Molecular identification of four phenotypes of human Demodex in China

Traditional classification of Demodex mites by hosts and phenotypic characteristics is defective because of environmental influences. In this study, we proposed molecular identification of four phenotypes of two human Demodex species based on mitochondrial cox1 fragments for the first time. Mites collected from sufferers' facial skin were classified into four phenotypes: phenotype A-C with finger-like terminus, and phenotype D with cone-like terminus. The results of molecular data showed that cox1 sequences were all 429 bp. Divergences, genetic distances and transition/transversion ratios among the three phenotypes with finger-like terminus were 0.0-3.0%, 0.000-0.031, and 6/3-5/0, respectively, in line with intraspecific differences. However, those measures between the phenotype with cone-like terminus and phenotypes with finger-like terminus were 19.6-20.5%, 0.256-0.271, and 0.58 (31/53)-0.66 (35/53), respectively, reaching interspecific level. Phylogenetic trees also showed that the three phenotypes with finger-like terminus clustered as one clade, and the phenotype with cone-like terminus formed another one. Therefore, we conclude that mitochondrial cox1 sequence is a good marker for identification of two human Demodex species. Molecular data indicate no subspecies differentiation. Terminus is an effective character for species identification. Mites with finger-like terminus are Demodex folliculorum, and those with cone-like terminus are Demodex brevis.