ABSTRACT
Balantidium coli is the only ciliated protozoan known to infect humans and is also the largest protozoan infecting humans and nonhuman primates. As a zoonotic organism, pigs form its asymptomatic natural reservoir, and other animals may also be involved. 1,2 Transmission of B. coli occurs primarily through ingestion of cysts via direct contact between hosts or indirect transmission through ingestion of contaminated food or water. 2 The main habitat for Balantidium is the cecum and colon. Human infection with Balantidium coli (i.e., balantidiosis, balantidial dysentery, or ciliary dysentery) may remain asymptomatic, or those infected may develop dysentery similar to that caused by Entamoeba histolytica. 3
