Researchers at South Africa's North-West University think they have traced the spread of the chytrid fungus to a long-standing trade in the African clawed frog.
The frog was used as part of an unusual but effective way of determining pregnancy from the 1930s to the 1960s. The test involved taking the urine of a woman and injecting it into the frog. If the woman was pregnant the hormones in her urine would stimulate ovulation in the frog and within a matter of hours, it would spawn.
Huge numbers of African clawed frogs were exported from South Africa to laboratories carrying out the test all over the world, beginning in the 1930s - the decade in which the first case of the fungus was recorded. They have been traced by examination of preserved frogs in museum collections by Che Weldon, a zoologist at North-West University.
Mr Weldon has researched the spread of the fungus, seen in the Americas, Africa, Australia and Europe, and he thinks the trade could have been responsible. Some of the exported frogs were released or escaped into the wild where it is believed they spread the fungus, which can move quickly through a water system and can jump from one frog species to another. The first case recorded outside South Africa was in Quebec, Canada, in 1961.
Last month, an international team of researchers reported that global warming was helping to spread the deadly skin infection and was triggering the decline of hundreds of species of frogs and toads. It is thought that the average temperatures of many tropical regions, rich in frog and toad species, have shifted to become perfect for the growth of the fungus.
Scientists believe the chytrid fungus is behind the disappearance of the golden toad of Costa Rica, and at least 67 per cent of the 110 species of harlequin frogs from South and Central America over the past 17 years.
What is thought to add weight to the case for an African origin is the fact that the fungus is widespread in southern Africa, but frogs in the region appear to have developed a resistance to it. Mr Weldon said: "Some do succumb, but we have not witnessed the mass die-offs experienced elsewhere."
Infected frogs show an excessive shedding of their skin, and exhibit strange behaviour. Nocturnal species come out in daylight, and river frogs are found above water level among plants.
Last year, it was announced that the chytrid fungus had been found in a colony of escaped American bullfrogs in the south-east of England. The Government's wildlife watchdog, English Nature, has removed more than 11,000 of the infected colony, but it is possible the fungus has infected native British amphibians. Tests are being carried out to discover if the disease has become established in the UK.Reuse content