Parasite
Balantidium coli
Only ciliated protozoan that infects humans
bal-an-TID-ee-um KOH-lie
High-yield clue
A large, cilia-covered trophozoite with a kidney-bean-shaped macronucleus is the unmistakable study clue.
Overview
The only ciliated protozoan known to cause human disease, a large intestinal parasite associated with pigs as the reservoir. It matters as the classic ciliate contrast to amebic colon pathogens.
Classification
- Protozoa
- Ciliate
- Trophozoite + cyst stages
- Largest protozoan pathogen of humans
Lab & identification clues
- Cilia-covered motile trophozoite
- Kidney-bean macronucleus vocabulary
- Cytostome (mouth-pore) feature
- Stool ova-and-parasite exam concept
Associations
- Pigs as primary reservoir host
- Fecal-oral / contaminated-water transmission
- Colon-invasion / dysentery vocabulary
- Zoonotic epidemiology framing
Commonly confused with
- Entamoeba histolytica
- Cryptosporidium
Your notes
Original student-study summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment, dosing, or specimen-handling guidance.