Pregnancy test may lie behind deadly frog fungus
|
|
What do an old pregnancy test for women and a mysterious fungus that is killing frogs have in common?
Plenty, according to researchers at North-West University in South Africa, who believe they have traced the spread of the killer fungus to trade in the African clawed frog, used for decades in a bizarre but effective way of determining pregnancy.
“We think we have traced the origin of the spread of the amphibian chytrid fungus to the ‘frog’ pregnancy test for women, which was widely used from the 1930s to the 1960s,” said Che Weldon, a zoologist at North-West University who has been researching the phenomenon.
That test involved taking the urine of a woman and injecting it into an African clawed frog. If the woman was pregnant the hormones in her urine would stimulate ovulation in the frog and it would spawn within a matter of hours.
The species was exported to labs around the world in huge quantities from South Africa from the 1930s—the decade in which Weldon has traced the first recorded case of the fungus by examining preserved frogs in museum collections.
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 of the fungus recorded outside South Africa was in 1961 in Quebec, Canada.
Adding 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.
However, it remains unclear if its roots are in southern Africa or elsewhere on the continent.
“Frogs here for the most part are resistant to it. Some do succumb to it but we have not witnessed the mass die-offs experienced elsewhere,” said Weldon.
The African clawed frog itself shows no clinical symptoms of the disease, which means it is the perfect vector: a carrier which does not die from the fungus.
HOPPING MAD
However, other species in southern Africa are not resistant, although there are none of the die-offs recorded in other parts of the world.
The clinical signs are obvious to experts: crazy frogs.
“The symptoms are neurological and seem to affect their behavior,” said Weldon.
River frogs, for example, are found far above the water level in plants and even high up in trees. Nocturnal species come out in daylight.
“This river frog is infected. I picked it up a meter high in a fern,” said North-West University zoologist Louis du Preez as he lifted the lid of a plastic container to reveal a small, strikingly green frog.
Frogs infected with the fungus also display an excessive shedding of their skin.
The fungus is having a devastating impact on frog populations around the world, lending a sense of urgency to the research being done here.
“You have to go the origin of the disease. The idea of ‘out of Africa’ is still a hypothesis but it has a lot of support,” said du Preez.
Another team of researchers said in early January that the fungus had been aggravated by global warming and has killed entire frog populations in Central and South America.
Du Preez said it had been detected in the Americas, Africa, Australia and Europe but, so far, not Asia.
“It probably hasn’t been found in Asia yet simply because scientists have not made a concerted effort to find it there,” he said.
About a third of the 5,743 known species of frogs, toads and other amphibians are classified as threatened, according to the Global Amphibian Assessment.
Up to 167 species may already be extinct and another 113 species have not been seen in recent years. Habitat loss is a major threat but species have also died off in pristine environments, pointing to other causes such as the fungus.
“We fear that species are even being wiped out before they have been described by science,” said Du Preez.
The team is off this month to the Indian Ocean island of Madagascar to see if the fungus is present there.
Madagascar, famed for its weird and wonderful wildlife, is home to about 250 frog species, all but one of which are found nowhere else, according to du Preez.
The ecological stakes are high.
“Amphibians are right in the center of the food chain. They keep insect numbers down and serve as food themselves for many species, including wading birds, reptiles and even fish,” said Weldon.
“If you remove that link you remove an enormous flow of energy from the ecosystem,” he said.
Print Version
Tell-a-Friend comments powered by Disqus
