[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/) › Balantioides coli

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

# Balantioides coli

- Parasite
- For completeness

The only ciliate that infects humans. It comes from water or food contaminated with pig feces and can cause dysentery.

Updated 2026-11-01

Also called: Balantidium coli (old name)

## Key points

- The only pathogenic ciliate of humans; the largest protozoan in stool.
- Reservoir: the pig.
- Dysentery resembling amoebiasis.
- Tetracyclines as the classic treatment.

## At a glance

**Shape**
Oval trophozoite covered in cilia, with a kidney-shaped macronucleus

**Family**
Balantidiidae

**Type**
Intestinal ciliated protozoan (trophozoite and cyst)

**Stain**
Direct stool exam (visible without stain because of its size)

**Size**
Trophozoite about 40 to 200 µm; cyst about 50 to 70 µm

## Morphology

- Large trophozoite covered in cilia, with a cell mouth (cytostome).
- Kidney-shaped macronucleus and a small micronucleus.
- Round, thick-walled cyst.
- The largest protozoan seen in human stool.

## Transmission

- Fecal-oral: water or food contaminated with cysts, mainly from pig feces.
- More common where pigs are raised and sanitation is poor.

**Reservoir:** Pigs (main); Humans, rodents and primates

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- Cysts are swallowed with contaminated water or food.
- Trophozoites are released in the small intestine and move to the colon.
- They multiply by binary fission and may exchange genetic material (conjugation).
- Some invade the colonic wall and cause ulcers.
- Trophozoites encyst and the cysts leave in the feces.

## Virulence factors

- Hyaluronidase and ciliary motility that help it invade the mucosa.
- Colonic ulcers similar to those of amoebiasis.

## Diseases it causes

- Balantidiasis: from silent infection to colitis with diarrhea or dysentery; rarely perforation or extraintestinal disease.

## Clinical picture

- Most people have no symptoms.
- Intermittent chronic diarrhea or dysentery with abdominal pain.
- Severe forms in malnourished or immunocompromised people.

## Diagnosis

- Fresh stool exam: large trophozoites with fast ciliary motion; examined promptly because they die outside the colon.
- Serial samples, since shedding is intermittent.
- Colonic biopsy at colonoscopy.

## Treatment

Tetracyclines are the classic option; metronidazole or iodoquinol are alternatives.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Tetracycline](https://durgical.com/en/pharmacology/tetracycline/)
- [Metronidazole](https://durgical.com/en/pharmacology/metronidazole/)

## Prevention

- Keeping pig farming away from water sources and homes.
- Safe water, handwashing and excreta management.

**Vaccine:** There is no vaccine.

## In Colombia

It is uncommon in Colombia and is linked to rural areas where pigs are kept near the home.

## Memory aid

«The hairy pig parasite»: a cilia-covered giant from the pigsty that can cause dysentery.

## Test yourself

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

## What is unique about Balantioides coli among human parasites?

It is the only ciliated protozoan that infects humans and the largest one seen in stool.

## What is its main reservoir?

The pig; infection is more common where pigs are raised and sanitation is lacking.

## What illness does it cause when it invades the colon?

Colitis with diarrhea or dysentery and ulcers, resembling intestinal amoebiasis.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/balantioides-coli/)

## Related

- [Entamoeba histolytica](https://durgical.com/en/microbiology/entamoeba-histolytica/)

## 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.

[← 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: [Balantidiasis](https://www.cdc.gov/dpdx/balantidiasis/index.html) (CDC (DPDx), 2024); Parasitosis humanas (6.ª ed.), Botero D, Restrepo M (Corporación para Investigaciones Biológicas (CIB), 2019).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

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/balantioides-coli/