Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2009
Publication Date: 10/1/2009
Citation: Vincent, A.L., Ma, W., Lager, K.M., Gramer, M.R., Richt, J.A., Janke, B.H. 2009. Characterization of a Newly Emerged Genetic Cluster of H1N1 and H1N2 Swine Influenza Virus in the U.S. Virus Genes. 39(2):176-185. Interpretive Summary: Swine influenza virus (SIV) is one of the primary causes of respiratory disease in growing pigs and can lead to major economic losses to the swine industry. In addition to SIV, pigs can become infected with influenza viruses from birds and humans and produce viruses with a mixture of genetic material. A new type of SIV has emerged in the United States that contains genetic material from H1 human influenza viruses as well as genetic material from contemporary SIV. In this paper, we examine the full genetic makeup of 4 of the recently emerged human-like H1 SIV and the properties of one of these viruses in a pig infection study. Closer monitoring of pig and human populations for this and other SIV is warranted.
Technical Abstract: H1 influenza A viruses that were distinct from the classical swine H1 lineage were identified in pigs in Canada in 2003-2004; antigenic and genetic characterization identified the hemagglutinin (HA) as human H1 lineage. The viruses identified in Canadian pigs were human lineage in entirety or double (human-swine) reassortants. Here we report the whole genome sequence analysis of 4 human-like H1 viruses isolated from U.S. swine in 2005 and 2007. All 4 isolates were characterized as triple reassortants with an internal gene constellation similar to contemporary U.S. swine influenza virus (SIV), with HA and neuraminidase (NA) most similar to human influenza virus lineages. A 2007 human-like H1N1 was evaluated in a pathogenesis and transmission model and compared to a 2004 reassortant H1N1 SIV isolate with swine lineage HA and NA. The 2007 isolate induced disease typical of influenza virus and was transmitted to contact pigs; however the kinetics and magnitude differed from the 2004 H1N1 SIV. This study indicates that the human-like H1 SIV can efficiently replicate and transmit in the swine host and now co-circulates with contemporary SIVs as a distinct genetic cluster of H1 SIV.