State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, People's Republic of China
Instituto Nacional de Tecnología Agropecuaria (INTA), Instituto de Virología, Buenos Aires, Argentina.
J Virol. 2019 Jun 14;93(13). doi: 10.1128/JVI.00116-19. Print 2019 Jul 1.
Equine influenza virus (EIV) causes severe acute respiratory disease in horses. Currently, the strains belonging to the H3N8 subtype are divided into two clades, Florida clade 1 (FC1) and Florida clade 2 (FC2), which emerged in 2002. Both FC1 and FC2 clades were reported in Asian and Middle East countries in the last decade. In this study, we described the evolution, epidemiology, and molecular characteristic of the EIV lineages, with focus on those detected in Asia from 2007 to 2017. The full genome phylogeny showed that FC1 and FC2 constituted separate and divergent lineages, without evidence of reassortment between the clades. While FC1 evolved as a single lineage, FC2 showed a divergent event around 2004 giving rise to two well-supported and coexisting sublineages, European and Asian. Furthermore, two different spread patterns of EIV in Asian countries were identified. The FC1 outbreaks were caused by independent introductions of EIV from the Americas, with the Asian isolates genetically similar to the contemporary American lineages. On the other hand, the FC2 strains detected in Asian mainland countries conformed to an autochthonous monophyletic group with a common ancestor dated in 2006 and showed evidence of an endemic circulation in a local host. Characteristic aminoacidic signature patterns were detected in all viral proteins in both Asian-FC1 and FC2 populations. Several changes were located at the top of the HA1 protein, inside or near antigenic sites. Further studies are needed to assess the potential impact of these antigenic changes in vaccination programs. The complex and continuous antigenic evolution of equine influenza viruses (EIVs) remains a major hurdle for vaccine development and the design of effective immunization programs. The present study provides a comprehensive analysis showing the EIV evolutionary dynamics, including the spread and circulation within the Asian continent and its relationship to global EIV populations over a 10-year period. Moreover, we provide a better understanding of EIV molecular evolution in Asian countries and its consequences on the antigenicity. The study underscores the association between the global horse movement and the circulation of EIV in this region. Understanding EIV evolution is imperative in order to mitigate the risk of outbreaks affecting the horse industry and to help with the selection of the viral strains to be included in the formulation of future vaccines.
马流感病毒（EIV）可引起马的急性呼吸道疾病。目前，属于 H3N8 亚型的菌株分为两个分支，佛罗里达 1 分支（FC1）和佛罗里达 2 分支（FC2），它们分别于 2002 年出现。在过去十年中，亚洲和中东国家都报告了这两个分支。在本研究中，我们描述了 EIV 谱系的进化、流行病学和分子特征，重点关注 2007 年至 2017 年在亚洲检测到的那些谱系。全基因组系统发育表明，FC1 和 FC2 构成了单独且分化的谱系，没有证据表明两个分支之间存在重组。虽然 FC1 作为一个单一谱系进化，但 FC2 在 2004 年左右发生了一个分化事件，产生了两个得到很好支持并共存的亚谱系，欧洲和亚洲。此外，还确定了亚洲国家中两种不同的 EIV 传播模式。FC1 暴发是由从美洲独立引入 EIV 引起的，亚洲分离株与当代美洲谱系在基因上相似。另一方面，在亚洲大陆国家检测到的 FC2 株符合一个具有共同祖先的本土单系群，该共同祖先是在 2006 年，并显示出在当地宿主中地方性循环的证据。在两个亚洲-FC1 和 FC2 群体的所有病毒蛋白中都检测到特征性的氨基酸签名模式。在 HA1 蛋白的顶部、内部或附近的抗原位点都有几个变化。需要进一步研究以评估这些抗原变化对疫苗接种计划的潜在影响。马流感病毒（EIV）的复杂和持续抗原进化仍然是疫苗开发和有效免疫计划设计的主要障碍。本研究提供了一个全面的分析，展示了 EIV 的进化动态，包括在亚洲大陆的传播和循环及其与全球 EIV 种群的关系，为期 10 年。此外，我们更好地了解了亚洲国家 EIV 的分子进化及其对抗原性的影响。该研究强调了全球马运动与该地区 EIV 循环之间的联系。了解 EIV 的进化对于减轻影响马业的暴发风险以及帮助选择未来疫苗中包含的病毒株至关重要。
