Taxonomy: f. Entamoebidae
Animal: Entamoeba histolytica 5 09.jpg
Entamoeba histolytica trophozoite containing ingested red cells which is diagnostic. Trophozoite is 12 - 60 microns (invasive forms greater than 20). Single nucleus with fine peripheral chromatin and small compact karyosome in faecal smear stained with Trichrome. 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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