Life Cycle of Balantidium coli


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




The cyst is the infective stage of Balantium coli life cycle.  Once the cyst is ingested via feces-contaminated food or water, it passes through the host digestive system.  The tough cyst wall allows the cyst to resist degradation in the acidic environment of the stomach and the basic environment of the small intestine until it reaches the large intestine.  There, excystation takes place. Excystation produces a trophozoite from the cyst stage.




The motile trophozoite then resides in the lumen of the large intestine, feeding on intestinal bacterial flora and intestinal nutrients.  Trophozoites multiply by asexual binary fission or sexual conjugation (with the exchange of nuclear material).  The trophozoite may become invasive and penetrate the mucosa of the large intestine (See Clinical Presentation).  Trophozoites are released with the feces, and encyst to form new cysts.  Encystation takes place in the rectum of the host as feces are dehydrated or soon after the feces have been excreted.



Cysts in the environment are then ready to infect another host.

Excystation in large intestine







The Parasite


Life Cycle


Animal Reservoirs

Clinical Presentation





Public Health Interventions


Glossary of terms

References and links