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Also called amoebic dysentery, amebiasis can take the form of either an acute or a chronic protozoal infection. Extra intestinal amebiasis can induce hepatic abscess and infection of the lungs, pleural cavity, pericardium, peritoneum and, rarely, the brain.

Amebiasis occurs worldwide; about 90% of infections are asymptomatic and the rest produce symptoms ranging from amoebic dysentery to abscesses of the liver and other organs. It's the third most common cause of death from paralytic disease, after schistosomiasis and malaria. It's most common in the tropics, subtropics, and other areas which poor sanitation and health practices.


Amebiasis is caused by Entamoeba histolytica. This protozoan has two stages: during the cystic stage, it can survive outside the body; during the trophozoite stage, it can't.

Transmission occurs through ingesting stool­contaminated food or water or through oral-anal sexual practices. The ingested cysts pass through the intestine, where digestive secretions break them down, freeing the motile trophozoites within. The trophozoites then multiply and either invade and ulcerate the mucosa of the large intestine or simply feed on intestinal bacteria. As the trophozoites are carried slowly toward the rectum, they are encysted and then excreted in stool. Humans are the principal carriers.

Signs and symptoms

People exposed to this parasite may experience mild or severe symptoms or no symptoms at all. Fortunately, most exposed people do not become seriously ill. The mild form of amebiasis includes nausea, loose stools, weight loss, abdominal tenderness and occasional fever. Rarely, the parasite will invade the body beyond the intestines and cause a more serious infection, such as a liver abscess.

Diagnostic tests 

Examination of stools under a microscope is the most common way for a doctor to diagnose amebiasis. Sometimes, several stool samples must be obtained because the number of amoeba being passed in the stool, which varies from day to day, may be too low to detect from any single sample.


The patient with amebiasis is treated with metronidazole, the preferred amebicide for intestinal and extraintestinal infection that causes symptoms of acute colitis or liver abscess. Other agents for asymptomatic carriers include diloxamine furoate, iodoquinol, or paromomysin. For liver abscess without intestinal infections, the patient receives metronidazole, tinidazole, imidazole, plus the other agents as listed above for the asymptomatic carrier.

Exploratory surgery is hazardous because it can lead to peritonitis, perforation, and pericecal abscess. Percutaneous drainage of abscesses of the liver may be necessary, but surgery is usually reserved for patients with a perforation or rupture.


When traveling in tropical countries where poor sanitation exists, drink purified or boiled water and do not eat uncooked vegetables or unpeeled fruit. Public health measures include water purification, water chlorination, and sewage treatment programs.

Safer sex measures, such as the use of condoms and dental dams for oral or anal contact, may help prevent infection.

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