Cocirculation of Avian H9N2 and Contemporary “Human” H3N2 Influenza A Viruses in Pigs in Southeastern China: Potential for Genetic Reassortment?

Abstract

Pigs are permissive to both human and avian influenza viruses and have been proposed to be an intermediate host for the genesis of pandemic influenza viruses through reassortment or adaptation of avian viruses. Prospective virological surveillance carried out between March 1998 and June 2000 in Hong Kong, Special Administrative Region, People's Republic of China, on pigs imported from southeastern China, provides the first evidence of interspecies transmission of avian H9N2 viruses to pigs and documents their cocirculation with contemporary human H3N2 (A/Sydney/5/97-like, Sydney97-like) viruses. All gene segments of the porcine H9N2 viruses were closely related to viruses similar to chicken/Beijing/1/94 (H9N2), duck/Hong Kong/Y280/97 (H9N2), and the descendants of the latter virus lineage. Phylogenetic analysis suggested that repeated interspecies transmission events had occurred from the avian host to pigs. The Sydney97-like (H3N2) viruses isolated from pigs were related closely to contemporary human H3N2 viruses in all gene segments and had not undergone genetic reassortment. Cocirculation of avian H9N2 and human H3N2 viruses in pigs provides an opportunity for genetic reassortment leading to the emergence of viruses with pandemic potential.

Inferring patterns of influenza transmission in swine from multiple streams of surveillance data

“…While the pandemic did not arise in China, the co-circulation of multiple lineages and genetic reassortment events observed in the course of this surveillance provide insight into likely virus transmission dynamics leading up to pandemic emergence in the Americas [5,6]. The joint analysis of virological and serological data allows us to infer time-varying risks of influenza exposure across production stages, despite the fact that samples were taken at a single location.…”

“…One conspicuous exception is a dataset describing long-term virological and serological surveillance at a Hong Kong abattoir from 1998 to 2010, drawn from source farms across southern and southeastern China. These data have already yielded important insights about the co-circulation of influenza strains, strain replacement and viral reassortment in swine populations [5,6]. However, fundamental questions have yet to be addressed.…”

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“…This clade contains Chinese sequences that were isolated from chickens between 1999-2002. This topology agrees with those from the existing literature except that there is some disagreement in the identification of the lineages (Li et al 2003;Peiris et al 2001;Perk et al 2006;Yu et al 2008). Ji used a lineage and sub-lineage nomenclature that identified four lineages and 2 sub-lineages corresponding to Clade A (lineages 9.1, 9.2 and 9.3), Clade B (sub-lineage 9.4.1) and the main Chinese Clade (sub-lineage 9.4.2).…”

Epidemiological update on swine influenza (H1N1) in pigs

“…It is noteworthy that, until now, there has been no evidence of Eurasian avian-like swine H1N1 circulating in North American pigs. In Asia, the classical swine infl uenza lineage circulates, in addition to other identifi ed viruses, including human H3N2, Eurasian avian-like H1N1, and North American triple reassortant H3N2 [47][48][49].…”

“…The respiratory tract epithelial cells in pigs contain the sialic acid receptors preferred by both avian (α 2, 3-N-acetylneuraminic acid-galactose) and human infl uenza viruses [47,62]. Pigs can therefore function as intermediate hosts or "mixing vessels" in establishing new infl uenza virus lineages by supporting co-infection, replication, and re-assortment among human, avian and swine infl uenza viruses [27,63].…”