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.
Microorganisms in this group
- Entamoeba histolyticaAn amoeba caught from water or food contaminated with feces. It can cause bloody dysentery and liver abscesses.Exam priority: high
- Giardia duodenalisA small-intestine parasite caught from contaminated water or food. It causes greasy diarrhea, gas and malabsorption, especially in children.Exam priority: high
- Trichomonas vaginalisA sexually transmitted parasite that causes frothy, foul-smelling vaginal discharge; in men it is usually silent.Exam priority: medium
- 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
- Balantioides coliThe only ciliate that infects humans. It comes from water or food contaminated with pig feces and can cause dysentery.For completeness
- 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
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.
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 (CDC, 2024); CDC - DPDx - Giardiasis (CDC, 2024); CDC - DPDx - Intestinal (Non-Pathogenic) Amebae (CDC, 2024).
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Representative model, for educational purposes only.