Paul G. Auwaerter, M.D.


  • Parasites that are commonly found in the intestinal flora of humans.
    • Molecular studies have documented numerous genotypes, including usually zoonotic organisms, so B. hominis infection in humans is likely more heterogeneous than suspected.
  • Global presence is found also in animals, e.g., swine.
  • Appears as a thick-walled cyst (6-40 μm) in human feces [Fig].
  • Taxonomic classification is unclear. Based on RNA molecular analysis, B. hominis has been labeled as a stramenopile, similar to a large grouping of one and multi-celled protists such as algae, diatoms and slime molds. Confusion genomically also furthered as the organism has both a nuclear genome and organelle genome.
    • B. hominis was historically used to denote infection, but likely a more diverse group of Blastocystis causes human infection.
    • Suggest due to diversity, probably refer to Blastocystis spp. or Blastocystis spp. subtype n (n= subtype number, Stensvold classification).
  • The lifecycle is not well understood; likely transmission through fecal-oral routes, with contaminated water a high suspect. Cysts may infect epithelial cells of the GI tract.

There's more to see -- the rest of this topic is available only to subscribers.

Last updated: December 11, 2022