Cyclospora Species – A New Protozoan Pathogen of Humans

Background: Organisms referred to as “cyanobacterium-like bodies” have 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 young children infected with this organism. We now attempt to identify it. Methods: Fecal samples were collected weekly from the children and examined with the use of acid-fast staining and staining with a monoclonal antibody specific for cryptosporidium. Stools positive for cyanobacterium-like bodies were preserved in potassium dichromate and exposed to conditions allowing coccidian sporulation and excystation. Both unsporulated and sporulated oocysts were fixed by freeze-substitution techniques and then examined by electron microscopy. Results: Organisms isolated from the feces of Peruvian patients and two patients from the United States were identified as belonging to the coccidian genus cyclospora, after sporulation and excystation of the oocysts according to standard techniques. Complete sporulation occurred within 5 to 13 days in oocysts maintained in potassium dichromate at 25 or 32 °C. Complete excystation resulted in the liberation of two sporozoites from the two sporocysts within each oocyst (cryptosporidia have four naked sporozoites within each oocyst). The presence of organelles characteristic of coccidian organisms was confirmed by electron microscopy. Conclusions: We have identified organisms of the genus cyclospora that are remarkably similar to cryptosporidia in their morphologic features and the diarrheal disease that they produce in humans. The complete life cycle and epidemiology of this new protozoan parasite remain to be described., Spherical organisms that are 8 to 10 micrometers in diameter and have variable characteristics on acid-fast staining are being identified with increasing frequency in feces from both immunocompetent visitors to developing countries and immunocompromised patients with chronic diarrhea in the United States¹–⁸. The first reported cases of infection with such organisms attributed the illness to an unsporulated, coccidian body or a fungal spore¹. The patients were immunologically competent, had traveled from the United States to either Mexico or Haiti, and reported a “flu-like” illness accompanied by nausea, vomiting, anorexia, weight loss, and explosive watery diarrhea lasting one…