State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, People's Republic of China.
Liaoning Provincial Agricultural Development Service Center, Shenyang, People's Republic of China.
J Virol. 2020 Mar 31;94(8). doi: 10.1128/JVI.01930-19.
Genetic reassortments occurred continuously among multiple subtypes or genotypes of influenza viruses prevalent in pigs. Of note, some reassortant viruses bearing the internal genes of the 2009 pandemic H1N1 (2009/H1N1) virus sporadically caused human infection, which highlights their potential threats to human public health. In this study, we performed phylogenetic analysis on swine influenza viruses (SIVs) circulating in Liaoning Province, China. A total of 22 viruses, including 18 H1N1 and 4 H1N2 viruses, were isolated from 5,750 nasal swabs collected from pigs in slaughterhouses from 2014 to 2016. H1N1 viruses formed four genotypes, which included Eurasian avian-like H1N1 (EA H1N1) and double/triple reassortant H1N1 derived from EA H1N1, 2009/H1N1, and triple reassortant H1N2 (TR H1N2) viruses. H1N1 SIVs with different genotypes and even those within the same genotypes represented different pathogenicities in mice. We further characterized two naturally isolated H1N1 SIVs that had similar viral genomes but differed substantially in their virulence in mice and found that a single amino acid at position 431 in the basic polymerase 2 (PB2) protein significantly affected the viral replication capacity and virulence of these two viruses. Taken together, our findings revealed the diverse genomic origins and virulence of the SIVs prevalent in Liaoning Province during 2014 to 2016, which highlights that continuous surveillance is essential to monitor the evolution of SIVs. We identified a naturally occurring amino acid mutation in the PB2 protein of H1N1 SIVs that impacts the viral replication and virulence in mice by altering the viral polymerase activity. The frequent reassortment among different influenza viruses in pigs adds complexity to the epidemiology of swine influenza. The diverse viral virulence phenotypes underline the need to investigate the possible genetic determinants for evaluating the pandemic potential to human public health. Here, we found that multiple genotypes of influenza viruses cocirculate in the swine population in Liaoning Province, China. Furthermore, we pinpointed a single amino acid at position 431 in the PB2 protein which plays a critical role in the virulence of H1N1 viruses in mice and found that the alteration of viral polymerase activities is the cause of the different virulence. Our study further indicated that the virulence of influenza virus is a polygenic trait, and the newly identified virulence-related residue in the PB2 provides important information for broadening knowledge on the genetic basis of viral virulence of influenza viruses.
遗传重配在猪中流行的多种亚型或基因型流感病毒中持续发生。值得注意的是，一些带有 2009 年大流行 H1N1（2009/H1N1）病毒内部基因的重组病毒偶尔会引起人类感染，这突显了它们对人类公共卫生的潜在威胁。在这项研究中，我们对中国辽宁省流行的猪流感病毒（SIV）进行了系统发育分析。共从 2014 年至 2016 年从屠宰场的 5750 份猪鼻拭子中分离出 22 株病毒，包括 18 株 H1N1 和 4 株 H1N2 病毒。H1N1 病毒形成了 4 种基因型，包括欧亚类禽 H1N1（EA H1N1）和源自 EA H1N1、2009/H1N1 和三重重组 H1N2（TR H1N2）病毒的双重组/三重重组 H1N1 病毒。具有不同基因型的 H1N1 SIV，甚至是同一基因型内的 H1N1 SIV，在小鼠中的致病性也不同。我们进一步鉴定了两种自然分离的 H1N1 SIV，它们具有相似的病毒基因组，但在小鼠中的毒力却有很大差异，发现 PB2 蛋白 431 位的单个氨基酸显著影响了这两种病毒的病毒复制能力和毒力。综上所述，我们的研究结果揭示了 2014 年至 2016 年期间辽宁省流行的 SIV 的不同基因组来源和毒力，这突显了持续监测对于监测 SIV 进化的重要性。我们鉴定了 H1N1 SIV 的 PB2 蛋白中一个自然发生的氨基酸突变，该突变通过改变病毒聚合酶活性，影响病毒在小鼠中的复制和毒力。不同流感病毒在猪中的频繁重组增加了猪流感的流行病学复杂性。不同的病毒毒力表型强调需要研究可能的遗传决定因素，以评估对人类公共卫生的大流行潜力。在这里，我们发现多种基因型的流感病毒在中国辽宁省的猪群中共同流行。此外，我们发现 PB2 蛋白 431 位的单个氨基酸在 H1N1 病毒在小鼠中的毒力中起着关键作用，并发现病毒聚合酶活性的改变是导致不同毒力的原因。我们的研究进一步表明，流感病毒的毒力是一种多基因性状，PB2 中鉴定出的新的与毒力相关的残基为拓宽对流感病毒毒力的遗传基础的认识提供了重要信息。
