Abstract
Prior to the emergence of H3N8 canine influenza virus (CIV) and the latest avian-origin H3N2 CIV, there was no evidence of a circulating canine-specific influenza virus. Molecular and epidemiological evidence suggest that H3N8 CIV emerged from H3N8 equine influenza virus (EIV). This host-range shift of EIV from equine to canine hosts and its subsequent establishment as an enzootic CIV is unique because this host-range shift was from one mammalian host to another. To further understand this host-range shift, we conducted a comprehensive phylodynamic analysis using all the available whole-genome sequences of H3N8 CIV. We found that (1) the emergence of H3N8 CIV from H3N8 EIV occurred in approximately 2002; (2) this interspecies transmission was by a reassortant virus of the circulating Florida-1 clade H3N8 EIV; (3) once in the canine species, H3N8 CIV spread efficiently and remained an enzootic virus; (4) H3N8 CIV evolved and diverged into multiple clades or sublineages, with intra and inter-lineage reassortment. Our results provide a framework to understand the molecular basis of host-range shifts of influenza viruses and that dogs are potential “mixing vessels” for the establishment of novel influenza viruses.
Highlights
Influenza A virus (IAV) is a member of Orthomyxoviridae
Origin of H3N8 canine influenza virus (CIV) In agreement with published reports, both temporal-spatial and molecular evidence suggest that H3N8 CIV originated from H3N8 equine influenza virus (EIV)
According to the topology of this concatenated maximum likelihood (ML) tree, H3N8 CIV could be divided into six major clades
Summary
Influenza A virus (IAV) is a member of Orthomyxoviridae. According to the antigenicity of the two viral surface proteins, haemagglutinin (HA) and neuraminidase (NA), IAV is currently classified into 17 HA and 9 NA subtypes. All combinations of the 17 HA and 9 NA subtypes have been found in waterfowl, its natural host [1]. Only a few defined combinations of HA and NA subtypes circulate in mammalian hosts, e.g., H3N2 and H1N1 among humans and pigs and H3N8 among horses. The establishment of these mammalian influenza viruses, including human influenza A virus (hIAV), was the result of interspecies transmission of an
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