Isosporosis and unizoite tissue cysts in patients with acquired immunodeficiency syndrome

Isospora belli, a coccidian parasite in humans, has been described as causi ng chronic diarrhea and acalculous cholecystitis in patients with the acqui red immunodeficiency syndrome (AIDS). Diagnosis can be made at the tissue l evel in the epithelium of the small bowel and by fecal examination. Dissemi nated extraintestinal forms are uncommon. We studied 118 adult patients wit h AIDS and chronic diarrhea using stool analysis and endoscopy with duodena l biopsy specimen collection. These samples were processed by routine histo logy and transmission electron microscopy. Isosporosis was diagnosed in 8 E ases. In 2 of them, unizoite tissue cysts were present in the lamina propri a, with negative results in stool materials. The cysts were located within a large parasitophorous vacuole, There were no structural means of differen tiating the species level of Isospora based on morphology using light or el ectron microscopy. We believe further work should be done to determine if u nizoite tissue cysts are part of the cycle of I belli or of other species o f Isospora that could be pathogenic in immunocompromised hosts. Copyright ( C) 2001 by W.B. Saunders Company.