Department of Immunology and Pathogen Biology, College of Medicine, Xi'an Jiaotong University, No.76 Yanta West Road, Xi'an, China, 710061,
Parasitol Res. 2013 Nov;112(11):3703-11. doi: 10.1007/s00436-013-3558-1. Epub 2013 Aug 15.
Classification of Demodex mites has long depended on hosts and morphological characteristics. However, the fact that two species coexist in the same host and phenotype is easily influenced by environment causes difficulty and indeterminacy in traditional classification. Genotype, which directly reflects the molecular structure characteristics, is relatively stable. In this study, species identification of four phenotypes of human Demodex mites was conducted. Mites were morphologically classified into four phenotypes: long- and short-bodied Demodex folliculorum with finger-like terminus and Demodex brevis with finger- or cone-like terminus. The mitochondrial 16S ribosomal DNA (rDNA) fragment of individual mite was amplified, cloned, sequenced, and aligned. Sequence divergences, genetic distances, transition/transversion rates, and phylogenetic trees were analyzed. The results demonstrated that the 16S rDNA sequence of three phenotypes with finger-like terminus was 337 bp, and that of phenotype with cone-like terminus was 342 bp. The divergences, genetic distances, and transition/transversion rates among the three phenotypes with finger-like terminus were 0.0-2.7%, 0.000-0.029, and 5.0-7/0 (5/1-7/0), respectively, indicating an intraspecific variation. Yet, those between these three phenotypes and the one with cone-like terminus were 21.6-22.8%, 2.510-2.589, and 0.47-0.59 (22/47-27/46), respectively, suggesting an interspecific variation. The five phylogenetic trees showed that the three phenotypes with finger-like terminus clustered into one branch, while the phenotype with cone-like terminus clustered into another. In conclusion, terminus is a major morphological characteristic for the identification of human Demodex species. The three phenotypes with finger-like terminus belong to D. folliculorum, while the phenotype with cone-like terminus belongs to D. brevis. Molecular identification can verify and replenish morphological identification.
蠕形螨的分类长期以来一直依赖于宿主和形态特征。然而，由于两种物种在同一宿主和表型中共存，并且容易受到环境的影响，这给传统的分类带来了困难和不确定性。基因型直接反映分子结构特征，相对稳定。本研究对 4 种人蠕形螨表型进行了种属鉴定。根据形态学将螨虫分为 4 种表型：长体和短体毛囊蠕形螨末端呈指状，短体蠕形螨末端呈指状或锥状。扩增、克隆、测序并比对个体螨的线粒体 16S 核糖体 DNA（rDNA）片段。分析序列分歧、遗传距离、转换/颠换率和系统发育树。结果表明，3 种末端呈指状表型的 16S rDNA 序列为 337bp，末端呈锥状表型的 16S rDNA 序列为 342bp。3 种末端呈指状表型之间的分歧、遗传距离和转换/颠换率分别为 0.0-2.7%、0.000-0.029 和 5.0-7/0（5/1-7/0），表明种内变异。而这三种表型与末端呈锥状表型之间的差异分别为 21.6-22.8%、2.510-2.589 和 0.47-0.59（22/47-27/46），表明种间变异。5 个系统发育树表明，3 种末端呈指状表型聚为一支，而末端呈锥状表型聚为另一支。总之，末端是鉴定人蠕形螨种属的主要形态特征。3 种末端呈指状表型属于毛囊蠕形螨，而末端呈锥状表型属于短体蠕形螨。分子鉴定可以验证和补充形态鉴定。
