Detection of Cyclospora cayetanensis in Food and Water Samples: Optimized Protocols for Specific and Sensitive Molecular Methods from a Regulatory Agency Perspective

Cyclospora cayetanensis is a coccidian parasite of the phylum Apicomplexa that causes cyclosporiasis, a human-specific gastrointestinal disease. Unlike most enteric pathogens, C. cayetanensis does not infect via direct fecal–oral transmission between humans because shed oocysts must be exposed to environmental triggers prior to becoming infectious. The development of specific and sensitive detection methods for C. cayetanensis is crucial to effectively address data gaps and provide regulatory support during outbreak investigations. In this study, new more specific molecular markers for the detection of C. cayetanensis were developed based on updated genomic databases of Apicomplexa mitochondrial sequences. Novel alternative reagents and supplies, as well as optimization protocols, were tested in spiked produce and agricultural water samples. The selected Mit1C primers and probe combined showed at least 13 mismatches to other related species. The new optimized qualitative real-time PCR assay with modifications to sample processing and replacement of discontinued items produced results comparable to the previously validated methods. In conclusion, the new optimized qualitative Mit1C real-time PCR assay demonstrated an increase in its specificity in comparison to other detection methods previously published, while it showed to be robust and as sensitive as the previously validated method at the FDA. This study has also expanded the array of PCR reagents that can be used to detect C. cayetanensis in produce and agricultural water samples and provided several improvements to the method for detection in agricultural water including replacements for discontinued items and a new dialysis filter for water filtration.