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[Blastocystis hominis]

Blastocystis hominis stages were reproduced from Singh M, Suresh K, Ho LC, Ng GC, Yap EH. Elucidation of the life cycle of the intestinal protozoan Blastocystis hominis. Parasitol Res 1995;81:449.  Copyright held by Springer-Verlag and reproduced here by permission of Springer-Verlag and M. Singh.

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 .