Submitted to: Swine Disease Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/21/2013
Publication Date: 11/14/2013
Citation: Kehrli Jr, M.E., Vincent, A.L., Loving, C.L., Lager, K.M. 2013. Swine influenza virus vaccine research and technology: What does the future hold and what are our next steps? Swine Disease Conference Proceedings, November 14-15, 2013, Ames, Iowa. p. 16-20.
Technical Abstract: Swine influenza represents a problem for the health of pigs and the economic health of the swine industry due to real and perceived public health risks. This is largely driven by the diversity of influenza A viruses (IAV) in swine herds. Antigenic drift (mutations) and shifts (reassortments) by influenza viruses are continually occurring. The RNA polymerase error rate among IAV is ~2 X 10-3 nucleotide substitutions/site/year1 and whenever a single cell is infected by 2 different influenza viruses, reassortment events between the viruses can occur and result in as many as 256 different gene combinations. These 2 types of genetic change provide the basis of the marked genetic and antigenic diversity in contemporary IAV in North American swine. In addition, interspecies transmission is an important contributor to the genetic diversity of IAV found in swine. For example, at least 23 separate human-to-swine transmission events of human seasonal H1 and H3 influenza viruses have been identified globally since 1990. The global ecology of influenza A viruses (IAV) in swine can be separated by geographic regions, with North American lineages genetically distinct from European swine lineages. In North America, the classical swine H1N1 virus was dominant until the seasonal human H3N2 virus was introduced into pigs in 1998 and followed by at least two additional, separate introductions of human H1 viruses. At present, seven major antigenically distinct hemagglutinin (HA) lineages, H1a, H1ß, H1', H1d1, H1d2, H1N1pdm09 and H3 cluster IV (c4) co-circulate in North American swine populations. Until 2009, all dominant HA lineages except for the H1N1pdm09 virus contained the ‘triple reassorted internal gene’ (TRIG) constellation of swine (M, NP and NS genes), avian (PB2 and PA genes), and human (PB1) lineages identified in swine in 1998. The internal gene constellation in H1N1pdm09 is distinct from the H3N2-TRIG as the M gene is of Eurasian swine lineage and the other 5 genes can be differentiated in a phylogenetic analysis. Within two years after the emergence of H1N1pdm09 in humans, at least 49 influenza spillover events from humans-to-swine were detected globally. The introduction of H1N1pdm09 into pigs subsequently led to multiple reassortment events between H1N1pdm09 and the endemically circulating IAV of swine, greatly increasing the genetic diversity of IAV in swine.