title: Impact of antigenic and genetic drift on the serologic surveillance of H5N2 avian influenza viruses.
abstract: BACKGROUND
  Serologic 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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Washington University School of Medicine, Dept. Pathology and Immunology, St. Louis, MO 63110, USA.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Escorcia
authors.forename: Karol
authors.initials: K
authors.lastname: Carrillo-Sánchez
authors.forename: Santiago
authors.initials: S
authors.lastname: March-Mifsut
authors.forename: Joaquin
authors.initials: J
authors.lastname: Chapa
authors.forename: Eduardo
authors.initials: E
authors.lastname: Lucio
authors.forename: Gerardo M
authors.initials: GM
authors.lastname: Nava
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000235:genetics*; D040961:Genetic Drift; D006385:Hemagglutination Inhibition Tests / Q000662:veterinary; D053125:Influenza A Virus, H5N2 Subtype / Q000235:genetics* / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000276:immunology; D005585:Influenza in Birds / Q000453:epidemiology / Q000517:prevention & control / Q000821:virology*; D008800:Mexico / Q000453:epidemiology; D008969:Molecular Sequence Data; D010802:Phylogeny; D011200:Poultry; D016036:Seroepidemiologic Studies; D013997:Time Factors
chemical_list: D000956:Antigens, Viral; D007252:Influenza Vaccines