Cure found for killer 'Frog Fungus'
About a third of all amphibian species are threatened with extinction; 122 species have disappeared since 1980 .The biggest threat is a disease, chytridiomycosis, caused by a pathogenic fungus, Batrachochytrium dendrobatidis. First identified just eight years ago, B. dendrobatidis is responsible for the decline of many amphibian populations in the Americas, Australia and Europe and has been recently detected in Japan. In 2001 B. dendrobatidis was discovered during a dramatic decline of one of New Zealand's native frogs (Archey’s frog). This frog species is listed as Nationally Critical by the Department of Conservation, New Zealand . Global Action Plan
The global action plan includes investigation into drugs against Batrachochytrium, though these have been considered to be a long way off. There are few methods of treating captive frogs infected with Batrachochytrium and none to treat wild amphibian populations that are infected. To date, no treatments have been consistently effective across species.
Captive breeding programmes, planned as the only way to preserve threatened species until the chytrid can be beaten, remain vulnerable to the introduction of Batrachochytrium. A protocol to treat infected captive frogs would be an asset in these breeding programmes, including for situations where potentially infected animals are to be relocated to new environments. However, many species cannot be bred in captivity and their continued existence may rely on the removal of Batrachochytrium from their environment.
B. dendrobatidis is a member of an unusual, ancient kingdom of fungi (Chytridomycota), quite unlike the more familiar yeasts and moulds. Chytrids spread through water via motile zoospores. B. dendrobatidis is the only chytrid known to infect vertebrates; it can infect a wide range of amphibian species, although with varying ability to create disease (that is, some amphibian species carry the organism but do not exhibit chytridiomycosis).
Cure discovered
An extensive screen of available antibiotics and antifungals for their activity against B. dendrobatidis in vitro have been trialled. Amongst these compounds is one (chloramphenicol) that is lethal to chytrids in vitro (after 5 days) and apparently non-toxic to amphibians. It was shown that this protocol cures experimentally infected Brown Tree frog and Southern Bell frog, (IUCN status is endangered); both are species introduced to New Zealand from Australia.
While there is still a long way to go, this therapeutic protocol will provide an invaluable tool for captive breeding and/or relocation programmes. Obviously most frogs don't live in captivity, and many frogs have never bred in captivity, so there is still a very, very long way to go, but this is a vital first step.
2008 declared Year of the Frog
