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Chytridiomycosis
Chytridiomycosis is an infectious disease of amphibians, caused by the chytrid ''Batrachochytrium dendrobatidis'', a nonhyphal zoosporic fungus. Chytridiomycosis has been linked to dramatic population declines or even extinctions of amphibian species in western North America, Central America, South America, eastern Australia, and Dominica and Montserrat in the Caribbean. Much of the New World is also at risk of the disease arriving within the coming years.〔 〕
The fungus is capable of causing sporadic deaths in some amphibian populations and 100% mortality in others. No effective measure is known for control of the disease in wild populations. Various clinical signs are seen by individuals affected by the disease. A number of options are possible for controlling this disease-causing fungus, though none has proved to be feasible on a large scale. The disease has been proposed as a contributing factor to a global decline in amphibian populations that apparently has affected about 30% of the amphibian species of the world.
==History==
The disease in its epizootic form was first discovered in 1993 in dead and dying frogs in Queensland, Australia. It had been present in the country since at least 1978 and is widespread across Australia. It is also found in Africa, the Americas, Europe, New Zealand, and Oceania. In Australia, Panama, and New Zealand, the fungus seemed to have suddenly ‘appeared’ and expanded its range at the same time frog numbers declined. However, it may simply be that the fungus occurs naturally and was only identified recently because it has become more virulent or more prevalent in the environment, or because host populations have become less resistant to the disease. The fungus has been detected in four areas of Australia—the east coast, Adelaide, south-west Western Australia and the Kimberley—and is probably present elsewhere.〔(【引用サイトリンク】url=http://www.environment.gov.au/biodiversity/invasive/publications/c-disease/pubs/c-disease.pdf )〕
The oldest documented occurrence of ''Batrachochytrium'' is from a Japanese giant salamander collected in 1902, although this strain of the fungus belongs to an endemic lineage that has not been implicated in any mass mortality events. The next known instance of a Bd-infected amphibian specimen of an African clawed frog (''Xenopus laevis'') collected in 1938, and this species also appears to be essentially unaffected by the disease, making it a suitable vector.〔Weldon; du Preez; Hyatt; Muller; and Speare (2004). ''(Origin of the Amphibian Chytrid Fungus. )'' Emerging Infectious Disease 10(12).〕 The first well-documented method of human pregnancy testing involved this species, and as a result, large-scale international trade in living African clawed frogs began more than 60 years ago.〔 If ''Batrachochytrium'' originated in Africa, it has been theorized that the African clawed frog was the vector of the initial spread out of the continent.〔 The earliest documented case of the disease chytridiomycosis was an American bullfrog (''Rana catesbeiana'') collected in 1978.〔 It is still not clear if it is a new emergent pathogen or if it is an old pathogen with recently increased virulence.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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