Paul G. Auwaerter, M.D.
Blastocystis is a topic covered in the Johns Hopkins ABX Guide.

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  • Parasite 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, 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 historically used to denote infection but likely 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).
  • Life cycle not clearly known, likely transmission through fecal-oral routes, with contaminated water a high suspect. Cysts may infect epithelial cells of GI tract.

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Last updated: May 4, 2019