Dientamoeba fragilis Infection

[Dientamoeba fragilis]

Causal Agents

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 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. 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 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).

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.

Geographic Distribution

Worldwide.

Clinical Presentation

Symptoms that have been associated with infection include diarrhea, abdominal pain, anorexia, nausea, vomiting, fatigue, and weight loss.

Dientamoeba fragilis binucleate trophozoites stained with trichrome

Dientamoeba fragilis is a flagellate that must be morphologically differentiated from the small nonpathogenic amebas. Dientamoeba fragilis has no cyst stage, and its trophozoites measure 5 to 15 µm. The flagella is not usually evident and the pseudopodia are angular to broad-lobed and transparent. While most trophozoites are typically binucleate, some have only one nucleus.

Figure A: Binucleate form of a trophozoite of D. fragilis, stained with trichrome.

Figure B: Binucleate form of a trophozoite of D. fragilis, stained with trichrome.

Figure E: Binucleate form of a trophozoite of D. fragilis, stained with trichrome.

Figure D: Binucleate form of a trophozoite of D. fragilis, stained with trichrome.

Figure C: Binucleate form of a trophozoite of D. fragilis, stained with trichrome.

Figure F: Binucleate form of trophozoites of D. fragilis, stained with trichrome. A cyst-like form of Blastocystis hominis lies to the left of the D. fragilis.

Dientamoeba fragilis uninucleate trophozoites stained with trichrome.

Dientamoeba fragilis is a flagellate that must be morphologically differentiated from the small nonpathogenic amebas. Dientamoeba fragilis has no cyst stage, and its trophozoites measure 5 to 15 µm. The flagella is not usually evident and the pseudopodia are angular to broad-lobed and transparent. While most trophozoites are typically binucleate, some have only one nucleus.

Figure A:Uninucleate form of a trophozoite of D. fragilis, stained with trichrome.

Figure B: Uninucleate form of a trophozoite of D. fragilis, stained with trichrome.

Figure C: Uninucleate form of a trophozoite of D. fragilis, stained with trichrome.

Figure D: Binucleate and uninucleate forms of trophozoites of D. fragilis, stained with trichrome.

Laboratory Diagnosis

Infection is diagnosed through detection of trophozoites in permanently stained fecal smears (e.g., trichrome). This parasite is not detectable by stool concentration methods. Dientamoeba fragilis trophozoites can be easily overlooked because they are pale-staining and their nuclei may resemble those of Endolimax nana or Entamoeba hartmanni.

Morphology

More on: Morphologic comparison with other intestinal parasites.

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.

DPDx - Laboratory Identification of Parasitic Diseases of Public Health Concern

Dientamoeba fragilis Infection

Causal Agents

Life Cycle

Geographic Distribution

Clinical Presentation

Dientamoeba fragilis binucleate trophozoites stained with trichrome

Dientamoeba fragilis uninucleate trophozoites stained with trichrome.

Laboratory Diagnosis

Morphology

Treatment Information

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Dientamoeba fragilis Infection

Causal Agents

Life Cycle

Geographic Distribution

Clinical Presentation

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