Genetic drift of HA and NA in Danish swine influenza virus from the period 2003-2012

The aim of this study is to analyze; the genetic drift in hemagglutinin (HA) and neuraminidase (NA) genes from influenza viruses isolated from Danish swine over the past decade; the antigenic evolution and relatedness between swine influenza virus strains of the H1 subtype by antigenic cartography. Currently at least three influenza A subtypes (H1N1, H1N2 and H3N2) are endemic in the Danish swine population, and since 2010 the pandemic virus (H1N1pdm09) have also frequently been detected.

The focus in this study will be on H1N1 and H1N2, since the prevalence of H3N2 have declined over the past years. Obtained isolates derived from diagnostic samples submitted to the Danish National Veterinary Institute for influenza A virus detection. Approximately eight isolates from each of the years 2003 to 2012 are examined by HA and NA full length sequencing and phylogenetic analyses.

In addition, HI-titers obtained by testing against a panel of reference swine influenza virus antisera are used for antigenic cartography. Preliminary phylogenetic analyses indicate a higher degree of drift for H1 genes than N1 genes. The antigenic and genetic characterization of the swine influenza virus isolates in this study will provide a more complete picture of the molecular epidemiology of the H1N1 and H1N2 swine influenza viruses in Denmark.

A thorough knowledge of the antigenic drift in surface genes is very important concerning evaluation of the zoonotic potential of existing and future swine influenza virus strains and along with the monitoring of antigenic changes in hemagglutinin subtypes it will be possible to ensure a continuous efficacy of influenza virus vaccines.