Entamoeba histolytica, the cause of amebiasis, infects ~10% of the world's population and is the third most common cause of death from parasitic disease (after schistosomiasis and malaria). Infection follows ingestion of cysts from fecally contaminated water, food, or hands. Motile trophozoites are released from cysts in the small intestine and then cause infection in the large bowel. Trophozoites may be shed in stool (in active dysentery) or encyst. Excreted cysts survive for weeks in a moist environment.