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- Protozoan species, genus Entamoeba.
- E. histolytica is morphologically similar to E. dispar, E. moshkovskii, and E. bangladeshi.
- Histolytic - histo + lyein (Greek) to loosen, trophozoites contain cytolytic and proteolytic enzymes, including collagenase and proteinases, and lyze neutrophils and macrophages.
- Cysts are ingested and excystation occurs in the distal ileum and cecum. Motile trophozoites are released and migrate to the large intestine. Trophozoite surface protein and key virulence factor, Gal/GalNAc lectin, mediates adherence to host cells.
- Cysts found in contaminated water or food. Cysts remain viable outside host in water, soil, and sewage for weeks or months.
- Infecting dose is fewer than 10 cysts.
- Occurs primarily in developing countries, also seen in immigrants from and travelers to endemic areas and those with oral-anal or oral-fecal contact.