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Molecular phylogenetic analysis of Cyclospora, the human intestinal pathogen, suggests that it is closely related to
D A Relman1, T M Schmidt, A Gajadhar
1Department of Medicine, Stanford University School of Medicine, California, USA.
Abstract:
A coccidian organism assigned to the genus Cyclospora has been increasingly recognized in association with prolonged diarrhea in humans throughout the world. Confusion surrounds the taxonomy of this fastidious organism, despite the availability of morphology and sporulation characteristics. The small subunit rRNA coding region from cyclosporan oocysts purified from a human fecal specimen was amplified and sequenced. The same sequence was present in specimens from 8 other patients with cyclosporan oocysts but absent in specimens from asymptomatic subjects and from cryptosporidiosis patients. Phylogenetic analysis of rDNA sequences reveals that the human-associated Cyclospora is closely related to members of the Eimeria genus. These results allow predictions concerning Cyclospora host specificity, life cycle, and epidemiology as well as the development of a specific polymerase chain reaction-based diagnostic assay.
Insights
This study identifies the human Cyclospora parasite using molecular sequencing, revealing its close relation to Eimeria. This finding aids in understanding Cyclospora
Area of Science:
- Medical Parasitology
- Molecular Biology
- Infectious Diseases
Background:
- Cyclospora is a coccidian parasite increasingly linked to prolonged human diarrhea globally.
- Taxonomic classification of Cyclospora remains challenging despite morphological data.
Purpose of the Study:
- To molecularly characterize the human-associated Cyclospora species.
- To clarify the phylogenetic position of human Cyclospora.
- To facilitate the development of diagnostic tools.
Main Methods:
- Amplification and sequencing of the small subunit ribosomal RNA (rRNA) gene from Cyclospora oocysts.
- Phylogenetic analysis of obtained rDNA sequences.
- Comparison of sequences from infected patients, asymptomatic subjects, and cryptosporidiosis patients.
Main Results:
- A distinct small subunit rRNA sequence was identified in human Cyclospora oocysts.
- This sequence was consistently found in infected individuals but not in controls.
- Phylogenetic analysis placed human Cyclospora as closely related to the Eimeria genus.
Conclusions:
- Molecular data provides a robust method for identifying human Cyclospora.
- The genetic relationship to Eimeria offers insights into Cyclospora's biology and epidemiology.
- These findings support the development of targeted diagnostic assays, such as polymerase chain reaction (PCR).