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Category: Gastroenterology | Infections

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Amoebiasis overview

Published: July 16, 2009. Updated: August 09, 2009

Amebiasis is an infection with the intestinal protozoan Entamoeba histolytica. About 90% of infections are asymptomatic, and the remaining 10% produce a spectrum of clinical syndromes ranging from dysentery to abscesses of the liver or other organs.

E. histolytica is acquired by ingestion of viable cysts from fecally contaminated water, food, or hands. Motile trophozoites are released from cysts in the small intestine and, in most patients, remain as harmless commensals in the large bowel. After encystation, infectious cysts are shed in the stool and can survive for several weeks in a moist environment. In some patients, the trophozoites invade either the bowel mucosa, causing symptomatic colitis, or the bloodstream, causing distant abscesses of the liver, lungs, or brain.

What are the symptoms?

Symptomatic amebic colitis develops 2 to 6 weeks after the ingestion of infectious cysts. Lower abdominal pain and mild diarrhea develop gradually and are followed by malaise, weight loss, and diffuse lower abdominal or back pain. Cecal involvement may mimic acute appendicitis. Patients with full-blown dysentery may pass 10 to 12 stools per day. The stools contain little fecal material and consist mainly of blood and mucus. In contrast to those with bacterial diarrhea, fewer than 40% of patients with amebic dysentery are febrile. Virtually all patients have heme-positive stools.

Most patients with liver abscess are febrile and have right-upper-quadrant pain, which may be dull or pleuritic in nature and radiate to the shoulder. Point tenderness over the liver and right-sided pleural effusion are common. Jaundice is rare. Although the initial site of infection is the colon, fewer than one-third of patients with an amebic abscess have active diarrhea.

Pleuropulmonary involvement, which is reported in 20 to 30% of patients, is the most frequent complication of amebic liver abscess. Manifestations include sterile effusions, contiguous spread from the liver, and rupture into the pleural space.


Patients have cysts in faeces, serodiagnosis are the mainstay of daignosis. Radiographic diagnosis confirms the presence of liver abscess.


luminal agents are used for eradication of cysts in patients with colitis or a liver abscess and treatment of asymptomatic carriers. Only two luminal drugs are available in the United States: iodoquinol and paromomycin.

The development of nitroimidazole compounds, especially metronidazole, was a major advance in the treatment of invasive amebiasis. Patients with amebic colitis should be treated with intravenous or oral metronidazole (750 mg three times daily for 5 to 10 days).

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