[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Intestinal and urogenital protozoa](https://durgical.com/en/microbiology/groups/intestinal-and-urogenital-protozoa/) › Dientamoeba fragilis

# 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.

Updated Nov 13, 2026

## Quick facts

**Type**
Parasite · [Intestinal and urogenital protozoa](https://durgical.com/en/microbiology/groups/intestinal-and-urogenital-protozoa/)

**Gram / shape**
Amoeboid trophozoite

**Spread**
Fecal-oral · Rare cyst-like forms have been described

**Causes**
Dientamoebiasis

**Treatment**
Only symptomatic patients

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- Life cycle
- Memory aid
- What the colours mean

- Clinical Virulence factors
- Diseases it causes
- Clinical picture
- Diagnosis

- Treatment Treatment
- Prevention

- Study Test yourself

- Connections Connections

## Key points

- Despite its name, it is not an amoeba: it is a trichomonad that lost its flagella.
- Binucleate trophozoite with fragmented karyosomes; no cyst.
- Needs a permanent stain of fresh stool; concentration misses it.
- Linked to Enterobius, whose eggs probably carry it.

## 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 →](https://durgical.com/en/conditions/acute-gastroenteritis/)
- It has been linked to irritable bowel-like symptoms and, rarely, to a picture that mimics appendicitis. [Irritable bowel syndrome →](https://durgical.com/en/conditions/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:

- [Paromomycin](https://durgical.com/en/pharmacology/paromomycin/)
- [Metronidazole](https://durgical.com/en/pharmacology/metronidazole/)
- [Secnidazole](https://durgical.com/en/pharmacology/secnidazole/)
- [Tinidazole](https://durgical.com/en/pharmacology/tinidazole/)
- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)

## Prevention

- Handwashing and nail hygiene in children.
- Treating pinworm in the household.
- Safe water and sanitation.

## Memory aid

«Two eyes, no tail, pinworm taxi»: two nuclei like eyes, no flagellum, and it travels inside pinworm eggs.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/dientamoeba-fragilis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

## Connections

## Related 6

- [Enterobius vermicularis](https://durgical.com/en/microbiology/enterobius-vermicularis/)
- [Giardia duodenalis](https://durgical.com/en/microbiology/giardia-duodenalis/)
- [Trichomonas vaginalis](https://durgical.com/en/microbiology/trichomonas-vaginalis/)
- [Commensal intestinal amoebae (Entamoeba coli, E. dispar, Endolimax nana and others)](https://durgical.com/en/microbiology/commensal-intestinal-amoebae/)
- [Commensal flagellates (Chilomastix, Pentatrichomonas, Enteromonas, Retortamonas, Trichomonas tenax)](https://durgical.com/en/microbiology/commensal-flagellates/)
- [Blastocystis spp.](https://durgical.com/en/microbiology/blastocystis-spp/)

## Related conditions 2

- [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/)
- [Irritable bowel syndrome](https://durgical.com/en/conditions/irritable-bowel-syndrome/)

[← Back to the group: Intestinal and urogenital protozoa](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/dpdx/dientamoeba/index.html) (CDC, 2024); [Clinical Care of Dientamobea fragilis | Dientamoeba fragilis | CDC](https://www.cdc.gov/dientamoeba/hcp/clinical-care/index.html) (CDC, 2024); [Stool Specimens – Intestinal Parasites: Comparative Morphology Tables](https://www.cdc.gov/dpdx/diagnosticProcedures/stool/morphcomp.html) (CDC, 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/dientamoeba-fragilis/