Chytridiomycosis

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A chytrid-infected frog

Chytridiomycosis in Atelopus varius - two sporangia containing numerous zoospores are visible

Chytridiomycosis is an infectious disease of amphibians, caused by the chytrid fungus Batrachochytrium dendrobatidis. Chytridiomycosis has been linked to dramatic population declines or even extinctions of amphibian species in western North America, Central America, South America, and eastern Australia. There is no effective measure for control of the disease in wild populations. The disease is contributing to a worldwide decline in amphibian populations, a worldwide decline of species that apparently has affected 30% of the amphibian species of the world^[1].

Although some declines have been credited to the fungus B. dendrobatidis, there are species that resist the infection and some reports have found that some populations can survive with a low level of persistence of the disease^[2]. In addition, most of the laboratory studies are not ecologically-relevant, which makes it difficult to take their conclusions to the field.

The oldest reports of infection of Batrachochytrium were from African clawed frogs of the genus Xenopus. Because Xenopus has been widely transported around the world, it is one potential vector for transmission of B. dendrobatidis.^[3] Other studies, however, suggest that B. dendrobatidis has been present in North and Central America for decades. It is still not clear if it is a new emergent pathogen or if it is an old pathogen with recently increased virulence.

Laboratory studies suggest that the fungus performs poorly at high temperatures^[4], and that exposure of infected frogs to high temperatures will kill the fungus^[5]. This may explain why chytridiomycosis occurs primarily in cool regions, like mountain chains.

[edit] Notes

^ Stuart, S. N., J. S. Chanson, et al. (2004). "Status and trends of amphibian declines and extinctions worldwide." Science 306: 1783-1786.
^ Retallick, R. W. R., H. McCallum, et al. (2004). "Endemic Infection of the Amphibian Chytrid Fungus in a Frog Community Post-Decline." PLoS Biology 2(11): e351.
^ Origin of Amphibian Chytrid Fungus | CDC EID
^ Berger, L., R. Speare, et al. (2004). "Effect of season and temperature on mortality in amphibians due to chytridiomycosis." Australian Veterinary Journal 82: 31-36.
^ Woodhams, D. C., R. A. Alford, et al. (2003). "Emerging disease of amphibians cured by elevated body temperature." Diseases of aquatic organisms 55: 65-67.