新城疫弱毒活疫苗中FAdV-4的分离鉴定及分子特征

Identification and molecular characteristic of fowl adenovirus serotype 4 isolated from a live newcastle disease virus vaccine

摘要:

【目的】当前我国鸡群禽腺病毒(Fowl adenovirus，FAdV)感染严重，该病毒既可水平传播也可经卵垂直传播，因此鸡胚源禽用弱毒活疫苗是否存在FAdV污染，进而造成疫病的传播尚不清楚。检测我国商品化新城疫La Sota弱毒活疫苗中是否存在FAdV污染，探讨国内鸡群中FAdV感染和流行的可能原因。【方法】应用本实验室建立的FAdV PCR检测方法检测商品化新城疫La Sota弱毒活疫苗，并进行FAdV分离鉴定。经序列比对和进化分析，鉴定分离毒株所属种、血清型及进化特征。【结果】分离到一株禽腺病毒，命名为L160962。基因分析表明，分离株L160962的52k和hexon基因片段序列与C种内的血清4型毒株相似性最高，其中与中国毒株HN/151025和CH/HNJZ/2015的相似性为99.9%?100%，与奥地利毒株KR5的相似性为99.3%，但与A、B、D和E种FAdV的相似性分别为79.0%?83.3%。系统进化分析表明，L160962与C种内的血清4型禽腺病毒在同一分支，核苷酸相似性在99.9%以上，应划分为血清4型FAdV。基于分离株L160962的hexon基因构建的系统进化树的拓扑结构，分离株L160962与中国毒株亲缘关系最近，提示疫苗源分离株L160962与我国当前流行毒株相近。【结论】我国商品化的新城疫La Sota弱毒活疫苗中存在血清4型FAdV污染，这可能是我国鸡群中FAdV大面积感染和流行的原因之一。

Abstract:

[Objective] Fowl adenovirus (FAdV) infection in chicken flocks is very common in China currently. Because FAdV transmits both horizontally and vertically in chickens, it is essential and urgent to determine the contamination of attenuated vaccines produced in chicken embryo eggs by FAdV and its risk to induce epidemic of Hepatitis-Hydropericardium syndrome (HHS) caused by FAdV. The objectives were to ascertain the contamination of an attenuated live Newcastle disease virus (NDV) vaccine produced by Chinese veterinary drug company by FAdV and to investigate the possible reasons for current prevalence of HHS caused by FAdV in chicken flocks in China. [Methods] FAdV-specific PCR was employed to detect FAdV from the attenuated live vaccine of NDV La Sota strain. PCR positive samples were inoculated into chicken embryo eggs for the isolation of FAdV. Sequencing, identity analysis and the phylogenetic tree construction were performed to analyze the molecular characteristics, genotyping and serotyping of the isolates. [Results] A FAdV strain was obtained and named L160962 that shared the highest identity with serotype 4 FAdVs in the 52k and hexon genes according to homology analysis. Among the strains investigated, isolate L160962 shared identities at a level of 99.9%?100% with Chinese strains HN/151025 and CH/HNJZ/2015, 99.3% with Austrian strain KR5, and only 79.0%?83.3% with members in species A, B, D and E in the sequences of 52k and hexon. Phylogenetic analysis showed that isolate L160962 was clustered into serotype 4 within the species C with an identity higher than 99.9% and most close to the Chinese strains, suggesting that isolate L160962 is similar to the prevalent strains in China. [Conclusion] Our studies observed contamination of attenuated vaccines produced in chicken embryo eggs by serotype 4 of FAdV, which may be one of the reasons that lead to FAdV infection prevalent in chicken flocks in China.