Dientamoeba fragilis

Introduction

An ameboid pathogen that infects the colon.

Epidemiology

• occurs especially in young children
• human to human fecal-oral spread
• may spread by ingestion of D. fragilis-infected Enterobius vermicularis (pinworm) eggs

Pathology

• no cyst stage has been described
• generally not associated with other intestinal protozoa
• trophozoites infect mucosal crypt cells of intestines
  • eosinophilic inflammatory response
• infection with D. fragilis is associated with a 10-20 fold increased incidence of enterobiasis

Clinical manifestations

• 25% of infected individuals have symptoms
• nonbloody diarrhea & abdominal distension
• nausea/vomiting
• anorexia, weight loss, flatulence
• headache, fever, malaise,fatigue

Laboratory

• diagnosis is made by recovery of trophozoites in feces
  • trichrome stain
• multiple specimens may need to be examined because of intermittent shedding
• trophozoites
  • found in greatest numbers in the last portion of the stool
  • measure 5-15 um in size, generally 9-12 um
  • motile on wet mounts with angular pseudopods
  • 65-90% of contain 2 nuclei
  • trophozoites with a single nucleus may be confused with trophozoites Endolimax nana or Iodamoeba butschii
  • cytoplasm is finely granular & often contains ingested bacteria
  • delicate & may be easily overlooked on stained slides
• immunofluorescence method described, but not yet commercially available
• Dientamoeba fragilis DNA in stool

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Management

• iodoquinol 650 mg PO TID for 20 days
• paromomycin 25-30 mg/kg/day divided TID for 7 days
• tetracycline 500 mg QID for 10 days

More general terms

• Dientamoeba

Additional terms

• Enterobius vermicularis (pinworm)