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The roundworms of genus Strongylus are the common parasitic nematodes in the large intestine of equine, causing significant economic losses to the livestock industries. In spite of its importance, the genetic data and epidemiology of this parasite are not entirely understood. In the present study, the complete S. equinus mitochondrial (mt) genome was determined. The length of S. equinus mt genome DNA sequence is 14,545 bp, containing 36 genes, of which 12 code for protein, 22 for transfer RNA, and two for ribosomal RNA, but lacks atp 8 gene. All 36 genes are encoded in the same direction which is consistent with all other Chromadorea nematode mtDNAs published to date. Phylogenetic analysis based on concatenated amino acid sequence data of all 12 protein-coding genes showed that there were two large branches in the Strongyloidea nematodes, and S. equinus is genetically closer to S. vulgaris than to Cylicocyclus insignis in Strongylidae. This new mt genome provides a source of genetic markers for the molecular phylogeny and population genetics of equine strongyles. [ABSTRACT FROM AUTHOR]

The equine pinworm Oxyuris equi (Nematoda: Oxyuridomorpha) is the most common horse nematode, has a worldwide distribution, and causes major economic losses. In the present study, the complete O. equi mitochondrial (mt) genome was sequenced, and the mt genome structure and organization were compared with those of other closely related pinworm species, Enterobius vermicularis and Wellcomia siamensis . The O. equi mt genome is a 13,641-bp circular DNA molecule that encodes 36 genes (12 protein-coding genes, 22 tRNAs, and two rRNAs) and one non-coding region, which is slightly shorter than that of E. vermicularis and W. siamensis . The O. equi mt gene arrangement was consistent with that of GA13-type E. vermicularis but it differs from GA12-type W. siamensis . Phylogenetic analyses using concatenated amino acid sequences of the 12 protein-coding genes with three different computational algorithms (maximum parsimony, maximum likelihood, and Bayesian inference) revealed that there were two distinct clades in Chromadorea nematodes that reflected infraorder. Spiruromorpha formed one clade, whereas Rhabditomorpha, Ascaridomorpha, and Oxyuridomorpha formed another clade. O. equi , E. vermicularis , and W. siamensis represent distinct but closely related species, which indicated that Oxyuridomorpha is paraphyletic. Sequencing the O. equi mt genome provides novel genetic markers for studying the molecular epidemiology and population genetics of pinworms. [ABSTRACT FROM AUTHOR]