CYCLOSPORA SPECIES - A NEW PROTOZOAN PATHOGEN OF HUMANS

Background. Organisms referred to as ''cyanobacterium-like bodies'' ha ve now been identified worldwide in the feces of both immunocompetent and immunocompromised patients with diarrhea. Organisms with a similar appearance have been isolated from Peruvian patients since 1985. From 1988 to 1991 we studied prospectively two cohorts of infants and youn g children infected with this organism. We now attempt to identify it. Methods. Fecal samples were collected weekly from the children and ex amined with the use of acid-fast staining and staining with a monoclon al antibody specific for cryptosporidium. Stools positive for cyanobac terium-like bodies were preserved in potassium dichromate and exposed to conditions allowing coccidian sporulation and excystation. Both uns porulated and sporulated oocysts were fixed by freeze-substitution tec hniques and then examined by electron microscopy.Results. Organisms is olated from the feces of Peruvian patients and two patients from the U nited States were identified as belonging to the coccidian genus cyclo spora, after sporulation and excystation of the oocysts according to s tandard techniques. Complete sporulation occurred within 5 to 13 days in oocysts maintained in potassium dichromate at 25 or 32-degrees-C. C omplete excystation resulted in the liberation of two sporozoites f ro m the two sporocysts within each oocyst (cryptosporidia have four nake d sporozoites within each oocyst). The presence of organelles characte ristic of coccidian organisms was confirmed by electron microscopy. Co nclusions. We have identified organisms of the genus cyclospora that a re remarkably similar to cryptosporidia in their morphologic features and the diarrheal disease that they produce in humans. The complete li fe cycle and epidemiology of this new protozoan parasite remain to be described.