Samuel Miño, Laura Mojsiejczuk, Wei Guo, Haili Zhang, Ting Qi, Cheng Du, Xiang Zhang, Jingfei Wang, Rodolfo Campos, Xiaojun Wang
J Virol. 2019 Apr 24. pii: JVI.00116-19. doi: 10.1128/JVI.00116-19. [Epub ahead of print]
Equine influenza virus (EIV) causes severe acute respiratory disease in horses. Currently, the strains belonging to the H3N8 genotype are divided into two clades, Florida clade 1 (FC1) and Florida clade 2 (FC2) which emerged in 2002. Both FC1and 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 separated and divergent lineages, without evidence of reassortment between the clades. While FC1 evolved as a single lineage, the FC2 showed a divergent event around 2004 giving rise to two well supported and coexisting sub-lineages, 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, being the Asian isolates genetically similar to the contemporary American lineages. On the other hand, the FC2 strains detected in Asian mainland countries conformed an autochthonous monophyletic group with a common ancestor dated in 2006 and showed evidence of an endemic circulation in 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 to antigenic sites. Further studies are needed to assess the potential impact of these antigenic changes in vaccination programs.IMPORTANCE The complex and continuous antigenic evolution of 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 horse industry and to help with the selection of the viral strains to be included in the formulation of future vaccines.
Copyright © 2019 American Society for Microbiology.