Draft Hybrid Genome Assembly of a Canadian Cyclospora cayetanensis Isolate

Evaluation of the Increased Genetic Resolution and Utility for Source Tracking of a Recently Developed Method for Genotyping Cyclospora cayetanensis

Cyclospora cayetanensis is a foodborne parasite that causes cyclosporiasis, an enteric illness in humans. Genotyping methods are used to genetically discriminate between specimens from cyclosporiasis cases and can complement source attribution investigations if the method is sufficiently sensitive for application to food items. A very sensitive targeted amplicon sequencing (TAS) assay for genotyping C. cayetanensis encompassing 52 loci was recently designed. In this study, we analyzed 66 genetically diverse clinical specimens to assess the change in phylogenetic resolution between the TAS assay and a currently employed eight-marker scheme. Of the 52 markers, ≥50 were successfully haplotyped for all specimens, and these results were used to generate a hierarchical cluster dendrogram. Using a previously described statistical approach to dissect hierarchical trees, the 66 specimens resolved into 24 and 27 distinct genetic clusters for the TAS and an 8-loci scheme, respectively. Although the specimen composition of 15 clusters was identical, there were substantial differences between the two dendrograms, highlighting the importance of both inclusion of additional genome coverage and choice of loci to target for genotyping. To evaluate the ability to genetically link contaminated food samples with clinical specimens, C. cayetanensis was genotyped from DNA extracted from raspberries inoculated with fecal specimens. The contaminated raspberry samples were assigned to clusters with the corresponding clinical specimen, demonstrating the utility of the TAS assay for traceback efforts.

The first Cyclospora cayetanensis lineage A genome from an isolate from Mexico

BACKGROUND

Cyclospora cayetanensis is a protozoan parasite that causes intestinal illness in humans worldwide. Despite its global distribution, most genomic data for C. cayetanensis has been obtained from isolates collected in the United States, leaving genetic variability among globally distributed isolates underexplored.

RESULTS

In the present study, the genome of an isolate of C. cayetanensis obtained from a child with diarrhea living in Mexico was sequenced and assembled. Evaluation of the assembly using a lineage typing system recently developed by the Centers for Disease Control and Prevention revealed that this isolate is lineage A.

CONCLUSIONS

Given that the only other whole genome assembly available from Mexico was classified as lineage B, the data presented here represent an important step in expanding our knowledge of the diversity of C. cayetanensis isolates from Mexico at the genomic level.

Hastening Progress in Cyclospora Requires Studying Eimeria Surrogates

Cyclospora cayetanensis is an enigmatic human parasite that sickens thousands of people worldwide. The scarcity of research material and lack of any animal model or cell culture system slows research, denying the produce industry, epidemiologists, and regulatory agencies of tools that might aid diagnosis, risk assessment, and risk abatement. Fortunately, related species offer a strong foundation when used as surrogates to study parasites of this type. Species of Eimeria lend themselves especially well as surrogates for C. cayetanensis. Those Eimeria that infect poultry can be produced in abundance, share many biological features with Cyclospora, pose no risk to the health of researchers, and can be studied in their natural hosts. Here, we overview the actual and potential uses of such surrogates to advance understanding of C. cayetanensis biology, diagnostics, control, and genomics, focusing on opportunities to improve prevention, surveillance, risk assessment, and risk reduction. Studying Eimeria surrogates accelerates progress, closing important research gaps and refining promising tools for producers and food safety regulators to monitor and ameliorate the food safety risks imposed by this emerging, enigmatic parasite.

Genotyping Canadian Cyclospora cayetanensis Isolates to Supplement Cyclosporiasis Outbreak Investigations

Cyclospora cayetanensis is an emerging foodborne parasite that causes cyclosporiasis, an enteric disease of humans. Domestically acquired outbreaks have been reported in Canada every spring or summer since 2013. To date, investigations into the potential sources of infection have relied solely on epidemiological data. To supplement the epidemiological data with genetic information, we genotyped 169 Canadian cyclosporiasis cases from stool specimens collected from 2010 to 2021 using an existing eight-marker targeted amplicon deep (TADS) scheme specific to C. cayetanensis as previously described by the US Centers for Disease Control and Prevention (CDC). This is the first study to genotype Canadian Cyclospora cayetanensis isolates, and it focuses on evaluating the genotyping performance and genetic clustering. Genotyping information was successfully collected with at least part of one of the markers in the TADS assay for 97.9% of specimens, and 81.1% of cyclosporiasis cases met the minimum requirements to genetically cluster into 20 groups. The performance of the scheme suggests that examining cyclosporiasis cases genetically will be a valuable tool for supplementing epidemiological outbreak investigations and to minimize further infections. Further research is required to expand the number of discriminatory markers to improve genetic clustering.