Dientamoeba fragilis
- Parasite
- For completeness
A gut protozoan of the colon, related to trichomonads but without flagella. It may cause diarrhea and belly pain, mostly in children.
Quick facts
- Type
- Parasite · Intestinal and urogenital protozoa
- Gram / shape
- Amoeboid trophozoite
- Spread
- Fecal-oral · Rare cyst-like forms have been described
- Causes
- Dientamoebiasis
- Treatment
- Only symptomatic patients
At a glance
- Shape
- Amoeboid trophozoite, usually with two nuclei; no true cyst stage
- Family
- Dientamoebidae (Trichomonadida)
- Type
- Intestinal protozoan (trichomonad without flagella)
- Stain
- Permanent stains of fresh stool (trichrome, iron hematoxylin)
- Size
- Trophozoite about 5 to 15 µm
Morphology
- Trophozoite with one or, more often, two nuclei; each nucleus has a karyosome broken into 4 to 8 granules.
- Clear angular or broad pseudopods; no external flagella.
- Fragile: it degenerates quickly, so it is missed in concentrated or old samples.
Transmission
- Fecal-oral, probably carried inside the eggs of Enterobius vermicularis (pinworm).
- Rare cyst-like forms have been described, but their role is unclear.
- Common in families and children's institutions.
Reservoir: Humans
Isolation precautions
What the care team adds to standard precautions.
- Standard
Life cycle
- Trophozoites live in the cecum and colon mucosa.
- They multiply by binary fission.
- Trophozoites pass in stool; they do not survive long outside.
- Transmission is thought to happen inside pinworm eggs that protect them.
- A new host swallows the eggs, and the parasites are released in the colon.
Virulence factors
- Mucosal irritation and mild inflammation in the colon; it does not invade tissue.
- Its pathogenicity is still debated: many carriers have no symptoms.
Diseases it causes
- Dientamoebiasis: diarrhea, abdominal pain, flatulence and poor appetite; may become chronic. Acute (viral) gastroenteritis →
- It has been linked to irritable bowel-like symptoms and, rarely, to a picture that mimics appendicitis. Irritable bowel syndrome →
Clinical picture
- More common in children; often with pinworm coinfection.
- Mild eosinophilia may be present.
- Asymptomatic carriage is frequent.
Diagnosis
- Fresh stool fixed at once and stained with a permanent stain (trichrome): binucleate trophozoites.
- Usually missed in concentration methods; several samples improve yield.
- Can be confused with Endolimax nana or Entamoeba hartmanni.
- Stool PCR is used in some labs but results vary between platforms.
Treatment
Only symptomatic patients in whom it is the sole organism found are treated. Options include paromomycin, nitroimidazoles (metronidazole, secnidazole, tinidazole) and tetracyclines such as doxycycline; benzimidazoles do not work. Treating a coexisting pinworm infection makes sense.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Handwashing and nail hygiene in children.
- Treating pinworm in the household.
- Safe water and sanitation.
Test yourself
Think of the answer, then tap the question to see it.
Why is Dientamoeba fragilis not a true amoeba?
It is a trichomonad flagellate that has no external flagella; it only looks amoeboid.
Which helminth is thought to carry Dientamoeba between people?
Enterobius vermicularis; the protozoan probably travels inside pinworm eggs.
Which lab method is needed to see Dientamoeba?
A permanent stain (such as trichrome) of fresh, promptly fixed stool; concentration methods usually miss it.
What does the typical trophozoite look like?
Small, with two nuclei whose karyosomes are broken into several granules, and no flagella.
Connections
← Back to the group: Intestinal and urogenital protozoa
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: CDC - DPDx - Dientamoeba fragilis Infection (CDC, 2024); Clinical Care of Dientamobea fragilis | Dientamoeba fragilis | CDC (CDC, 2024); Stool Specimens – Intestinal Parasites: Comparative Morphology Tables (CDC, 2024).
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Representative model, for educational purposes only.