Proposed life cycle of Blastocystis hominis


Knowledge of the life cycle and transmission is still under investigation, therefore this is a proposed life cycle for B. hominis.  The classic form found in human stools is the cyst, which varies tremendously in size from 6 to 40 μm  .  The thick-walled cyst present in the stools  is believed to be responsible for external transmission, possibly by the fecal-oral route through ingestion of contaminated water or food  .  The cysts infect epithelial cells of the digestive tract and multiply asexually ( ,  ).  Vacuolar forms of the parasite give origin to multi vacuolar  and ameboid  forms.  The multi-vacuolar develops into a pre-cyst  that gives origin to a thin-walled cyst  , thought to be responsible for autoinfection.  The ameboid form gives origin to a pre-cyst  , which develops into thick-walled cyst by schizogony  .  The thick-walled cyst is excreted in feces  .