Balantidium coli causes balantidiasis. Balantidium exists in two forms: a vegetative trophozoite  and  a  cyst.   They   are  characterized  by  having  two nuclei: a large macronucleus for growth and metabolism and a small micronucleus for cell division.

 

The cyst form is ingested in contaminated food and water and develops into trophozoites in the large intestine. The large intestines become ulcerated and periods of alternating diarrhea and constipation result.