A skin fungus known as “Bd” is killing off amphibians the world over. Hikers may be inadvertently helping spread the microorganism, which scientists believe may be a hybrid of two less dangerous fungi. In Europe, Bd already affects 20 different amphibian
Amphibians – and hikers – beware. A fungus that attacks delicate amphibian skin is coursing through the world like wildfire, threatening thousands of species of frogs, toads, newts and salamanders.
Focusing their research on frogs in the southern Sierra Nevada mountains in the United States, a team of scientists at the University of California in Berkeley found that the fungus – known as Batrachochytrium dendrobatidis (Bd) – begins by disrupting the animals' natural balance of potassium and sodium. The amphibians become progressively lethargic and stop eating until their hearts come to a halt. The team, headed by Jamie Voyles, published their findings in the journal "PLoS ONE."
The fungus first began proliferating in the Sierra Nevada in 2004. At first, only a few animals fell ill, but then the infection started spreading quickly to the point where frogs were dying en masse. By 2008, the area's frog population fell to just a quarter of its original size.
Around the globe, the fungus has already killed off 200 species of amphibian, say researchers at RACE, the European Bd monitoring project. As for Europe, the fungus was first spotted in Spain in 1999. It has now spread to Great Britain, Italy, Portugal, and Switzerland. More than 20 species of amphibians in these countries have been infected.
How can a single fungus endanger an entire class of animals, particularly one with the longest history among land vertebrates?
"It appears that the aggressive Bd lines are hybrids of two less dangerous forms brought together through the trade in exotic frogs," says Dirk Schmeller of the Paris-based Centre National de la Recherche Scientifique. Schmeller and his colleagues have tested various amphibian populations for their susceptibility to the Bd fungus. "Almost always, the hardest hit populations are amphibians that live at altitudes of over 1,000 meters."
Hikers are part of the problem
In Europe, amphibians living at lower altitudes are more resistant to Bd, although they can carry the fungus even if they are themselves unaffected by it. Human beings can be carriers as well, as researchers conducting a Europe-wide poll of hikers found. "Hikers seem to like amphibians a lot. Kids for example will pick one up, and maybe even bring it from one pond to another – and with it, the fungus," Schmeller explains.
Schmeller says that if hikers were more aware of the situation they could perhaps slow the spread of the fungus. "But of course various animals and birds also spread the fungus," he says. What is all the more annoying, he adds, is that there are ways to effectively combat the fungus.
"Bd can actually be stopped very simply with a solution of Itraconazole. But you have to keep using it," says Schmeller. "In field research on Mallorca we showed that frogs given an Itraconazole bath seven or eight times were freed of the fungus, but that they got in again after about two years. So the treatment exists. What's difficult, is treating amphibians in the wild."
Read the original story in German by Pia Heinemann
Photo – brian.gratwicke
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