Entamoeba histolytica is a topic covered in the Johns Hopkins ABX Guide.

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MICROBIOLOGY

  • 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.
    • Fecal anti-Gal/GalNAc lectin IgA protective against infection.[4]
    • Disease occurs in minority (10%) of infections.[1]
  • 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.[7]
    • Occurs primarily in developing countries, also seen in immigrants from and travelers to endemic areas and those with oral-anal or oral-fecal contact.

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Last updated: March 1, 2017