Temporal insight into the natural generation of a new reassortant porcine influenza virus in a swine holding

•We performed passive IAV viral surveillance in a pig farm between 2012 and 2013.•We isolated 10 IAVs from episodes of respiratory disease in 45-70 day-old pigs.•All these viruses were sequenced and we performed the antigenic characterization.•We showed the circulation of H1N1pdm, H1N1 avian-like and pdmH1avN1 reassortant IAV.•The reassortant H1N1 evolved from the pandemic H1N1 strain and an avian-like H1N1.

The influenza A virus (IAV) subtypes H1N1, H3N2 and H1N2 are the most prevalent subtypes in swine in Italy. Reassortant influenza A viruses subtypes in swine appeared in European pig population. In particular reassortant viruses carrying genome segment from the pandemic H1N1 (H1N1pdm) are reported in many European countries, including Italy. In a 1000 sows farrow-to feeder farm, in Northern Italy, we isolated 10 IAVs from recurrent episodes of respiratory disease in 45-70 days-old pigs from September 2012 to June 2013. The antigenic and genetic characterization of the swine IAV isolates showed the contemporary circulation of H1N1 avian-like and H1N1pdm strains in the first outbreak. The analysis of the viruses isolated subsequently showed the circulation of H1N1pdm IAV and then the establishment of a new previously undescribed H1N1 reassortant strain with a pandemic derived hemagglutinin gene and all the other seven segments of swine H1N1 avian-like lineage.