title: Avian influenza: genetic evolution under vaccination pressure.
abstract: Antigenic drift of avian influenza viruses (AIVs) has been observed in chickens after extended vaccination program, similar to those observed with human influenza viruses. To evaluate the evolutionary properties of endemic AIV under high vaccination pressure (around 2 billion doses used in the last 12 years), we performed a pilot phylogenic analysis of the hemagglutinin (HA) gene of AIVs isolated from 1994 to 2006. This study demonstrates that Mexican low pathogenicity (LP) H5N2-AIVs are constantly undergoing genetic drifts. Recent AIV isolates (2002-2006) show significant molecular drifts when compared with the H5N2 vaccine-strain or other field isolates (1994-2000). This study also demonstrates that molecular drifts in the HA gene lineages follow a yearly trend, suggesting gradually cumulative sequence mutations. These findings might explain the increasing incidence of LP H5N2 AIV isolated from commercial avian farms. These findings support recent concerns about the challenge of AIV antigenic drift and influenza epidemics.
authors.affiliation: Departamento de Producción Animal Aves, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México, DF 04510, México. magdaescorcia@exalumno.unam.mx
authors.forename: Magdalena
authors.initials: M
authors.lastname: Escorcia
authors.forename: Lourdes
authors.initials: L
authors.lastname: Vázquez
authors.forename: Sara T
authors.initials: ST
authors.lastname: Méndez
authors.forename: Andrea
authors.initials: A
authors.lastname: Rodríguez-Ropón
authors.forename: Eduardo
authors.initials: E
authors.lastname: Lucio
authors.forename: Gerardo M
authors.initials: GM
authors.lastname: Nava
mesh_terms: D000818:Animals; D002645:Chickens; D019353:Endemic Diseases / Q000662:veterinary*; D019143:Evolution, Molecular; D040961:Genetic Drift; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics; D053125:Influenza A Virus, H5N2 Subtype / Q000145:classification / Q000235:genetics / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000276:immunology*; D005585:Influenza in Birds / Q000453:epidemiology / Q000276:immunology* / Q000821:virology*; D008800:Mexico / Q000453:epidemiology; D010802:Phylogeny; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007252:Influenza Vaccines; C109963:hemagglutinin, avian influenza A virus