近20年中国部分地区鸡源H9N2亚型禽流感病毒HA基因遗传演化及其变异频率

Genetic evolution and substitution frequency of avian influenza virus HA gene in chicken H9N2 subtype in China in the last 20 years

摘要:

【目的】通过比较不同时期的H9N2亚型禽流感流行毒株HA基因的分子特征和变异频率,揭示免疫压力下病毒的遗传演化趋势。【方法】选取源于课题组的40株鸡源H9N2毒株,以及从GenBank下载的136株中国鸡源H9N2流行毒株和7株经典毒株的序列,利用Lasergen 7.1和MEGA 5.1等软件,对其HA基因进行系统演化、分子特征和变异频率分析。【结果】系统发育分析表明,近20年的鸡源H9N2流行株分属于BJ94、Y280和S2等谱系,优势流行株的分布与年代密切相关。氨基酸序列比较显示, H9N2病毒不同谱系之间具有各自的特征,且存在着明显的氨基酸变异积累。以Ck/BJ/1/1994 HA基因为参照,1994-2014年间, H9N2流行株核苷酸和氨基酸的年均进化率分别为5.73×10^-3和4.25×10^-3。其中,2011-2014年的核苷酸(氨基酸)年均进化率为6.35×10^-3(5.32×10^-3),明显高于2006-2010年5.22×10^-3(3.70×10^-3),更显著高于疫苗推广初期1999-2005年的0.74×10^-3(0.50×10^-3)。【结论】 H9N2疫苗株和流行毒株的不匹配是病毒变异频率加快的重要原因。

Abstract:

[Objective] Low pathogenic avian influenza(LPAI) H9N2 subtype virus has been prevalent in domestic poultry in China over two decades. This study was to determine the genetic evolution trend of H9N2 avian influenza virus(AIV) under immune pressure of vaccine.[Methods] H9 HA sequences of 40 isolates from the present study and 136 pandemic strains and 7 classical strains from China downloaded from GenBank, were genetically analyzed to determine evolution, molecular characteristic, and mutation frequency.[Results] Phylogenetic trees analysis suggested that H9N2 subtypes AIV could be clustered into 5 distinct lineages:G1-like, BJ94-like, Y280-like, S2-like and Americans lineages. Most H9N2 isolates in 2005-2014 belonged to S2-like sub-genotype, suggesting that this genotype was the dominate isolates in China. Further more, comparison based on the amino acid sequence showed that different lineages have their distinct characteristics, and significant accumulations of amino acid variation were also found. In addition, in comparison with reference Ck/BJ/1/1994 HA gene, average annual substitution rates of H9N2 pandemic strain nucleotide and amino acid were 5.73×10^-3 and 4.25×10^-3 from 1994 to 2014, respectively. Substitution rate during 2011-2014 were 6.35×10^-3 and 5.32×10^-3, higher than that during the period of 2006-2010(5.22×10^-3 and 3.70×10^-3) and even much higher than that during the 1999-2005(0.74×10^-3and 0.50×10^-3), when the vaccines were initially applied in the field.[Conclusion] Overall, these data indicate that the mismatch between H9N2 vaccine strains and pandemic strains drives the virus to quickly mutate.