The methods of infection by Endamoeba histolytica are more easily followed if one bears in mind the life cycle of the parasite. In this, two phases are recognized: that of the trophozoites or free living forms, capable of life only within the human host, and that of the cysts which survive both within and outside the human host. The trophozoites are found in the wall of the large intestine, where in different conditions they cause varying degrees of ulceration. If during this process they invade the tributaries of the portal vein they are carried to the liver, where they may cause hepatitis or abscess. Less commonly, abscess of the lung, of the brain or of other organs may occur. If the trophozoites are passed by rectum in a dysenteric stool they die rapidly in water or on exposure to air, and if conceivably they could be ingested by another person
O'CONNOR FW. DISSEMINATION OF AMEBIASIS. Arch Intern Med (Chic). 1935;55(6):997–1000. doi:https://doi.org/10.1001/archinte.1935.00160240126007
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