Taxonomy: f. Entamoebidae
Animal: Entamoeba histolytica 1 05.jpg
Sites: Gut
Entamoeba histolytica cyst - spherical 10 - 20 microns (average 12 - 15). Mature cyst has 4 nuclei - fine peripheral chromatin, small compact central karyosome and elongate chromatoidal bodies which have blunt or rounded smooth edges in faecal preparation stained with Iodine. Microscopy cannot differentiate between the virulent E. histolytica and the non-virulent E. dispar which never invades or causes a serological response. E.histolytica always elicits a serological response whether it is invasive or whether the person is asymptomatic -- only 10 precent do develop serious disease. The presence of red cells in trophozoites is a predictor of serious disease. Analyses of four types of isoenzymes, molecular methods and ELISA tests of lectins distinguishes Entamoeba histolytica from E. dispar. E. histolytica isolates differ in sequences of many homologous genes and in their pathogenic potential; the molecular basis to account for variability in pathogenicity is not understood.

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