April 15, 2009


 New guidelines intended to guard amphibians against deadly fungus

Posted April 1, 2009 

Efforts are under way to protect captive amphibians from a deadly fungus threatening numerous endangered species.

The chytrid fungus, discovered in the mid-1990s and associated with declines in amphibian populations worldwide, notably in Central America and Australia, is spreading quickly in the wild—most likely as a consequence of human activity. 

Chytrid fungus has so devastated the golden Panamanian frog that it is nearly extinct in the wild.

In February, 25 of the world's leading amphibian veterinarians, disease researchers, and husbandry specialists gathered at San Diego Zoo for a three-day conference to write a comprehensive manual for controlling and combating diseases in amphibian survival assurance colonies. Survival assurance colonies have been formed in zoos throughout the world to preserve amphibian species that are rapidly facing extinction.

The assembled experts hope not only to safeguard amphibian collections from chytrid and other pathogens but also to preserve rare and endangered frogs so that they may one day be released into their native habitats.

Chytrid fungal disease causes the infected amphibian's skin to thicken, interfering with its ability to absorb water and electrolytes. When the fungus spreads to an area with a highly susceptible species, the results are devastating, according to Dr. Allan P. Pessier, a veterinary pathologist and researcher at the San Diego Zoo.

"There's actually good documented evidence that chytrid fungus will move into a naive population of frogs and quickly result in this horrific picture of wiping out these local populations," Dr. Pessier said.

Amphibians in the wild already are in danger of extinction, attributable to any number of factors, including habitat loss, the pet trade, and climate change. The current global decline in amphibians is being compared in magnitude to the extinction rate of the dinosaurs, according to Dr. Pessier.

Zoo Atlanta's curator of herpetology, Joseph R. Mendelson, PhD, said dozens of frog species have already vanished because of chytrid. In environments where the fungus thrives, it can kill 80 percent of the native amphibians within months, according to Dr. Mendelson, who added that, in the wild, chytrid is unstoppable and untreatable.

"Chytrid fungus is doing things that diseases don't normally do; namely, it's driving species directly to extinction. That doesn't happen in a normal, healthy world," he said.

The first known record of chytrid infection in frogs was in the African clawed frog, which is commonly sold in pet stores and used for research worldwide.

Chytrid is a sporadic problem in U.S. zoo collections and is also a concern for species reintroduction programs because of the potential to release infected frogs back into the wild, according to Dr. Pessier.

For these reasons, the San Diego Zoo and Zoo Atlanta, with financial support from the Institute of Museum and Library Services, brought together amphibian specialists from the United States, United Kingdom, and Australia to codify disease control protocols for captive amphibians.

Included in the manual is information on setting up a biosecure amphibian facility, diagnosing and treating chytrid fungus in a collection, and disease screening necessary to release healthy animals back in the wild. The manual, which will be provided free of charge, is currently being edited and will be reviewed prior to its anticipated release in fall 2009.

In addition, the grant from the Institute of Museum and Library Services has made it possible for the San Diego Zoo to offer the nation's zoos and aquariums low-cost diagnostic testing for amphibian diseases. Additional laboratory staff have been hired, and testing is already under way, Dr. Pessier said.