Emergence of human-like H3N2 influenza viruses in pet dogs in Guangxi, China

Abstract

Background: After the 1968 H3N2 pandemic emerged in humans, H3N2 influenza viruses continuously circulated and evolved in nature. An H3N2 variant was circulating in humans in the 1990s and subsequently introduced into the pig population in the 2000s. This virus gradually became the main subtype of swine influenza virus worldwide. However, there were no reports of infections in dogs with this virus.

Findings: In 2013, 35 nasal swabs from pet dogs were positive for Influenza A virus by RT-PCR. Two viruses were isolated and genetically characterized. In the phylogenetic trees of all gene segments, two H3N2 canine isolates clustered with Moscow/10/99 and most H3N2 swine influenza viruses. These results indicated that two H3N2 CIVs possessed high homology with human/swine influenza viruses, which at the same time exhibited some amino acid substitutions in NA, polymerase basic protein 1 (PB1), and nucleoprotein (NP), which probably were related to the interspecies transmission.

Conclusions: These two viruses share the highest homology with swine H3N2, Moscow/99-like viruses, which indicated that these viruses might originate from swine viruses.

Figure 1

Phylogenetic trees of eight gene segments of two H3N2 CIVs and reference isolates. The trees were generated with the MEGA 5.2 program using neighbor-joining analysis. The bootstrap percentages are shown above the nodes that were supported in >70% of 1000 replicates. The viruses isolated in our study are shown in black round circles. The phylogenetic trees are shown in (a) HA gene, (b) NA gene, (c) NP gene, (d) PA gene, (e) PB1gene, (f) PB2 gene, (g) M gene, and (h) NS gene.

Figure 2

Alignment of HA1 amino acid sequences of two H3N2 CIVs and representative H3N2 human and swine influenza viruses. Antigenic sites are indicated by solid boxes (lower case letters indicate discrete antigenic sites), residues in yellow denote the receptor-binding sites, and residues in grey represent the potential glycosylation sites. The cleavage sites are in the dotted box.