Genetic characterization of swine influenza viruses isolated in Japan between 2009 and 2012.

Eleven swine influenza viruses (SIVs) isolated from pigs in Japanese institutions between 2009 and 2012 were genetically characterized. Seven H1N1 were shown to have originated from A(H1N1)pdm09 viruses. Two H1N2 viruses contained H1 and N2 genes of Japanese H1N2 SIV origin together with internal genes of A(H1N1)pdm09 viruses. Two H3N2 viruses isolated during animal quarantine were identified as triple reassortant H3N2 viruses maintained among pigs in North America. This study shows that A(H1N1)pdm09 viruses and their reassortant strains are already present in domestic pigs in Japan and that novel SIVs are possibly being imported from abroad.