Ingested quadrinucleate cysts of E. histolytica survive passage through the stomach. The organisms are released from their cysts in the small intestine, whereupon the cytoplasm and nuclei divide, yielding eight trophozoites. Upon reaching the lower intestine, these trophozoites begin feeding on mucus and intestinal bacteria. Many, but not all, strains produce a cytotoxic enzyme that kills intestinal epithelium on contact, allowing the organisms to penetrate the lining cells and enter deeper tissues of the intestinal wall. Sometimes, they penetrate into blood vessels and are carried to the liver or other body organs. Multiplication of the organisms and tissue destruction in the intestine and in other body tissues can result in amebic abscesses. The irritating effect of the amebas on the cells lining the intestine causes intestinal cramps and diarrhea. Due to intestinal ulceration, the diarrheal fluid is often bloody, and the condition is referred to as amebic dysentery.
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