The emergence of novel influenza viruses among pigs in North America due to interspecies transmission and reassortment

Abstract In 1997–1998, H3N2 influenza viruses of different genotypes emerged among North American pigs. Triple reassortant H3N2 viruses containing human, classical swine and avian virus genes spread widely within the swine population and gave rise subsequently to reassortant H1N2 and H1N1 viruses. Together with wholly avian viruses recovered from North American pigs since 1999, these viruses emphasize that influenza virus interspecies transmission and reassortment in pigs can occur throughout world. They provide important research tools with which the genetic factors that control interspecies transmission can be investigated.