Tecausative agent of intestinal amebiasisis the single-celled protozoan parasite Entamoeba histolytica. Tis parasite is endemic in most tropical and subtropical areas of the world, where it causes millions of cases of dysentery and liver abscess each year. Infected persons display a wide range of disease severity, refecting the contributions of the patient’s immune and nutritional status, the infective dose and the pathogenic potential of the infecting organism. It is only one of several Entamoeba organisms that can reside in the human GI tract, which in the past has made diagnosis difcult. It is uniquely adapted to the conditions found in the lumen of the large intestine and as a result is sensitive to drugs that target anaerobic organisms.