By Kim Griggs
Science reporter, Wellington
New Zealand scientists have found what appears to be a cure for the disease that is responsible for wiping out many of the world's frog populations.
The disease has had a devastating impact on frog populations (Conservation Int/D.Church)
Chloramphenicol, currently used as an eye ointment for humans, may be a lifesaver for the amphibians, they say.
The researchers found frogs bathed in the solution became resistant to the killer disease, chytridiomycosis.
The fungal disease has been blamed for the extinction of one-third of the 120 species lost since 1980.
Fearful that chytridiomycosis might wipe out New Zealand's critically endangered Archey's frog (Leiopelma archeyi), the researchers have been hunting for a compound that would kill off the disease's trigger, the fungus Batrachochytrium dendrobatidis.
They tested the chloramphenicol candidate on two species introduced to New Zealand from Australia: the brown tree frog (Litoria ewingii) and the southern bell frog (L. raniformis).
"We found that we could cure them completely of chytrids," said Phil Bishop from the University of Otago.
"And even when they were really sick in the control group, we managed to bring them back almost from the dead."
"You could put them on their back and they just wouldn't right themselves, they would just lie there. You could then treat them with chloramphenicol and they would come right," Dr Bishop explained.
But the Zoological Society of London (ZSL) expressed caution at the news. Wildlife epidemiologist Dr Trent Garner said there would be reluctance to take up chloramphenicol as a solution, certainly in Europe and North America, because of the chemical's link to harmful side-effects in humans.
The NZ researchers tried using chloramphenicol as both an ointment, applied to the frogs' backs, and as a solution.
They found that placing the animals in the solution delivered the best results. The team has admitted it was surprised by the outcome.
"You don't usually expect antibiotics to do anything to fungi at all. And it does. We don't understand why it does, but it does," said Russell Poulter.
Professor Poulter, the molecular biologist who hunted down chloramphenicol, added: "It's also got the great advantage that it's incredibly cheap."
WHAT ARE AMPHIBIANS?
Group includes frogs, toads, salamanders and caecilians
First true amphibians evolved about 250m years ago
Adapted to many different aquatic and terrestrial habitats
Present today on every continent except Antarctica
Undergo metamorphosis, from larvae to adults
The scientists are now making their research widely known ahead of formal publication in a science journal because of the pressing need for a safe and effective treatment for the chytrid disease.
The blow that chytrid has dealt to the frog population is already immense.
The disease has probably accounted for one-third of all the losses in amphibian species to date, says Professor Rick Speare, an expert in amphibian diseases who works with the University of Otago's frog research group.
These losses are huge - and this is in addition to other threats such as habitat destruction, climate change, pollution and hunting.
Since 1980, more than 120 amphibian species have disappeared; and according to the World Association of Zoos and Aquariums, in the near future many more species are in danger of vanishing.
"We are losing an awful lot of these creatures now and if we don't do something intelligent, then we're going to lose an awful lot more," said Professor Poulter.
But a hopeful finding is that the introduced frogs that have been infected with chytrids are now more resistant to further infections.
"We haven't quite understood how that could happen," said Dr Bishop. "It might be a natural thing; if a frog survives a chytrid infection then it is resistant when it gets attacked again."
The researchers believe that zoos now will have more options, either to be able to control an outbreak or to rescue infected frogs from the wild, knowing that they can be cured.
The next challenge the research team has set itself is to find a treatment that will work in the wild.
"I would really feel quite satisfied if we could say, 10 years from now, that you have to be careful walking around [Australia's] Kosiuszko National Park or you might tread on a corroboree frog because they're all over the place," said Professor Poulter. "I would take real satisfaction from that."
However, just how widely chloramphenicol might be adopted is open to debate. EU and US authorities are concerned the drug may cause aplastic anaemia in humans. "It is a banned substance; in particular, it is controlled where it comes into contact with food sources," commented Dr Garner from ZSL.
"There are other antifungals that are being piloted and some are looking promising. Treating infection in amphibians is possible, but determining if there are any side-effects takes time. Also, how you apply an antifungal at the individual, the population and the species level is a whole set of questions which needs to be addressed."