BLASTOCYSTS HOMINIS REVISITED

Blastocystis hominis is a unicellular organism found commonly in the i ntestinal tract of humans and many other animals. Very little is known of the basic biology of the organism, and controversy surrounds its t axonomy and pathogenicity. Three morphological forms (vacuolar, granul ar, and ameboid) have been recognized, but recent studies have reveale d several additional forms (cyst, avacuolar, and multivacuolar). The b iochemistry of the organism has not been studied to any extent, and or ganelles and structures of unknown function and composition are presen t in the cells. Several life cycles have been proposed but not experim entally validated. The form used for transmission has not been defined . Infections with the organism are worldwide and appear in both immuno competent and immunodeficient individuals. Symptoms generally attribut ed to B. hominis infection are nonspecific, and the need for treatment is debated. If treatment appears warranted, metronidazole is suggeste d as the drug of choice, although failures of this drug in eradicating the organism have been reported. Infection is diagnosed by light micr oscopic examination of stained smears or wet mounts of fecal material. Most laboratories identify B. hominis by observing the vacuolar form, although morphological studies indicate that other forms, such as the cyst form and multivacuolar form, also should be sought for diagnosis .