Impact of antigenic and genetic drift on the serologic surveillance of H5N2 avian influenza viruses

Phylogenetic analysis revealed significant divergence between early LPAI H5N2 viruses (1994 - 1998) and more recent virus field isolates (2002 - 2008). Results of the HI test were markedly influenced by the selection of the AI H5N2 virus (year of isolation) used as reference antigen for the assay. These analyses indicate that LPAI H5N2 viruses in Mexico are constantly undergoing genetic drift and that serosurveillance of AI viruses is significantly influenced by the antigen or antisera used for the HI test.Reference viral antigens and/or antisera need to be replaced constantly during surveillance of AI viruses to keep pace with the AI antigenic drift. This strategy should improve the estimation of antigenic differences between circulating AI viruses and the selection of suitable vaccine strains.Avian Influenza (AI) virus belongs to the Orthomyxoviridae family, Influenzavirus A genus. This virus possesses eight segments of single-stranded RNA genome. Two of these segments encode for two important membrane glycoproteins, hemagglutinin (HA) and neuraminidase (NA) [1], that play a key role during cellular infection. These two proteins are used for virus subtype classification [1,2]. Also, depending on severity of disease in avian species, AI viruses are categorized into highly- and low-pathogenic (HPAI and LPAI, respectively) viruses [1,2].In response to the recent cases of human infections caused by HPAI H5N1 viruses, authorities and scientists were encouraged to review and apply policies for effective surveillance and control of AI infections [3-5]. In many countries, the use of AI vaccines was banned or discouraged because vaccination programs could interfere with appropriate detection of HPAI outbreaks [5]. However, the use of AI vaccines has been reconsidered by some countries due to the recent increase in AI cases in commercial farms and devastating consequences for human health [5].In Mexico, an AI vaccination program was established in 1994. Initially, the progr