Amebiasis, which is caused by a protozoan parasite, occurs worldwide, especially in regions with poor sanitation. High-risk areas (where up to 50% of the population carry the parasite) are Mexico, South America, India, and West and Southern Africa.

This potentially serious illness is caused by parasites that invade the wall of the large intestine, causing either acute dysentery or chronic diarrhea of variable severity. The parasites can also infect the liver, causing inflammation and liver abscess. In the carrier state, which is common, parasites live in the intestine without causing symptoms.

Transmission occurs through ingestion of fecally contaminated food or water. Flies can serve as carriers of the amebic cysts. Infected food handlers can spread the disease. Person-to-person contact is important in transmission; household members and sexual partners can easily become infected.

Signs and Symptoms

Symptoms of amebiasis are variable. You may be carrying the parasites and have no symptoms whatsoever. Mild illness causes crampy abdominal pain, little or no fever, and semiformed, foul-smelling stools. Mucus may be present but usually without blood. Soft stools or diarrhea may alternate with constipation. You may experience fatigue, loss of appetite, and some weight loss. The symptoms at this stage are similar to those of giardiasis.

More severe illness (amebic dysentery) is characterized by fever, bloody diarrhea, generalized abdominal tenderness, vomiting, and much greater toxicity. Illness at this stage represents a medical emergency and requires urgent care.

Travelers who develop amebic liver abscess usually don't have diarrhea or other intestinal symptoms. Instead, they may note fever, upper abdominal pain, and an enlarged, tender liver. Sweating, chills, weight loss, and fatigue may also be present.


Medical diagnosis of amebiasis is extremely important. Amebic dysentery must be distinguished from other infections causing bloody diarrhea (e.g., those due to Shigella, Campylobacter, Clostridium difflcile, and Yersinia). Reglonal enteritis and ulcerative colitis must be considered in the younger patient. In older persons, surgical conditions such as diverficulitis can mimic amebiasis.


Amebiasis is treated with Flagyl (metronidazole). Treatment eliminates cysts from the stool, thus preventing transmission of the disease to close contacts such as family members.