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Dientamoeba fragilis

Dientamoeba fragilis (Pathogen)

This organism belongs to the flagellates, is a true pathogen, and causes symptoms. There is both a trophozoite stage (usual size, 9-12 µm) and a cyst stage (usual size somewhat smaller than the trophozoite).

dient1 dient2
Trophozoites with single nucleus
Beginning to fragment (left), fragmented (right)

dient3 dient4 dient5
Trophozoites with two fragmented nuclei

Life Cycle:
Intestine, organisms passed in feces; trophozoites thought to be transmitted inside of helminth eggs (Ascaris lumbricoides, Enterobius vermicularis).

Fecal-oral transmission via trophozoite form; contaminated food and water

Worldwide, primarily human-to-human transmission

Clinical Features:
Intestinal: Intermittent diarrhea, abdominal pain, nausea, anorexia, malaise, fatigue, poor weight gain, unexplained eosinophilia.  The most common symptoms in patients infected with this parasite appear to be intermittent diarrhea and fatigue. In some patients, both the organism and the symptoms persist or reappear until appropriate treatment is initiated. Clinicians should include infection with D. fragilis in their differential diagnosis in patients presenting with abdominal pain, diarrhea, unexplained flatulence, nausea, and vomiting. 

Clinical Specimen:
Intestinal:  Stool

Laboratory Diagnosis:
Intestinal:  Ova and Parasite examination (concentration, permanent stained smear); permanent stained smear mandatory for identification.  It is particularly important that permanently stained smears of stool material be examined with an oil immersion objective (100´). These organisms have been recovered in formed stool; therefore a permanent stained smear must be prepared for every stool sample submitted for a parasite examination.

Organism Description:
Trophozoite:  Round, 1 (20-40%) nucleus or 2 nuclei (60-80%); nuclei tend to fragment into 3-5 granules.  Cytoplasm often filled with ingested debris; size range of trophozoites is tremendous, even on a single slide.

Laboratory Report:
Dientamoeba fragilis (indicate trophozoites)

Garcia, L.S. 2007.  Diagnostic Medical Parasitology, 5th ed., ASM Press, Washington, D.C.

Improved hygiene, adequate disposal of fecal waste, adequate washing of contaminated fruits and vegetables

This organism can mimic other protozoa such as Endolimax nanaIn many parts of the United States, this organism is found more often than Giardia.  Although often seen in pediatric patients, the infection is not limited to this population; all age groups can become infected.