Abstract

BackgroundSerologic surveillance of Avian Influenza (AI) viruses is carried out by the hemagglutination inhibition (HI) test using reference reagents. This method is recommended by animal health organizations as a standard test to detect antigenic differences (subtypes) between circulating influenza virus, vaccine- and/or reference- strains. However, significant discrepancies between reference antisera and field isolates have been observed during serosurveillance of influenza A viruses in pig and poultry farms. The objective of this study was to examine the effects of influenza virus genetic and antigenic drift on serologic testing using standard HI assays and reference reagents. Low pathogenic AI H5N2 viruses isolated in Mexico between 1994 and 2008 were used for phylogenetic analysis of AI hemagglutinin genes and for serologic testing using antisera produced with year-specific AI virus isolates.ResultsPhylogenetic 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.ConclusionsReference 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.

Highlights

  • Serologic surveillance of Avian Influenza (AI) viruses is carried out by the hemagglutination inhibition (HI) test using reference reagents

  • Low pathogenic AI H5N2 viruses isolated in Mexico between 2002 and 2008 were used for phylogenetic analyses of AI hemagglutinin genes and immune reactivity using antisera produced with AI virus isolated in different years

  • Virus were replicated in chicken embryo and reverse transcriptase PCR was used for the amplification of the HA gene, a marker for the virulence potential of AI viruses [15]

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Summary

Introduction

Serologic surveillance of Avian Influenza (AI) viruses is carried out by the hemagglutination inhibition (HI) test using reference reagents. 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]. Depending on severity of disease in avian species, AI viruses are categorized into highly- and lowpathogenic (HPAI and LPAI, respectively) viruses [1,2].

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