Fatal frog fungal disease figured out

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Electrolyte imbalance stops amphibians' hearts.

Emma Marris
frogFrogs are suffering from a fatal fungal infection.Vance T. Vredenburg/SFSU

A fungal infection that is killing amphibians around the world acts by disrupting the flow of electrolytes across their skin, ultimately causing heart failure. The discovery is helping to raise hopes that a treatment for the infection could one day be given to amphibians in the wild.

Batrachochytrium dendrobatidis, a kind of chytrid fungus that causes the skin disease chytridiomycosis in amphibians, was likely spread around the world by the South African clawed frog (Xenopus laevis) in the 1930s and 1940s, when the frog was widely used as a pregnancy test. A pregnant woman's urine, injected under the frog's skin, would contain sufficient hormones to make the animal ovulate.

But although the South African clawed frog seems to have immunity to the disease, many other amphibians are not so lucky. According to one study led by chytrid expert Karen Lips of the University of Maryland in College Park, chytridiomycosis can kill 80% of amphibians in one year in an area with cool, moist conditions.1 Until now, no one was sure exactly how the fungus killed its victim; some researchers thought that it might secrete a poison.

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http://www.nature.com/news/2009/091022/full/news.2009.1031.html

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1. Being warm-blooded helps protect us mammals from this stuff

http://www.medicalnewstoday.com/articles/167652.php

The fact that they eat a lot - and often - may explain why most people and other mammals are protected from the majority of fungal pathogens, according to research from Albert Einstein College of Medicine of Yeshiva University.

The research, published in the Journal of Infectious Diseases, showed that the elevated body temperature of mammals - the familiar 98.6o F or 37o C in people - is too high for the vast majority of potential fungal invaders to survive. . . .

There are roughly 1.5 million fungal species. Of these, only a few hundred are pathogenic to mammals. Fungal infections in people are often the result of an impaired immune function. By contrast, an estimated 270,000 fungal species are pathogenic to plants and 50,000 species infect insects. Frogs and other amphibians are prone to fungal pathogens, one of which, chytridiomycosis, is currently raging through frogs worldwide. Fungi are also important in the decomposition of plants. . . .

The results of the study, he added, could help explain why mammals maintain a seemingly energy-wasteful lifestyle requiring a great deal of food. By contrast, reptiles need only eat once a day or even less often. "The payoff, however, may be that mammals are much more resistant to soil and plant-borne fungal pathogens than are reptiles and other cold-blooded vertebrates," said Dr. Casadevall.