Chilomastix mesnili is an apparently nonpathogenic (i.e., commensal) flagellate found worldwide in the human cecum and/or colon. Non-human animals may serve as a reservoir for Chilomastix. The resistant cyst stage in the life cycle of Chilomastix is responsible for transmission. Both cysts and trophozoites can be found in the feces (diagnostic stages). Infection occurs by the ingestion of cysts in contaminated water or food or by the fecal-oral route (via hands or fomites, i.e., inanimate objects such as towels that transmit infectious organisms to a host). In the large (and possibly small) intestine, excystation releases trophozoites.