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United States Department of Agriculture

Agricultural Research Service

Research Project: SWINE VIRAL DISEASES PATHOGENESIS AND IMMUNOLOGY Title: Characterization of H1N1 swine influenza viruses circulating in Canadian pigs in 2009

Authors
item Nfon, Charles -
item Berhane, Yohannes -
item Hisanaga, Tamiko -
item Zhang, Shunzhen -
item Handel, Katherine -
item Kehler, Helen -
item Labrecque, Olivia -
item Lewis, Nicola -
item VINCENT, AMY
item Copps, John -
item Alexandersen, Soren -
item Pasick, John -

Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 8, 2011
Publication Date: September 1, 2011
Citation: Nfon, C.K., Berhane, Y., Hisanaga, T., Zhang, S., Handel, K., Kehler, H., Labrecque, O., Lewis, N.S., Vincent, A.L., Copps, J., Alexandersen, S., Pasick, J. 2011. Characterization of H1N1 swine influenza viruses circulating in Canadian pigs in 2009. Journal of Virology. 85(17):8667-8679.

Interpretive Summary: The 2009 pandemic H1N1 (pH1N1) influenza A virus, of apparent swine origin, may have evolved undetected in pigs because of insufficient surveillance. In an effort to increase surveillance for influenza viruses in Canadian swine, we characterized H1N1 viruses isolated in 2009 before and after the emergence of the pandemic. Swine virus isolates from May 2009 prior to the pH1N1 outbreaks in humans and pigs in Canada contained HA and NA genes of classical swine influenza virus (SIV) origin in combination with the North American triple reassortant internal gene (TRIG) cassette hereby termed contemporary SIV H1N1. These contemporary SIV H1N1 viruses were related to the North American alphaH1 cluster SIV and were distinct from the pH1N1 isolates. The pH1N1 viruses were more related to the gammaH1 cluster SIV, although the pH1N1 isolates were distinct from Canadian contemporary SIV. Following the initial isolation of pH1N1 from an Alberta pig farm in early May 2009, pH1N1 was found several times in Canadian pigs. These pH1N1 isolates were highly similar to each other and to human isolates. In addition to alphaH1 cluster and pH1N1 viruses, H1N1 viruses bearing seasonal human H1 and N1 genes together with the TRIG cassette and a NA encoding an oseltamivir-resistance marker were isolated from pigs. The NS gene of one of these seasonal human-like SIV (shSIV) H1N1 isolates was highly similar to pH1N1 NS gene, implicating mixing of the genetic material between the two strains. Cross-reactivity in serum antibody assays was observed between pH1N1 and contemporary SIV but not with shSIV H1N1. In summary, although there was co-circulation of pH1N1 with contemporary SIV and shSIV H1N1 in Canadian pigs after May 2009, there was no evidence supporting the presence of pH1N1 in pigs prior to May 2009. The possibility for further genetic mixing between pH1N1 and contemporary SIV exists and generation of viruses with new combinations of genes should be closely monitored by sustained surveillance in the swine population.

Technical Abstract: The 2009 pandemic H1N1 (pH1N1), of apparent swine origin, may have evolved in pigs unnoticed because of insufficient surveillance. Consequently, the need for surveillance of influenza viruses circulating in pigs has received added attention. In this study we characterized H1N1 viruses isolated from Canadian pigs in 2009. Isolates from May 2009 were comprised of HA and NA genes of classical SIV origin in combination with the North American triple reassortant internal gene (TRIG) cassette hereby termed contemporary SIV (conSIV) H1N1. These conSIV H1N1 viruses were contiguous with the North American alphaH1 cluster which was distinct from the pH1N1 isolates which were antigenically more related to the gammaH1 cluster. Following the initial isolation of pH1N1 from an Alberta pig farm in early May 2009, pH1N1 was found several times in Canadian pigs. These pH1N1 isolates were genetically and antigenically homogenous. In addition, H1N1 viruses bearing seasonal human H1 and N1 genes together with the TRIG cassette and a NA encoding an oseltamivir-resistance marker were isolated from pigs. The NS gene of one of these seasonal human-like SIV (shSIV) H1N1 isolates was homologous to pH1N1 NS implicating reassortment between the two strains. Antigenic cross-reactivity was observed between pH1N1 and conSIV but not with shSIV H1N1. In summary, although there was co-circulation of pH1N1 with conSIV and shSIV H1N1 in Canadian pigs after May 2009, there was no evidence supporting the presence of pH1N1 in pigs prior to May 2009. The possibility for further reassortants being generated exists and should be closely monitored.

Last Modified: 7/28/2014
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