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 mcm (1). The thick-walled cyst present in the stools (1) is believed to be responsible for external transmission, possibly by the fecal-oral route through ingestion of contaminated water or food (2). The cysts infect epithelial cells of the digestive tract and multiply asexually (3,4). Vacuolar forms of the parasite give origin to multi-vacuolar (5a) and ameboid (5b) forms. The multi-vacuolar develops into a pre-cyst (6a) that gives origin to a thin-walled cyst (7a), thought to be responsible for autoinfection. The ameboid form gives origin to a pre-cyst (6b), which develops into thick-walled cyst by schizogony (7b). The thick-walled cyst is excreted in feces (1).
Originally published in: Singh M, Suresh K, Ho LC, et al. Elucidation of the life cycle of the intestinal protozoan Blastocystis hominis. Parasitol Res 1995; 81:449. Reproduced with kind permission from Springer Science + Business Media B.V. Reproduced from: Centers for Disease Control and Prevention. DPDx: Blastocystis hominis. Available at:
http://www.cdc.gov/dpdx/blastocystis/index.html.
