区分犬瘟热病毒Asia-Ⅰ型野毒株及疫苗株的AS-PCR方法

犬瘟热是一种接触性传染病，可侵害免疫系统、呼吸系统、消化系统，甚至神经系统，导致全身性的病理变化，对宠物犬、毛皮动物等存在巨大威胁。目前常用的胶体金检测法不能有效区分疫苗免疫与动物自然感染。为建立一种高效准确的鉴别犬瘟热病毒野毒株和疫苗株的检测方法，本试验对从武汉地区收集已确诊犬瘟热的6只犬分离得到的野毒株以及3株广泛使用的CDV疫苗株进行全基因组测序，从氨基酸水平和碱基水平比对分析后，确定H基因为AS-PCR引物设计的靶基因。通过对H基因进行分型，发现武汉地区流行的CDV均为Asia-Ⅰ型，而疫苗株Y2为America-I型，疫苗株Y1和Y3均为America-Ⅱ型。对比179株Asia-Ⅰ型（6株野毒株样品+173株GenBank Asia-Ⅰ型）与3株疫苗株的CDV-H基因序列，采用AS-PCR技术（3'端错配）设计出1对能有效区分犬瘟热Asia-Ⅰ型野毒株和疫苗株的特异性引物，上游引物序列为5'-TTAAATGATAATGACATAGTG-3'，下游引物序列为5'-CCTGGCAAGGCAAGA-3'。结果显示该引物有较强的特异性，6株样品野毒株均可扩增出长894 bp的片段，疫苗株不能扩增，且野毒株的H基因上存在9个较为规律的碱基（氨基酸）变异位点，而疫苗株在第277位氨基酸上均为天冬酰胺，这些变异可能导致N-糖基化位点的增加，从而对犬瘟热病毒疫苗株的毒力产生影响。本研究建立的AS-PCR方法能有效区分犬瘟热疫苗和Asia-Ⅰ型野毒株。

The Establishment of AS-PCR Method to Distinguish Canine Distemper Asia-I Type Wild Strains and Vaccine Strains

Canine distemper (CD) is a contagious disease, which can damage the immune system, respiratory system, digestive system, and even nervous system, leading to systemic pathological changes, and has a huge threat to pet dogs, fur animals, etc. At present, the commonly used colloidal gold test cannot effectively distinguish vaccine immunity from animal natural infection. To establish an efficient and accurate detection method for identifying wild strains and vaccine strains of canine distemper virus(CDV), the whole genome of six canine distemper wild strains isolated from dogs and three widely used CDV vaccine strains collected from Wuhan area were sequenced. After comparing and analyzing the amino acid and the base sequences, the H gene was determined as the target gene for AS-PCR primer design. By genotyping the H gene, it was found that the prevalent CDVs in Wuhan were all Asia-Ⅰ, while the vaccine strain Y2 was America-I, and the vaccine strains Y1 and Y3 were both America-Ⅱ. Comparing the CDV-H gene sequences of 179 Asia-Ⅰtypes (6 wild-type strain samples + 173 GenBank Asia-Ⅰtype stains) and 3 vaccine strains, using AS-PCR technology (3'mismatch) to design a pair of primers. It can effectively distinguish CDV Asia-I wild strain and vaccine strain. The upstream primer sequence is 5'-TTAATATAATAATGACAGTG-3', and the downstream primer sequence is 5'-CCTCAAGGGGCACA-3'. The results showed that the primer had a strong specificity and the wild strains could amplify an 894 bp fragment, while the vaccine strains could not. There are 9 more regular bases (amino acids) variation sites in H gene of wild strain, and the 277th amino acids of all vaccine strains are Asparagine. These mutations may lead to an increase in N-glycosylation sites, which will have an impact on the virulence of canine distemper virus vaccine strains. The AS-PCR method established in this study can effectively distinguish the canine distemper vaccine and Asia-Ⅰwild strains.