Amebic colitis

Amebic colitis is caused by the protozoan Entamoeba histolytica parasitizing the human colon. In recent years, some reports have indicated that certain strains of Entamoeba histolytica are non-pathogenic and can survive long-term in the intestines of some individuals without causing symptoms. Non-pathogenic strains have surface antigen components different from those of pathogenic strains, do not produce proteolytic enzymes, and their hosts do not produce corresponding antibodies in the blood. Entamoeba histolytica exhibits two different morphological forms in its life cycle: the trophozoite and the cyst stage. After cysts are ingested by humans, mature cysts with four nuclei can excyst to become small trophozoites that parasitize the intestinal lumen, feeding on bacteria without damaging intestinal wall tissue, and reproduce by binary fission, growing well in the hypoxic ileocecal region. Only mature cysts with four nuclei are infectious; immature cysts with one or two nuclei are non-infectious but can develop into four-nucleated cysts under suitable external environmental conditions. Clinically, different manifestations may appear depending on the number of cysts ingested, the pathogenicity, and the host's resistance. Amebic colitis should be differentiated from acute and chronic enteritis, acute and chronic bacillary dysentery, nonspecific ulcerative colitis, and colon cancer. The most important examinations are stool examination and sigmoidoscopy. With improvements in nutrition and sanitary conditions, the infection rate in China has significantly decreased.