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; 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.[5]
  • Fecal anti-Gal/GalNAc lectin IgA protective against infection.[10]
  • Disease occurs in a 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.[6]
  • Occurs primarily in developing countries, also seen in immigrants from and travelers to endemic areas and those with oral-anal or oral-fecal contact.[7]