农科院特产所首次分离出新型犬细小病毒

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    近日，中国农业科学院特产研究所程世鹏研究员领衔的特种动物病原与免疫团队，在犬细小病毒（CPV）分子流行病学调查上取得进展，国内首次分离鉴定了CPV-2c型病毒，该毒株为VP2蛋白上Ala5Gly突变的变异毒株。相关研究部分结果已在国际专业期刊《Infection, Genetic and Evolution》上发表。

    CPV是引起犬急性出血性胃肠炎和幼犬急性心肌炎的主要病原，1978 年在澳大利亚和加拿大等地同时从患肠炎的病犬中分离获得的，最初命名为CPV-2，此后该病在世界范围内广泛流行，CPV除感染犬、狐狸、狼等犬科动物外，也感染猫、豹、熊、虎等其他多种动物，本病在幼犬中的发病率和死亡率很高。CPV具有较高的变异率，自从1970s出现CPV-2型以来，CPV不断的遗传进化，1979~1980年出现CPV-2a型，1984年出现了CPV-2b型，2000年又出现了CPV-2c型。

    特种动物病原与免疫团队王建科博士小组在首席科学家程世鹏研究员的指导下，对我国北方主要省市的CPV进行大量的流行病学调查，经过基因测序与遗传进化分析表明，我国CPV 4种亚型共同流行，但以CPV-2a型为主；在114株CPV病毒中，CPV-2型、CPV-2a型、CPV-2b型和CPV-2c型分别为2株、57株、25株和30株。序列分析显示我国流行毒株VP2蛋白上集中出现了Ala5Gly，Phe267Tyr，Tyr324Ile和Gln370Ary的突变，其中Phe267Tyr，Tyr324Ile和Gln370Ary是近期在国内或亚洲的CPV中出现的，而Ala5Gly的突变是首次在CPV上出现，也是国内首次对CPV-2c型病毒进行大规模的流行病学调查；系统发育研究表明我国流行毒株与国外毒株遗传距离较远，形成单独的分支（图1）。

    CPV新亚型的出现，对犬的致病性增强，感染宿主范围扩大，免疫犬时常有发病的报道，现有疫苗（CPV2/2b型）是否能保护流行毒株的攻击已成为一个科学问题，本研究分离4个亚型的流行毒株为研制新亚型疫苗及亚型间的交叉保护作用研究奠定了基础。

图1. 北京分离毒株VP2核苷酸系统发育树

Figure 1. Phylogenetic analysis of CPV based on VP2 nucleotide sequences（来源于 农科院特产所网站）

文章题目：Continuing evolution of canine parvovirus in China: Isolation of novel variants with an Ala5Gly mutation in the VP2 protein
文章摘要：Canine parvovirus (CPV) type 2c is a new antigenic variant of CPV-2. Since the year 2000 it has spread to several countries, causing severe hemorrhagic enteritis in dogs. In 2014 and 2015, 58 fecal samples were collected from dogs in Beijing with suspected CPV infection. Regardless of the vaccination status of the dogs, 43 samples were found positive for CPV according to PCR results; i.e., 18, 7, and 18 respectively belonged to antigenic types new CPV-2a, new CPV-2b, and CPV-2c. A phylogenetic tree based on their VP2 gene sequences indicated that the Chinese CPV-2c strains form a separate cluster. In addition to synonymous mutations, the CPV-2c strains also contain a unique coding mutation in VP2 that leads to glycine at residue 5, instead of the highly conserved alanine at this position in all other CPV-2c strains sequenced to date. Using F81 cells, several novel isolates of CPV-2c, each with the Ala5Gly mutation, were obtained. One of these was used to infect experimentally beagle dogs, which subsequently developed the typical clinical symptoms of CPV infection. Hence, it appears that CPV-2c is still evolving in China, a finding that warrants continuous surveying and the eventual adaptation of current vaccines.
文章链接：http://www.sciencedirect.com/science/article/pii/S1567134815300745