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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:

Dientamoeba fragilis lifecycle

The complete life cycle of Dientamoeba fragilis has not yet been determined, and assumptions were made based on clinical data. Historically, this species was known only from the trophozoite stage in stools of infected individuals The number 1 . In 2014, cyst and precyst stages were described for the first time in clinical human specimens. These data are still considered preliminary and further testing should be done to validate the existence of this stage in the human host.
D. fragilis
is probably transmitted by fecal-oral route The number 2 and transmission via helminth eggs (e.g., Ascaris, Enterobius spp.) has been postulated The number 3 . Trophozoites of D. fragilis have characteristically one or two nuclei ( The number 1 , The number 4 ), 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).

Reference: Stark D, Garcia LS, Barratt JLN, Phillips O, Roberts T, Marriot D, Harkness J, Ellis JT. Description of Dientamoeba fragilis cyst and precystic forms from human samples. Journ Clin Micro. 2014; 52: 2680-2683.

Life cycle image and information courtesy of DPDx.