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.

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

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.

Diagnostic findings

  • Microscopy
  • Morphologic comparison with other intestinal parasites

Treatment:
Safe and effective drugs are available.  The drug of choice is iodoquinol.  Paromomycin*, tetracycline*, (contraindicated in children under age 8, pregnant and lactating women) or metronidazole can also be used.  

 * This drug is approved by the FDA, but considered investigational for this purpose.