Genetic correlation between H3N2 human and swine influenza viruses.

BACKGROUND H3N2 is one of the main subtypes of influenza virus which circulates in human and swine population throughout the world. OBJECTIVES To investigate the genetic correlation between H3N2 human and swine influenza viruses from the same region during the same season. STUDY DESIGN Five H3N2 human and four H3N2 swine influenza viruses were isolated from Guangdong province of China in the winter of 2005. The molecular evolution of eight gene segments was analyzed. RESULTS In the phylogenetic trees of gene segments, all H3N2 human isolates along with the 2000's human isolates formed a cluster, and most of the H3N2 swine isolates along with the 1990's human isolates formed another cluster except that the M and NS gene of A/Swine/Guangdong/01/2005 and the PA gene of A/Swine/Guangdong/02/2005 fell into the cluster of the classical swine influenza virus, indicating the reassortment between H3N2 human and H1N1 swine influenza viruses. CONCLUSIONS In this study, H3N2 swine influenza viruses in 2005 did not originate from the 2000's H3N2 human influenza viruses, but from the 1990's H3N2 human isolates. In addition, the reassortment of H3N2 human and H1N1 swine influenza virus in pigs was common in recent years.