Abstract
Background Cyclospora cayetanensis is an emerging coccidian parasite that causes endemic and epidemic diarrheal disease called cyclosporiasis, and this infection is associated with consumption of contaminated produce or water in developed and developing regions. Food-borne outbreaks of cyclosporiasis have occurred almost every year in the USA since the 1990s. Investigations of these outbreaks are currently hampered due to lack of molecular epidemiological tools for trace back analysis. The apicoplast of C. cayetanensis, a relict non-photosynthetic plastid with an independent genome, provides an attractive target to discover sequence polymorphisms useful as genetic markers for detection and trace back analysis of the parasite. Distinct differences in the apicoplast genomes of C. cayetanensis could be useful in designing advanced molecular methods for rapid detection and, subtyping and geographical source attribution, which would aid outbreak investigations and surveillance studies.MethodsTo obtain the genome sequence of the C. cayetanensis apicoplast, we sequenced the C. cayetanensis genomic DNA extracted from clinical stool samples, assembled and annotated a 34,146 bp-long circular sequence, and used this sequence as a reference genome in this study. We compared the genome and the predicted proteome to the data available from other apicomplexan parasites. To initialize the search for genetic markers, we mapped the raw sequence reads from an additional 11 distinct clinical stool samples originating from Nepal, New York, Texas, and Indonesia to the apicoplast reference genome.ResultsWe identified several high quality single nucleotide polymorphisms (SNPs) and small insertion/deletions spanning the apicoplast genome supported by extensive sequencing reads data, and a 30 bp sequence repeat at the terminal spacer region in a Nepalese sample. The predicted proteome consists of 29 core apicomplexan peptides found in most of the apicomplexans. Cluster analysis of these C. cayetanensis apicoplast genomes revealed a familiar pattern of tight grouping with Eimeria and Toxoplasma, separated from distant species such as Plasmodium and Babesia.ConclusionsSNPs and sequence repeats identified in this study may be useful as genetic markers for identification and differentiation of C. cayetanensis isolates found and could facilitate outbreak investigations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1896-4) contains supplementary material, which is available to authorized users.
Highlights
Cyclospora cayetanensis is an emerging coccidian parasite that causes endemic and epidemic diarrheal disease called cyclosporiasis, and this infection is associated with consumption of contaminated produce or water in developed and developing regions
The main body of the apicoplast genome was coded by the 24 kb long contig 312 and the contig 451 constituted the approximately 5.5 kb fragment found as two inverted repeats in the apicoplast genome (Fig. 1)
25 million of whole genome sequencing (WGS) reads from samples NF1 and HCNY were mapped to this draft apicoplast genome using Bowtie2 and a mapping tool implemented in Geneious suite to collect reads targeting apicoplast sequences
Summary
Cyclospora cayetanensis is an emerging coccidian parasite that causes endemic and epidemic diarrheal disease called cyclosporiasis, and this infection is associated with consumption of contaminated produce or water in developed and developing regions. Food-borne outbreaks of cyclosporiasis have occurred almost every year in the USA since the 1990s. Investigations of these outbreaks are currently hampered due to lack of molecular epidemiological tools for trace back analysis. Distinct differences in the apicoplast genomes of C. cayetanensis could be useful in designing advanced molecular methods for rapid detection and, subtyping and geographical source attribution, which would aid outbreak investigations and surveillance studies. It can be difficult to link cases to particular food vehicles and sources, thereby hampering the timely implementation of measures to control and prevent outbreaks. The development of molecular methods for the detection and characterization of C. cayetanensis isolates is a priority for US public health agencies [9]
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