|
''Cyclospora cayetanensis'' is a protozoan that causes disease in humans, and perhaps primates. It has been linked in the United States to fecally contaminated imported produce, and was virtually unknown before about 1990, but has been on the rise since. The health risk associated with the disease is usually confined to adult foreigners visiting regions where the species is endemic and acquiring the infection, which is why ''C. cayetanensis'' has been labeled as causing "traveler's diarrhea." This species was placed in the ''Cyclospora'' genus because of the spherical shape of its sporocysts. The species name refers to the Cayetano Heredia University in Lima, Peru, where early epidemiological and taxonomic work was done.〔(【引用サイトリンク】title=Cyclospora cayetanensis )〕 ==Characterization== ''Cyclospora cayetanensis'' is an apicomplexan, cyst-forming coccidian protozoan that causes a self-limiting diarrhea. In terms of morphology, ''C. cayetanensis'' has spherical oocysts that are between 7.5 and 10 micrometers in diameter that also have a 50-nanometer-thick wall with an outer threadlike coat that has been called a wrinkle by some researchers. The only hosts for ''C. cayentanensis'' are humans. The protozoan lives out its lifecycle intracellularly within the host’s epithelial cells and gastrointestinal tract. Infection is transmitted through the fecal-oral route, and begins when a person ingests oocysts in fecally contaminated food or water. Various chemicals in the host's gastrointestinal tract cause the oocysts to excyst and release sporozoites; generally, two are observed per oocyst. After these sporozoites invade the epithelial cells, they undergo merogony, a form of asexual reproduction that results in many daughter merozoites. These daughter cells may either infect new host cells and initiate yet another round of merogony or take on a sexual track via gametogony: Daughter merozoites become male macrogamonts — which form many microgametes — and female macrogamonts. After fertilization has occurred via male microgamete fusion with female macrogamont, the zygote matures into an oocyst and ruptures the host cell, from which point it is passed with the stool. The oocysts that are passed are not, however, immediately infectious. Sporulation can take from one to several weeks, meaning person-to-person transmission is not a likely problem. This differentiates ''C. cayentanensis'' from ''Cryptosporidium parvum'' — a closely related organism that causes a similar disease — since ''C. parvum'' oocysts are immediately infectious upon release from the host. 〔()〕 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「Cyclospora cayetanensis」の詳細全文を読む スポンサード リンク
|