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''Blastocystis'' is a genus of single-celled protozoan parasites belonging to a group of organisms known as the Stramenopiles (also called Heterokonts) that includes algae, diatoms, and water molds. Blastocystis comprises several species, living in the gastrointestinal tracts of species as diverse as humans, farm animals, birds, rodents, reptiles, amphibians, fish, and cockroaches. ''Blastocystis'' exhibits low host specificity, and many different species of ''Blastocystis'' can infect humans and by current convention, any of these species would be identified as Blastocystis hominis if they were identified in a human. These have a widespread geographic distribution and are found at a rate of 5-10% in most developed countries, and a rate of up to 50% in less developed areas. High rates of infection are also found in individuals in developed countries who work with animals. Although the role of ''Blastocystis hominis'' in human disease is often referred to as controversial, a systematic survey of research studies conducted by 11 infectious disease specialists from nine countries, found that over 95% of papers published in the last 10 years identified it as causing illness in immunocompetent individuals. The paper attributed confusion over pathogenicity to the existence of asymptomatic carriers, a phenomenon the study noted is common to all gastrointestinal protozoa.〔 ==Classification== The appropriate classification of ''Blastocystis'' has only recently been resolved. The original description of ''Blastocystis'' was as a yeast due to its yeast-like glistening appearance in fresh wet mounts and the absence of pseudopodia and locomotion. This was then contradicted by Zierdt,〔Perez-Cordon, G. et al. (Finding of ''Blastocystis'' sp. in bivalves of the genus ''Donax'' ). ''Rev. peru biol.'' 2007, vol. 14, n.2, pp. 301-302.〕 who reclassified it under subphylum Sporozoa (and later in Sarcodina), based on some distinctive protistan features of the ''Blastocystis'' cell, such as the presence of nuclei, smooth and rough endoplasmic reticulum, Golgi complex, and mitochondrion-like organelles. Its sensitivity to antiprotozoal drugs and its inability to grow on fungal media further indicated that it was a protozoan. However, major revisions were made to its classification. An analysis of gene sequences was performed in 1996, which placed it into the group Stramenopiles. Other Stramenopiles include brown algae, mildew, diatoms, the organism that caused the Irish potato famine, and the organism responsible for Sudden oak death disease. However, the position of ''Blastocystis'' within the stramenopiles remains enigmatic. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Blastocystis」の詳細全文を読む スポンサード リンク
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