in California.

At first Nichols didn't recognize it as a fungus. Because infected skin contained a proliferation of round cells, rather than fungal filaments, Nichols thought it was a protozoan. Earl Green of the Maryland Animal Health Laborat
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44 171 331 2751
New Scientist
24-Jun-1998