Several reports have appeared recently in the literature detailing cases in which gastrointestinal (GI) disease, often with significant associated morbidity, occurred in AIDS patients infected with microsporidial parasites. Consequently, awareness has increased among clinicians as to the potential importance of microsporidia as GI pathogens. Attention is now being focused on methods for diagnosis and treatment. There is considerable interest in determining the diagnostic value of stool specimens for detecting GI disease caused by microsporidia, and a variety of staining modalities have been evaluated. Unfortunately, the various species of microsporidia that infect humans can only be identified accurately by visualizing characteristic subcellular morphologic features of organisms in electron micrographs of tissue specimens. Because the efficacy of treatment regimens currently in development may be somewhat species-specific and because invasive procedures are necessary to obtain appropriate specimens for electron microscopy (EM), a more widely available approach to identification than EM is clearly required. We have developed a polymerase chain reaction (PCR) assay for amplification of microsporidial rRNA genes followed by restriction endonuclease digestion of PCR products to identify microsporidia in fresh stool. The PCR primers used in the assay will amplify all the currently identified microsporidial human pathogens. The assay is being modified to allow detection of microsporidia in formalin-fixed stool specimens. A dot-blot format using PCR-amplified DNA and species-specific DNA probes will be evaluated for identification of microsporidial species.
