Phylogenetic relationships in three species of canine Demodex mite based on partial sequences of mitochondrial 16S rDNA

Background- The historical classification of Demodex mites has been based on their hosts and morphological features. Genome sequencing has proved to be a very effective taxonomic tool in phylogenetic studies and has been applied in the classification of Demodex. Mitochondrial 16S rDNA has been demonstrated to be an especially useful marker to establish phylogenetic relationships. Hypothesis/Objectives- To amplify and sequence a segment of the mitochondrial 16S rDNA from Demodex canis and Demodex injai, as well as from the short-bodied mite called, unofficially, D. cornei and to determine their genetic proximity. Methods- Demodex mites were examined microscopically and classified as Demodex folliculorum (one sample), D. canis (four samples), D. injai (two samples) or the short-bodied species D. cornei (three samples). DNA was extracted, and a 338bp fragment of the 16S rDNA was amplified and sequenced. Results- The sequences of the four D. canis mites were identical and shared 99.6 and 97.3% identity with two D. canis sequences available at GenBank. The sequences of the D. cornei isolates were identical and showed 97.8, 98.2 and 99.6% identity with the D. canis isolates. The sequences of the two D. injai isolates were also identical and showed 76.6% identity with the D. canis sequence. Conclusion- Demodex canis and D. injai are two different species, with a genetic distance of 23.3%. It would seem that the short-bodied Demodex mite D. cornei is a morphological variant of D. canis. © 2012 The Authors. Veterinary Dermatology © 2012 ESVD and ACVD.