Frog-killing fungus to be tackled in the wild

Issue 2684 of New Scientist magazine 28 Nov 08;

A FUNGAL disease is decimating amphibian populations around the world, and so far the only way to save a species at risk is to remove individuals from the wild. Is it time to try taking out the disease as well?

So far the majority of amphibian conservation efforts have focused on identifying species at high risk of extinction, and establishing captive breeding programmes in biosecure units where they will be protected from Batrachochytrium dendrobatidis (Bd), the chytrid fungus that is responsible for the devastating scourge.

"The immediate response has been the right one: to get species that are at risk into captivity," says Trent Garner of the Institute of Zoology in London. However, he adds, "we're potentially missing out on some very important species" because, inevitably, some are prioritised over others.

Now an alternative strategy is emerging, which many had previously thought impossible: to reduce the amount of Bd in the wild, and perhaps even to enable amphibians to survive alongside it.

In lab experiments, Garner and colleagues have shown that it is possible to cure tadpoles infected with Bd by bathing them in the antifungal drug itraconazole for 5 minutes a day for seven days. "Even using extremely low doses, we showed that you can eliminate Bd from tadpoles," says Garner, who presented his results at a meeting on amphibian decline at the Zoological Society of London last week.

What's more, detailed inspection a month later showed the tadpoles had suffered none of the drug's possible side effects, which can include liver damage.

Early next year, Garner and his team will travel to Majorca, Spain, where Bd is taking its toll on the Majorcan midwife toad - currently ranked 55 on a list of the 100 amphibian species most at risk of extinction, according to the Zoological Society of London.

The team plans to remove midwife toad tadpoles from the clear limestone pools in which they live, and subject them to similar treatments, before releasing them back into the wild. Because Bd may still be present in the pools, Garner's team will experiment with how many tadpoles need to be treated, and how often, for the population to survive at viable levels. "The goal is mitigation, not elimination," says Garner. Since symptoms of the disease vary according to the amount of fungus amphibians are exposed to, such mitigation could make Bd infection less deadly and mean fewer new infections.

"It's a very ambitious experiment," says Richard Griffiths of the University of Kent in Canterbury, UK. He also warns that a different strategy may be needed to combat Bd in other parts of the world. Garner agrees that things get more complicated if, for instance, the number of species living in the habitat is large. His team also plans to build artificial ponds to investigate dosing more complex ecosystems than Majorca's with antifungal drugs.

Another option discussedat the meeting for protecting amphibian populations from Bd and other threats is to preserve their sperm and eggs, so that genetic diversity can be maintained as numbers dwindle. For example, since June, the Amphibian Ark project has been discussing the establishment of regional amphibian "biobanks".