Molecular diagnosis of cystoisosporiasis using extended-range PCR screening.

The differential diagnosis of diarrhea in immunocompromised patients encompasses many intestinal parasites including the coccidian Cystoisospora belli. Gastrointestinal infection with C. belli leads to cystoisosporiasis with diarrhea and, depending on host immune status, can cause extraintestinal disease. C. belli is usually diagnosed by examination of stool or intestinal biopsy specimens; however, the organism may be undetected using these test methods. Thus, more sensitive molecular tools for detection of pathogenic parasites are desirable. Herein is described a patient with AIDS who had persistent diarrhea of unknown cause. Microscopic examinations of stool and ileal biopsy specimens were initially unremarkable for any specific pathogen. Screening of DNA extracted from biopsy material using extended-range PCR primers recognizing conserved DNA sequences found in many fungi and parasites revealed infection with C. belli, which was confirmed at repeat histologic analysis. Extended-range PCR screening was used because the differential diagnosis was broad and other tools were not applied, yet this molecular approach led to the appropriate diagnosis and treatment of the condition. Thus, this approach offers a promising test for diagnosis of parasitic diseases that elude diagnosis using conventional methods.