Causal Agent:
Despite its name, Dientamoeba fragilis is not an ameba but a flagellate.  This protozoan parasite produces trophozoites; cysts have not been identified.  Infection may be either symptomatic or asymptomatic.

Life Cycle:

The complete life cycle of this parasite has not yet been determined, but assumptions were made based on clinical data.  To date, the cyst stage has not been identified in D. fragilis life cycle, and the trophozoite is the only stage found in stools of infected individuals .  D. fragilis is probably transmitted by fecal-oral route and transmission via helminth eggs (e.g., Ascaris, Enterobius spp.) has been postulated .  Trophozoites of D. fragilis have characteristically one or two nuclei (, ), and it is found in children complaining of intestinal (e.g., intermittent diarrhea, abdominal pain) and other symptoms (e.g., nausea, anorexia, fatigue, malaise, poor weight gain).

Geographic Distribution:
Worldwide.