Entamoeba histolytica can live in the large intestine (colon) without causing disease. However, sometimes, it invades the colon wall causing colitis, acute dysentery, or chronic diarrhea. The infection can also spread through the blood to the liver and rarely, to the lungs, brain or other organs. This condition can occur anywhere in the world, but it is most common in tropical areas with crowded living conditions and poor sanitation. Africa, Latin America, Southeast Asia, and India have significant health problems associated with this disease. Transmission occurs through ingestion of cysts in fecally contaminated food or water, which is common when human excrement is used as fertilizer. It can also be spread person-to-person -- particularly via oral or anal contact. Cockroaches and house flies can also spread the cysts. There are an estimated 50 million cases worldwide of amebiasis with 40,000 to 50,000 deaths annually.
Typical symptoms of intestinal amebiasis consist of frequent diarrheal bowel movements with cramps or colicky abdominal pain. Pain on defecation (tenesmus) is common. The diarrhea may contain blood or mucus. Uncomplicated attacks may last up to two weeks, and recurrences are common unless the diagnosis is made and the individual is treated. Spread of E. histolytica into the wall of the colon may occur in 8-10% of cases and to the liver in approximately 1%.
Malnutrition, old age, pregnancy, use of steroids, malignancy (cancer), and alcoholism predispose a person to more severe disease, as does immunosuppression. Recent travel to a tropical region is a risk factor. In the US, amebiasis is most common among people who engage in anal intercourse and residents of institutions.
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