Molecular epidemiology of porcine H3N2 influenza A viruses isolated in Germany between 1982 and 2001.

We examined influenza virus strains of the subtype H3N2 from outbreaks of respiratory diseases in swine herds in Germany. Four different clusters can be distinguished when comparing parts of the HA1 gene from porcine H3N2 isolates analyzed between 1982 and 2001. Comparison between these clusters reveals a bp homology of less than 90%. In contrast, the homology within the clusters is between 93.7 and 100%. Each of these clusters was confined to a specific time period. For the NA gene an additional cluster is formed by the porcine H1N2 isolate. The findings that different subtypes and drift variants are circulating in the German pig population explain the emergence of new influenza virus variants and the need for continued surveillance of swine.