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J Gen Virol. 2013 Jun;94(Pt 6):1236-41. doi: 10.1099/vir.0.51839-0.

Genotype patterns of contemporary reassorted H3N2 virus in US swine.

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Virus and Prion Disease Research Unit, National Animal Disease Center, USDA-ARS, Ames, IA 50010, USA.


To understand the evolution of swine-origin H3N2v influenza viruses that have infected 320 humans in the USA since August 2011, we performed a phylogenetic analysis at a whole genome scale of North American swine influenza viruses (n = 200). All viral isolates evolved from the prototypical North American H3 cluster 4 (c4), with evidence for further diversification into subclusters. At least ten distinct reassorted H3N2/pandemic H1N1 (rH3N2p) genotypes were identified in swine. Genotype 1 (G1) was most frequently detected in swine and all human H3N2v viruses clustered within a single G1 clade. These data suggest that the genetic requirements for transmission to humans may be restricted to a specific subset of swine viruses. Mutations at putative antigenic sites as well as reduced serological cross-reactivity among the H3 subclusters suggest antigenic drift of these contemporary viruses.

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