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[Microbiology](https://durgical.com/en/microbiology/) · [Parasites](https://durgical.com/en/microbiology/#d-parasite)

# Intestinal and urogenital protozoa

- Parasites

Amoebae, flagellates and ciliates of the gut and genital tract: Entamoeba, Giardia, Blastocystis, Balantioides, commensal amoebae and Trichomonas.

Updated 2026-11-01

## What they are

This group gathers the protozoa that live in the lumen of the gut or the urogenital tract. The intestinal ones spread fecal-orally through hardy cysts; Trichomonas spreads by sexual contact and forms no cysts. They are the core of stool microscopy and of parasitology questions in Colombian exams.

## What they share

- Two stages: trophozoite (active, multiplies) and cyst (hardy, infective), except Trichomonas, which has only a trophozoite.
- Fecal-oral spread through contaminated water, food or hands.
- Classic diagnosis: direct and concentrated stool exams on several samples; antigen tests and PCR where available.
- Finding commensal amoebae means fecal exposure, not disease.

## Key points

- E. histolytica: trophozoite with ingested red cells; dysentery and liver abscess.
- Giardia: greasy diarrhea and malabsorption; trophozoite with a ventral disk, four-nucleus cyst.
- Under the microscope E. histolytica looks the same as E. dispar: antigen tests or PCR are needed.
- Trichomonas vaginalis: trophozoite with flagella and undulating membrane; no cyst; sexually transmitted.

## Microorganisms in this group

- [**Entamoeba histolytica** An amoeba caught from water or food contaminated with feces. It can cause bloody dysentery and liver abscesses. Exam priority: high](https://durgical.com/en/microbiology/entamoeba-histolytica/)
- [**Giardia duodenalis** A small-intestine parasite caught from contaminated water or food. It causes greasy diarrhea, gas and malabsorption, especially in children. Exam priority: high](https://durgical.com/en/microbiology/giardia-duodenalis/)
- [**Trichomonas vaginalis** A sexually transmitted parasite that causes frothy, foul-smelling vaginal discharge; in men it is usually silent. Exam priority: medium](https://durgical.com/en/microbiology/trichomonas-vaginalis/)
- [**Blastocystis spp.** A very common organism in stool, including in healthy people. Whether it causes disease is unclear; it is usually an incidental finding. Exam priority: medium](https://durgical.com/en/microbiology/blastocystis-spp/)
- [**Balantioides coli** The only ciliate that infects humans. It comes from water or food contaminated with pig feces and can cause dysentery. For completeness](https://durgical.com/en/microbiology/balantioides-coli/)
- [**Commensal intestinal amoebae (Entamoeba coli, E. dispar, Endolimax nana and others)** Amoebae that live in the gut without causing disease. They often appear on stool reports and signal contact with feces, not a need to treat. For completeness](https://durgical.com/en/microbiology/commensal-intestinal-amoebae/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which stage of intestinal protozoa is infective?

The cyst, which survives the environment and stomach acid; trophozoites die quickly outside the body.

## Which protozoan in this group has no cyst stage?

Trichomonas vaginalis: it exists only as a trophozoite and spreads by sexual contact.

## What does Entamoeba coli in a stool report mean?

That there was exposure to fecal contamination; it is a commensal that causes no disease and is not a reason to treat on its own.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [CDC - DPDx - Amebiasis](https://www.cdc.gov/dpdx/amebiasis/index.html) (CDC, 2024); [CDC - DPDx - Giardiasis](https://www.cdc.gov/dpdx/giardiasis/index.html) (CDC, 2024); [CDC - DPDx - Intestinal (Non-Pathogenic) Amebae](https://www.cdc.gov/dpdx/intestinalamebae/index.html) (CDC, 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/groups/intestinal-and-urogenital-protozoa/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/groups/intestinal-and-urogenital-protozoa/