出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/04/19 15:08:38」(JST)
| Dientamoeba fragilis | |
|---|---|
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Excavata |
| Phylum: | Metamonada |
| Class: | Parabasalia |
| Order: | Trichomonadida |
| Family: | Monocercomonadidae |
| Genus: | Dientamoeba |
| Species: | D. fragilis |
| Binomial name | |
| Dientamoeba fragilis |
|
Dientamoeba fragilis is a single-celled parasite found in the gastrointestinal tract of some humans, pigs and gorillas. It causes gastrointestinal upset in some people, but not in others.[1] It is an important cause of travellers diarrhoea, chronic diarrhoea, fatigue and, in children, failure to thrive.
It was first described in 1918.[2]
Infection with Dientamoeba fragilis is called Dientamoebiasis and is associated variously with symptoms of abdominal pain, diarrhea, weight loss, and fever.
In one study, Dientamoeba fragilis was identified in 0.9% of patients observed. Its coincidence with Enterobiasis has been reported.[3]
Dientamoeba fragilis is a type of trichomonad. Trichomonads are flagellated organisms but D. fragilis lacks flagella,[4] having secondarily 'lost' them over evolutionary time. Thus, it is an amoeba of flagellate ancestry. In point of ultrastructural and antigenic view, Dientamoeba is reclassified as a flagellate.
The life cycle of this parasite has not yet been completely determined, but some assumptions have been made based on clinical data. Recently a cyst stage has been reported,[5] although it is yet to be independently confirmed. If true, D. fragilis is probably transmitted by the fecal-oral route. Prior to the report of this cyst stage in the life cycle of Dientamoeba it was postulated that transmission occurred via helminth eggs (e.g., Ascaris, Enterobius spp.). The rationale for this suggestion was that D. fragilis is closely related to the turkey parasite Histomonas, which is known to be transmitted via the eggs of the helminth Heterakis.
Dientamoeba fragilis replicates by binary fission and moves by pseudopodia. D. fragilis feeds by phagocytosis. The cytoplasm typically contains numerous food vacuoles that contain ingested debris, including bacteria. Waste materials are eliminated from the cell through digestive vacuoles by exocytosis. D. fragilis possesses some flagellate characteristics. In the binucleate form there is a spindle structure located between the nuclei, which stems from certain polar configurations adjacent to a nucleus—these configurations appear to be homologous to hypermastigotes’ atractophores. There is a complex Golgi apparatus; the nuclear structure of D. fragilis is more similar to that of flagellated trichomonads than to that of Entamoeba. Also notable is the presence of hydrogenosomes, which are also a characteristic of other trichomonads.[6]
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| リンク元 | 「二核アメーバ」 |
| 関連記事 | 「Dientamoeba」 |