Molecular analyses of H3N2 canine influenza viruses isolated from Korea during 2013-2014

Abstract

Canine influenza A virus (CIV) causes a respiratory disease among dog populations and is prevalent in North America and Asia. Recently, Asian H3N2 CIV infection has been of particular concern, with recent reports related to reassortants with pandemic 2009 strains, direct transmission from a human H3N2, a possibility of H3N2 CIV transmission to other mammals, and even the first outbreak of H3N2 CIVs in North America in April 2015. However, despite these global concerns, our understanding of how influenza A virus transmission impacts the overall populations of H3N2 CIVs remains incomplete. Hence, we investigated the evolutionary history of the most recent two Korean CIV isolates, A/canine/Korea/BD-1/2013 and A/canine/Korea/DG1/2014, along with 57 worldwide CIVs, using comprehensive molecular analyses based on genomic genotyping. This study presents that the new Korean CIV isolates are closely related to the predominantly circulating H3N2 CIVs with genotypes K, G, E, 3B, F, 2D, F, and 1E, carrying several mutations in antigenic and host determinant sites. Also, our findings show that the genome-wide genetic variations within the H3N2 CIVs are low; however, two antigenic protein (HA and NA) analysis demonstrates genetic diversification of the H3N2 CIVs, which evolves independently between Korea and China.

Keywords: Canine influenza virus; H3N2 CIV; Korea; Molecular analysis; Phylogenetic analysis.

Fig. 1

Phylogenetic trees of CIVs according to genotypes based on M (a) and NS (b). Korean isolates are shown in blue; CIVs isolated in the present study are shown in red and the Thailand isolate in green. The remaining isolates are from China. Numbers at nodes indicate support values for maximum likelihood (RAxML) and posterior probabilities for Bayesian inference (MrBayes). Only support values >50 are shown. H3N2 isolates belonging to distinct lineages separated from H3N2 CIVs are in magenta with two asterisks. Genotypes for each group are indicated with vertical lines. Each tree is rooted on the most distant group or isolate, based on p-genetic distance (See Table S2)

Fig. 2

Bayesian inference phylogenetic tree of 40 H3N2 CIVs based on the concatenated eight segments. Korean isolates are shown in blue; CIVs isolated in the present study are in red, and the Thailand isolate is in green. The remaining isolates are from China. Support values from ML analyses are presented with posterior probabilities for Bayesian inference. Only support values >50 are shown. An asterisk at the node indicates high support values presenting more than 98 in ML and 1.0 of BI analyses in all of the analyses

Fig. 3

Median-joining phylogenetic network of H3N2 CIVs based on HA and NA. Each unique sequence is represented by a circle, the size of which is proportional to haplotype frequency. The small lines and black dots reflect mutations and median vectors, respectively. H3N2 CIVs are colored according to geographical locations