Amebiasis is a parasitic infection of the intestines caused by entamoeba histolytica. It is common in tropical areas of the world where sanitation is poor, allowing food and water supplies to be exposed to fecal contamination. Epidemiology. E. histolytica is an endemic and travel-associated, tissue-invasive protozoan transmitted via the fecal-oral route. It is common in institutionalized patients and homosexual males. In the United States, the prevalence is about 5%. Pathology. The infection starts with ingestion of the cysts. The excystation occurs in the colon with the release of trophozoites, which invade the mucosa and lead to mucosal inflammation and ulceration similar to that seen in idiopathic inflammatory bowel disease. The classic lesions of amebiasis are the â€˜flask-shaped ulcersâ€™ that may extend to the submucosa. Clinical disease. The infection manifests in a spectrum of disease with varying severity. In the mild form, patients have crampy abdominal pain, intermittent diarrhea, and tenesmus. In the more severe form, there is bloody diarrhea with abdominal pain, tenesmus, and fever. Acute abdomen secondary to perforation or peritonitis may be seen. The infection may encompass the entire colon but may be in the form of amebomas, which are single or multiple annular inflammatory lesions more often seen in the cecum or the ascending colon. Diagnosis is made by the demonstration of the organism in the stool. In mildly affected patients and in carriers, cysts are usually present in the stool. Trophozoites may be demonstrated in stool or biopsy specimens obtained from ulcer margins at sigmoidoscopy or colonoscopy. In amebic colitis, the serology by indirect hemagglutination test is positive in greater than 90% of patients.