THE entire population of the world's frogs and other amphibians could be wiped out by a deadly fungus within three decades, experts have warned.
Biologists say a strain of the chytrid virus that kills frogs, toads, newts and other amphibians could spell the biggest mass extinction since the dinosaurs.
Species resistant to it, including the cane toad, are spreading it throughout the world.
The chytrid fungus, Batrachochytrium dendrobatidis, infects all kinds of amphibians and causes the fatal disease chytridiomycosis.
Iain Stephen, of London Zoo, said: "Frogs, toads, newts, salamanders and caecilians, which are limbless, almost eel-like amphibians, are all under threat.
"There are 6,000 species of amphibians in the world and over two-thirds of them are in decline," he said. "That's a higher percentage than any other animal group.
"It's the biggest decline taking place on the planet. Over the next 20 or 30 years we could be talking about the biggest mass extinction since the dinosaurs."
In the past few years more than 100 species of frogs have become extinct. In Scotland it could be the end of much-loved creatures often seen in the garden, such as the common toad.
It is thought amphibians catch the disease from contact with each other, and from water containing the deadly spores. Their skin becomes discoloured and peels, they grow sluggish and lose their appetite.
Already the disease has been found in Cumbria and Kent, and there are fears it is only a matter of time before it reaches Scotland. Lucy Benyon, the wildlife information officer at amphibian charity Froglife, said: "It has wiped out so many species already that it's possible it could wipe out all of them."
She thinks the fungus could also have an impact on birds and animals that eat frog spawn, and the populations of insects kept in check by amphibians.
"They are quite important in the food chain," said Ms Benyon. "Amphibians produce so many eggs and spawn is because lots of them get eaten by other animals. It would have a knock-on effect on the ecosystem."
Ms Benyon said in Scotland and the rest of the UK toads and newts will be most at risk, and she encouraged members of the public to look out for large groups of dead amphibians.
"If there are lots of dead animals in one place with skin problems, contact us," she said. "If there are just one or two it is usually nothing to worry about."
Scientists first noticed the alarming number of amphibians under threat about 15 years ago. But it was not until the late 1990s that it was discovered the chytrid fungus was to blame.
It is believed the deadly fungus originated in South Africa, and spores were then spread by the commercial trade in African clawed frogs, which were used as an early pregnancy test.
Some notorious pest species, including the cane toad, American bullfrog and African clawed frog, have resistance and have been spreading it throughout the world.
The trade in American bullfrogs for frogs' legs, and the demand for amphibians as pets, is also helping to spread the disease. More than 3,000 species are thought to be in trouble already, with 165 now extinct.
Mr Stephen said: "The disease is very rapid. You can have a total die-off within weeks of its arrival. The introduction of the cane toad was terrible for Australia. Suddenly they had this massive toad eating all the amphibians and introducing chytrid to the environment.
"Any frogs which weren't eaten ended up with the disease."
Although chytridiomycosis can be treated easily in a controlled environment with fungicide, combating it in the wild is almost impossible.
"You can't go around spraying the forest with fungicide," said Mr Stephen. "It's a pretty dire situation."
He thinks rescue programmes in zoos are the best option. "Zoos have an important part to play to stop the extinction. All zoos are working out how to accommodate and care for a much bigger number of amphibians than usual."
Pregnancy-test frogsTHE disease threatening amphibians worldwide may stem back to the use of frogs as pregnancy tests.
Live female frogs were used widely in Europe, Australasia and North America in the 1930s to see if women were pregnant. A sample of the woman's urine was injected under the frog's skin. If she was pregnant, a hormone in her urine caused the frog to ovulate. Scientists believe African frogs exported for use as tests could have carried the fungal disease.
The full article contains 760 words and appears in The Scotsman newspaper.
