MICROBIOLOGY

• E. histolytica, an extracellular parasitic protozoan, is distributed worldwide. Life cycle includes cysts and trophozoites.[15]
  • The mature, quadrinucleate cysts are resistant to desiccation and persist in moist environments for weeks, whereas trophozoites do not survive outside the host.
  • Cysts are passed in feces and, if ingested, transmit the infection. Excystation occurs in terminal ileum. Each cyst produces 8 motile trophozoites, which migrate to large intestine and invade colonic mucosa.
  • Galactose/N-acetyl-D-galactosamine (Gal/GalNAc)-specific lectin mediates parasite adhesion to colonic mucin.[5]
  • Tissue invasion is related to penetration of mucous layer and killing of epithelial cells by amoebapore lytic peptides.
  • Deep ulcerations spread in the submucosa, form flask-shaped ulcers, and cause microhemorrhages.
• Immunity is mediated by mucosal IgA recognition of Gal/GalNAc lectin. Immunocompromised hosts are more susceptible to symptomatic amebiasis.
• Morphologically-identical Entamoeba spp. include: E. dispar, E moshkovskii, and E. bangladeshi, and are not routinely associated with disease.
  • E. dispar may have pathogenic strains that are associated with intestinal and liver lesions and, like E. histolytica, may be seen with ingested erythrocytes.[5]