Practical Parasitology

Blastocystis hominis

• Much debate still surrounds this organism and its role as a pathogen. (54)(55)(56)(57)(58)
• Classified as a protozoan.
• Most B. hominis appear as an organism 5 - 20 microns in diameter with two nuclei appearing most often at opposite poles of the cell.
• A central vacuole is present surrounded by a layer containing various organelles such as the nuclei and mitochondria.
• One study suggests that because of the great diversity in cell morphology B. hominis is often missed in the laboratory examination.(55)
• Laboratory diagnosis is based on finding the cells in significant quantities with no other parasite present (pathogen or non-pathogen).
• Metronidazole is drug of choice with dosage as follows. (54) 250 - 750 mg. three times per day for 5 - 10 days, 200 mg. four times per day for up to 7 days or 2g/day for 5 days.
• There has been some suggestion however that metronidazole is ineffective against B. hominis (25)

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David M. Raymondo
MLT, CLS(m)
Professional Affiliation: Gamma-Dynacare Medical Laboratories, Ottawa, Ontario, Canada
Gamma-Dynacare is a Division of the Dynacare Health Group