noun, plural: balantidiases
Baantidiasis is an infection caused by the parasitic ciliate Balantidium coli. This ciliate has two forms in its life cycle: trophozoite and cyst. The trophozoite B. coli is regarded as the largest protozoan to infect humans. Its size is about 30 to 150 µm in length and 25 to 120 µm in width.1 It has a perceptible sausage-like macronucleus and a spherical, less prominent micronucleus when viewed under a microscope. The trophozoite has a ciliated surface. It replicates by transverse binary fission. As a parasite, the trophozoite colonizes the large intestine where it feeds on the intestinal flora. It may form into a cyst, which is released to the environment together with the feces. The cyst has a tough cyst wall by being comprised of one or more layers. It is non-motile. However, the mature cyst of B. coli is its infective stage. When a host ingests food or water contaminated with this cyst, the cyst then develops into a trophozoite when it reaches the small intestine.
The hosts are typically pigs, rats, and other mammals. Balantidiasis is a zoonotic disease; humans may become a host and may be harmed by the presence of this protozoan. One of the symptoms of balantidiasis in humans is either diarrhea or constipation. In pigs, balantidiasis does not cause harm, and, as such, is usually asymptomatic.
1 Roberts, L. S., Janovy Jr., J. Schmidt, G. D., & Roberts, L. S. (2009). Foundations of Parasitology (8th ed.). New York: McGraw-Hill.