BLASTOCYSTIS-HOMINIS - PAST AND FUTURE

Blastocystis hominis, classified as a yeast in 1912, was reclassified in 1967 as a protozoan and assigned to the family Sarcodina (amebae) in 1988. Protean morphology characterizes this human intestinal parasite and has delayed its recognition as a pathogen. An anaerobe, B. hominis has no cyst form. Typically, in clinical specimens, the entire center of the spherical cells is taken up with a membrane-bounded sphere, the central body, involved with asexual reproduction. In some infections, an ameba form may predominate or a third form, the granule cell, named for the highly visible mitochondria occupying the cytoplasm. The function of these mitochondria in the anaerobic B. hominis cell is not yet known but may be related to lipid synthesis. Diagnosis is made by microscopic examination of fresh or preserved concentrated fecal specimens, as either wet mounts or permanently stained smears. Reports of B. hominis in patients with gastrointestinal disease continue to increase, most of which support the concept that this protozoan is pathogenic. symptomatic infection often resolves within 3 days and is not treated. Chronic symptomatic cases are frequent, however, and may be incapacitating and require therapy. In recent years treatment has been almost exclusively with metronidazole.