30 October 2007

A cure for the amphibian plague?

By
Comos Online
A New Zealand team has successfully used a human eye ointment to cure frogs of the chytrid skin fungus that is devastating global amphibian populations.
A cure for the amphibian plague?

Back from the brink: Archey's frogs develop in a gelatinous capsule and skip the tadpole stage, here the young frogs are carried on their father's back. The University of Otago team developed the chytrid treatment in an effort to protect the species. Credit: NZFROG/Rod Morris

WELLINGTON: A New Zealand team has successfully used a human eye ointment to cure frogs of the chytrid skin fungus that is devastating global amphibian populations.

With around half of the world’s amphibian species now endangered from a mix of the disease, climate change and habitat destruction, the breakthrough may offer a ray of hope to conservation biologists.

Developed at the University of Otago, in Dunedin, the treatment uses chloramphenicol, an antibiotic eye ointment. It is, “the best in the world,” for treating afflicted amphibians commented Rick Speare an expert on the fungus at James Cook University in Townsville, Australia.

Antibiotic ointment

The Otago researchers, with whom Speare collaborates, have successfully treated two different species of frogs with a solution of the antibiotic and completely rid them of infection with the Batrachochytrium dendrobatidis fungus.

Led by biologist Phil Bishop, the team were concerned that the fungus would drive New Zealand’s critically endangered Archey’s frog (Leiopelma archeyi) to extinction, so they set out to find a drug that might mitigate the infection.

Subsequent testing with a variety of compounds revealed that chloramphenicol was able to cure even the sickest individuals of the Brown Tree frog (Litoria ewingii) and the Southern Bell frog (L. raniformis), both invasive species from Australia, that it was tested on.

Prior to treatment “you could put them on their back and they just wouldn’t right themselves, they would just lie there,” said Bishop. But “you could then treat them with chloramphenicol and they would come right.”

Surprise success

The researchers have admitted surprise that the new ad-hoc treatment is so successful. “You don’t usually expect antibacterial antibiotics to do anything to fungi at all. And it does. We don’t understand why it does, but it does,” said molecular biologist and Otago team member Russell Poulter.

The team had been hunting for a compound that would kill chytrids but the choice of chloramphenicol was a lucky break. “When you grow chytrids in the laboratory, you put an antibiotic on the agar plate to make sure all the bacteria die,” explained Bishop, “and what [Russell Poulter] found was that when he used this chloramphenicol it killed the chytrid as well,­ so nothing grew.”

Another treatment for chytrid-infected frogs has been itraconazole, an antifungal antibiotic, but its use has not been without concerns. Itraconazole has been found to be highly toxic to the tadpoles of an Australian ground-dwelling amphibian, the great barred frog (Mixophyes fasciolatus). To date, no treatments have been consistently effective across species.

Though further research is required to confirm the effects of chloramphenicol across more species of frogs, the researchers have made their findings known ahead of a peer-reviewed publication in order to get the knowledge out to wildlife biologists as soon as possible.

“It will certainly be very handy [for infected frogs in captivity],” said Speare, and “if you’ve got a population of frogs that’s infected with chytrid and you want to take them out of the wild to establish a captive breeding population.”

Bringing endangered amphibians into ‘protective custody’ in zoos and aquariums, where they can be kept safe and used in breeding programs, is a key plank of an international action plan for amphibians developed by the leading conservationists. The new chytrid treatment should support those aims.

“The bottom line, if one was looking for it on a postcard,” said Poulter, “is that it is safe and it is effective.”

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