Sequence variation in three mitochondrial genes among Gasterophilus intestinalis isolates from two distinct regions in China.

Horse gastrointestinal myiasis caused by larvae of Gasterophilus spp. has a worldwide distribution. However, little information is available on the genetic variation of Gasterophilus spp. at the molecular level. In the present study, sequence variation was examined in three mitochondrial (mt) genes, namely mt cytochrome c oxidase subunit 1 (cox1), NADH dehydrogenase subunits 5 (nad5) and large subunit ribosomal RNA (rrnL), among G. intestinalis isolates originating from Heilongjiang Provience and Xinjiang Uygur Autonomous Region, China. The complete cox1, nad5, and rrnL gene sequences were amplified by PCR separately from adult G. intestinalis individuals and the amplicons were sequenced from both directions. The size of the sequences of cox1, nad5, and rrnL genes was 1539 bp, 1717 bp, and 1321 bp, respectively. The A + T contents of the sequences were 62.7-63.9% (cox1), 70-70.7% (nad5), and 74.5-74.9% (rrnL). The intra-specific sequence variations within G. intestinalis were 0.1-3.1% for cox1, 0.4-3.4% for nad5, and 0.1-1.5% for rrnL. Phylogenetic analyses based on the cox1 sequences using the Bayesian inference indicated that all the G. intestinalis isolates grouped together with high statistical support. These findings demonstrated clearly the usefulness of mt cox1, nad5, and rrnL sequences for the molecular identification and for studying population genetics of G. intestinalis in horses.