Genetic characterization of H1N2 influenza a virus isolated from sick pigs in Southern China in 2010

Influenza viruses are members of family Orthomyxoviridae and have segmented, Negative-sense RNA genomes. Swine influenza virus (SIV) belongs to Influenza A Viruses. SIV causes respiratory diseases in pigs and has been disseminated all over the world [1]. At present, there were three main influenza viruses circulating in pigs in the world including H1N1, H1N2 and H3N2. In addition some other unusual subtypes of swine influenza were also reported includingH1N7, H3N1, H4N6, H5N1, H5N2, H6N6 and H9N2 [2-7].The first SIV H1N2 was reported in Japan from 1978 to 1992 [8,9]. From then on, H1N2 was show up in different pigs of different countries, including France from 1987 to 1988 [10], and in the United Kingdom in 1994 [11], the United States in 1999 [12], Germany in 2000 [13], Korea in 2003 and thereafter [14]. Recently it first shows up in Swedish herd [15]. During an influenza virus surveillance programme in Guangdong pigs, we isolated an H1N2 virus from clinically ill pigs, which was genetically characterized as a result of reassortment events between a human H3N2 strain, Classical SIV strain and North America avian-like SIV lineage strain.In January of 2010, some pigs have a severe outbreak of influenza-like disease occurred in an intensive pig farm of Guangdong province. Many pigs have similar clinical symptoms: cough, sneeze, runny nose. These clinical symptoms last for 3-8 days then some pigs have sick of foot and mouth disease (FMD). Because Swine influenza (SI) was immunosuppressive disease which frequently predisposesed to highly fatal secondary infections. Maybe the SI lowers pig's immunity to common illnesses, some pigs will get FMD. From now on, the FMD caused rampant epidemic diseases in pig population of Guangdong [16].Initial isolations of the viruses were performed in 10-day-old specific pathogen free (SPF) embryonated chicken eggs through the allantoic route, incubated at 35°C for 72 h. Embryonic death was monitored every 12 h, and then allantoic fluid w