The Parasite: Balantidium coli



Balantidium coli is the only ciliate known to parasitize humans. Ciliates represent a phylum of protozoa characterized, in at least one stage of development, by simple or compound ciliary organelles on the surface of their membranes that are used for locomotion. Ciliates have 2 nuclei (one macronucleus and one micronucleus) and reproduce by transverse binary fission, conjugation, autogamy, and cytogamy.


Balantidium coli has 2 contractile vacuoles. Although contractile vacuoles are common to ciliates, they are rare in parasitic protozoa, which suggests that Balantidium coli has a unique osmoregulatory capacity.


Balantidium coli has 2 developmental stages: a trophozoite stage and a cyst stage. (See Morphology and Life Cycle for descriptions of the stages.)




Kingdom Protista

Phylum Ciliophora

Class Litostomatea

Order Vestibuliferida

Balantidium coli










Balantidium coli has been known for more than a century, and yet the pathogenicity of the protozoa and how humans acquire it are still not fully understood.




The Parasite


Life Cycle


Animal Reservoirs

Clinical Presentation





Public Health Interventions


Glossary of terms

References and links