Entamoeba

Cysts of Entamoeba contaminate water and are ingested with drinking water or contaminated food. Within the host, which are usually mammals but may be other vertebrates or even invertebrates, small trophozoites are released from the cyst. These usually feed on particulate material within the host's gut, grow, and divide by fission. Trophozoites passing in the feces of the host begin to encyst as the fecal material dehydrates. Within the cyst the parasite divides to form several trophozoites; the number varies according to species. The cyst wall provides some protection against chemical conditions in the external environment and may remain infective for up to 2 weeks.

Pathogenic species such as E. histolytica can hydrolyze host tissues and secondarily invade deeper tissues. Bacteria from the intestine can enter these lesions and cause serious infections.