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Clinical Microbiology Reviews, 10 1996, 563-584, Vol 9, No. 4
DJ Stenzel and PF Boreham
Blastocystis hominis is a unicellular organism found commonly in the
intestinal tract of humans and many other animals. Very little is known of
the basic biology of the organism, and controversy surrounds its taxonomy
and pathogenicity. There morphological forms (vacuolar, granular, and
ameboid) have been recognized, but recent studies have revealed several
additional forms (cyst, avacuolar, and multivacuolar). The biochemistry of
the organism has not been studied to any extent, and organelles and
structures of unknown function and composition are present in the cells.
Several life cycles have been proposed but not experimentally validated.
The form used for transmission has not been defined. Infections with the
organism are worldwide and appear in both immunocompetent and
immunodeficient individuals. Symptoms generally attributed to B. hominis
infection are nonspecific, and the need for treatment is debated. If
treatment appears warranted, metronidazole is suggested as the drug of
choice, although failures of this drug in eradicating the organism have
been reported. Infection is diagnosed by light microscopic 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.
Copyright © 1996 by the American Society for Microbiology. All rights reserved.
Blastocystis hominis revisited
Analytical Electron Microscopy Facility, Queensland University of Technology, Australia.
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