Short report

Avian influenza: genetic evolution under vaccination pressure

Magdalena Escorcia¹ , Lourdes Vázquez¹ , Sara T Méndez² , Andrea Rodríguez-Ropón³ , Eduardo Lucio³ and Gerardo M Nava^1,4

¹  Departamento de Producción Animal Aves. Facultad de Medicina Veterinaria y Zootecnia. Universidad Nacional Autónoma de México, D. F. 04510, México

²  Unidad de Genética de la Nutrición. Instituto Nacional de Pediatría, D. F, 04530, México

³  Investigación Aplicada, S. A. de C. V. 7 Norte 416, Tehuacán, Puebla, 75700, México

⁴  Laboratory of Mucosal Biology. University of Illinois at Urbana-Champaign, 61801, USA

author email corresponding author email

Virology Journal 2008, 5:15doi:10.1186/1743-422X-5-15

Published:	24 January 2008

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.