Department of Paediatric Infectious Diseases, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan.
National Institute of Hygiene and Epidemiology, Hanoi 100000, Viet Nam.
Infect Genet Evol. 2020 Jul;81:104264. doi: 10.1016/j.meegid.2020.104264. Epub 2020 Feb 24.
Influenza virus B belongs to the family Orthomyxoviridae with segmented negative-sense RNA genomes. Since 1970s, influenza B has diverged intoVictoria and Yamagata, which differs in antigenic and evolutionary characteristics. Yet, molecular-epidemiological information of influenza B from developing nations is limited. In central Vietnam, influenza A subtype-specific circulation pattern and clinical characteristics were previously described. However, molecular evolutionary characteristics of influenza B has not been discussed to date. We utilized the influenza B positives obtained from paediatric ARI surveillance during 2007-2013. Influenza B HA and NA genes were amplified, sequenced, and phylogenetic/molecular evolutionary analysis was performed using Maximum Likelihood and Bayesian MCMC. Phylodynamics analysis was performed with Bayesian Skyline Plot (BSP). Furthermore, we performed selection pressure analysis and estimated N-glycosylation sites. In the current study, overall positive rate for influenza B was 3.0%, and Victoria lineage immediately became predominant in post-A/H1N1pdm09 period. The noticeable shift in Victoria lineage WHO Group occurred. With respect to the evolutionary rate (substitutions/site/year), Victoria lineage HA gene was evolving faster than Yamagata lineage (2.43 × 10 vs 2.00 × 10). Furthermore, the evolutionary rate of Victoria Group 5 was greater than Group 1. BSP presented the rapid growth in Effective Population Size (EPS) of Victoria lineage occurred soon after the 1st A/H1N1pdm09 case was detected whereas the EPS of Yamagata lineage was stable for both genes. N-glycosylation pattern between lineages and among WHO Groups were slightly different, and HA gene had a total of 6 amino acid substitutions under positive section pressure (4 for Victoria and 2 for Yamagata). The current results highlight the importance of Victoria lineage in post-A/H1N1pdm09 period. Difference in evolutionary characteristics and phylodynamics may indicate lineage and WHO Group-specific evolutionary dynamics. It is necessary to further continue the molecular-epidemiological surveillance in local setting to gain a better understanding of local evolutionary characteristics of influenza B strains.
乙型流感病毒属于正粘病毒科，具有分段的负义 RNA 基因组。自 20 世纪 70 年代以来，乙型流感已经分化为维多利亚和 Yamagata 谱系，它们在抗原性和进化特征上有所不同。然而，发展中国家乙型流感的分子流行病学信息有限。在越南中部，以前曾描述过甲型流感亚型的循环模式和临床特征。但是，迄今为止尚未讨论乙型流感的分子进化特征。我们利用 2007-2013 年小儿急性呼吸道感染监测中获得的乙型流感阳性样本。扩增、测序了乙型流感 HA 和 NA 基因，并使用最大似然法和贝叶斯 MCMC 进行了系统发育/分子进化分析。使用贝叶斯天际线图（BSP）进行了系统发育动力学分析。此外，我们进行了选择压力分析并估计了 N-糖基化位点。在本研究中，乙型流感的总体阳性率为 3.0%，并且在 A/H1N1pdm09 后，维多利亚谱系立即成为主要谱系。WHO 组的维多利亚谱系发生了明显的转变。就进化率（替换/位点/年）而言，乙型流感 HA 基因比 Yamagata 谱系进化得更快（2.43×10 比 2.00×10）。此外，维多利亚组 5 的进化率大于组 1。BSP 显示，自首次检测到 A/H1N1pdm09 病例以来，维多利亚谱系的有效种群数量（EPS）迅速增加，而 Yamagata 谱系的 EPS 两种基因均保持稳定。谱系之间和 WHO 组之间的 N-糖基化模式略有不同，HA 基因在正选择区域共有 6 个氨基酸替换（4 个为维多利亚，2 个为 Yamagata）。目前的结果强调了维多利亚谱系在 A/H1N1pdm09 后时期的重要性。进化特征和系统发育动力学的差异可能表明谱系和 WHO 组的特定进化动态。有必要在当地环境中继续进行分子流行病学监测，以更好地了解当地乙型流感病毒株的进化特征。
