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Cyclospora species--a new protozoan pathogen of humans
Y R Ortega1, C R Sterling, R H Gilman
1Department of Veterinary Science, University of Arizona, Tucson 85721.
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 degrees 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.
Insights
Researchers identified a new coccidian parasite, Cyclospora, causing diarrhea in children. This organism is morphologically similar to Cryptosporidium, highlighting a new cause of diarrheal illness.
Area of Science:
- Medical Parasitology
- Infectious Diseases
- Microbiology
Background:
- Cyanobacterium-like bodies (CLBs) detected globally in diarrheal patients, both immunocompetent and immunocompromised.
- Similar organisms isolated from Peruvian patients since 1985.
- Prospective study of two infant/young child cohorts infected with CLBs from 1988-1991.
Purpose of the Study:
- To identify the causative agent of diarrhea presenting as cyanobacterium-like bodies.
- To differentiate the organism from known pathogens like Cryptosporidium.
Main Methods:
- Fecal samples analyzed using acid-fast staining and Cryptosporidium-specific monoclonal antibody.
- Potassium dichromate preservation for sporulation and excystation.
- Electron microscopy for detailed morphological analysis of oocysts.
Main Results:
- Organisms identified as belonging to the coccidian genus Cyclospora.
- Oocyst sporulation occurred within 5-13 days at 25-32°C in potassium dichromate.
- Excystation revealed two sporocysts, each containing two sporozoites, distinct from Cryptosporidium.
Conclusions:
- Cyclospora identified as a cause of human diarrheal disease, morphologically resembling Cryptosporidium.
- Further research needed to elucidate the complete life cycle and epidemiology of this protozoan parasite.