目的 了解山西省绵羊捻转血矛线虫的感染现状及遗传变异情况。方法 采集山西省晋北的山阴县、晋中的祁县和晋南的稷山县绵羊粪样，并提取粪样基因组DNA。利用捻转血矛线虫种特异性引物，扩增样品的核糖体内转录间隔区-2（ITS-2）部分序列，经凝胶电泳观察和DNA测序分析鉴定其种属，评估不同地区绵羊捻转血矛线虫的感染现状。取PCR阳性样品，采用扩增捻转血矛线虫ITS全长序列的保守引物，PCR扩增ITS全长序列并测序，在DNAMAN 9.0中与GenBank中已公开的捻转血矛线虫ITS-2和ITS全长序列进行比对，查找碱基变异位点。使用DNAstar 7.1软件计算捻转血矛线虫ITS序列的碱基含量，并对GenBank中已报道的不同地区、不同宿主来源的18条捻转血矛线虫ITS全长序列及本研究获得的2条ITS全长序列进行序列相似性分析，用最大似然法构建基于ITS全长序列的系统进化树，分析捻转血矛线虫的遗传变异情况。结果 共采集401份绵羊粪样，其中69份粪样扩增出ITS-2片段（占17.2%）；序列分析结果显示，获得的ITS-2部分序列与捻转血矛线虫（GenBank登录号OQ674251）的序列相似性为100%，故鉴定为捻转血矛线虫。其中山阴县、稷山县和祁县的绵羊捻转血矛线虫阳性率分别为47.4%（64/135）、3.0%（5/169）和0（0/97）。69份ITS-2阳性的粪样中，4份样品成功扩增出ITS全长序列，其存在两种基因型，且这两种基因型之间仅在ITS-1序列中226 bp处存在1个碱基差异。基于捻转血矛线虫ITS全长序列的序列相似性分析发现，两种基因型之间的变异率仅为0.1%；18条不同地区和不同宿主来源的捻转血矛线虫的序列间变异率为0~2.6%。系统进化树分析结果显示，本研究中鉴定的序列（GenBank登录号OP518297和OP518298）与来自美国（GenBank登录号EU086378）、老挝（GenBank登录号AB908961）和中国其他地区（GenBank登录号HQ844231）的序列处于同一分支上；捻转血矛线虫的群体遗传结构无明显的地理和宿主相关性。结论 山西省调查地区的绵羊捻转血矛线虫感染率较高，捻转血矛线虫的遗传变异率较低，与其他地区、不同宿主来源的捻转血矛线虫之间无明显差异。

Objective To understand the prevalence and genetic variation of Haemonchus contortus in sheep in Shanxi Province. Methods Fecal samples were collected from sheep in Shanyin County in Northern Shanxi, Qi County in Central Shanxi and Jishan County in Southern Shanxi for extraction of genomic DNA, of which the partial sequence of H. contortus second internal transcribed spacer 2 (ITS-2) was amplified using H. contortus specific primers by PCR and sequenced to identify the parasite species by gel electrophoresis and evaluate the H. contortus prevalence in sheep in different regions of Shanxi Province. The full-length sequence of ITS of H. contortus was amplified by PCR using conserved primers from ITS-2 positive samples and was sequenced. The ITS-2 sequences and ITS full-length sequences of H. contortus obtained in this study were aligned with the corresponding sequences available in GenBank to examine the base mutation site by DNAMAN 9.0. The base content of H. contortus ITS sequence was calculated using DNAstar 7.1 software. Moreover, the sequence homolohy was analyzed on 18 ITS full-length sequences of H. contortus from different regions and hosts, which were available in GenBank (n = 18), and the 2 ITS full-length sequences obtained in this study. Based on the ITS full-length sequence, phylogenetic tree was constructed using maximum likelihood method to analyze the genetic variation in H. contortus. Results A total of 401 sheep fecal samples were collected, of which 69 samples were successfully amplified with the target ITS-2 fragment (17.2%). The ITS-2 sequences obtained in this study showed 100% sequence identity with that of H. contortus (accession number OQ674251) and were identified as H. contortus. The positive rate of H. contortus was 47.4% (64/135), 3.0% (5/169) and 0 (0/97) in sheep in Shanyin County, Jishan County and Qi County of Shanxi Province, respectively. In addition, the complete ITS sequences of H. contortus were successfully amplified from 4 H. contortus-positive fecal samples, showing two genotypes with a single nucleotide variation at the 226 bp position of ITS-1 locus. Based on the sequence identity analysis of the complete ITS sequences of H. contortus, it was found that the variation rate between the two genotypes identified in this study was only 0.1%, and the variation rate of the 18 sequences from different regions of the world and hosts were 0-2.6%. The analysis of ITS sequences and phylogenetic tree showed that the sequences identified in this study, OP518297 and OP518298, were on the same branch with sequences from the United States (accession number EU086378), Laos (accession number AB908961) and other regions of China (accession number HQ844231), and there was no significant difference among ITS sequences of H. contortus from different regions of the world and hosts. Conclusion The H. contortus infection rate in sheep in the surveyed regions of Shanxi Province was comparatively high, while the genetic variation rate of the parasite detected was low, which showed no significant difference from those of H. contortus found in different regions and hosts.