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ESSENTIALS OF DIAGNOSIS
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ESSENTIALS OF DIAGNOSIS
Organisms or antigen present in stools or abscess aspirate.
Positive serologic tests with colitis or hepatic abscess, but these may represent prior infections.
Mild to moderate colitis with recurrent diarrhea.
Severe colitis: bloody diarrhea, fever, and abdominal pain, with potential progression to hemorrhage or perforation.
Hepatic abscess: fever, hepatomegaly, and abdominal pain.
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GENERAL CONSIDERATIONS
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The Entamoeba complex contains three morphologically identical species: Entamoeba dispar and Entamoeba moshkovskii, which are avirulent, and Entamoeba histolytica, which may be an avirulent intestinal commensal or lead to serious disease. Disease follows penetration of E histolytica into the intestinal wall, resulting in diarrhea, and with severe involvement, dysentery or extraintestinal disease, most commonly liver abscess.
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E histolytica infections are present worldwide but are most prevalent in subtropical and tropical areas under conditions of crowding, poor sanitation, and poor nutrition. Of the estimated 500 million persons worldwide infected with Entamoeba, most are infected with E dispar and an estimated 10% with E histolytica. The prevalence of E moshkovskii is unknown. Mortality from invasive E histolytica infections is estimated at 100,000 per year.
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Humans are the only established E histolytica host. Transmission occurs through ingestion of cysts from fecally contaminated food or water (eFigure 37–17), facilitated by person-to-person spread, flies and other arthropods as mechanical vectors, and use of human excrement as fertilizer. Urban outbreaks have occurred because of common-source water contamination.
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