Submitted to: Journal of Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/16/2004
Publication Date: 8/1/2004
Citation: Lee, C.W., Senne, D.A., Suarez, D.L. 2004. Effect of vaccine use in the evolution of mexican-lineage h5n2 avian influenza virus. Journal of Virology. Aug. 2004, p 8372-8381. Interpretive Summary: Avian influenza can cause a severe disease in our domestic poultry species, including chickens and turkeys. Vaccination can be an effective way to prevent disease and reduce the amount of virus that is produced in infected birds. For these reasons vaccination is being used more commonly. However, with influenza vaccines for humans, the virus strain must be evaluated yearly, because changes in the virus and the vaccine can result in poor protection, a term known as antigenic drift. This antigenic drift has not been observed in poultry, but vaccination in birds is typically not done for long periods of time. An outbreak of H5 influenza in Mexico provided an opportunity to look at antigenic drift because the virus has remained in Mexico for over eight years and vaccination was used for most of that time. Examination of the commercial vaccine and viruses isolated from Mexico over the eight years showed the same types of changes that were observed in humans. Therefore avian influenza vaccines should also be reconsidered yearly for updates to achieve optimal protection.
Technical Abstract: An outbreak of low pathogenic H5N2 avian influenza (AI) occurred in Mexico in 1993, and the virus mutated to the highly pathogenic form in 1994-95. The highly pathogenic virus was contained, but the low pathogenic virus has remained endemic in Mexican poultry in some states and has spread to two surrounding countries (El Salvador and Guatemala), even though control measures, including vaccination since 1995, have been used. Because this is the first case of long-term use of AI vaccines in poultry, the Mexican-lineage virus presents us with a unique opportunity to examine the evolution of AI virus in the presence of vaccination pressure. We analyzed the coding sequence of HA1 subunit of HA and NS gene of 52 Mexican-lineage viruses that were isolated between the years 1993 and 2002. Phylogenetic analysis indicated the presence of multiple sublineages of Mexican-lineage isolates at the time vaccine was introduced. Further, most of the viruses isolated after the introduction of vaccine belonged to sublineages separate from the vaccine sublineage. Serologic analysis using hemagglutination inhibition and virus neutralization tests showed major antigenic differences among isolates belonging to the different sublineages. In vivo vaccine protection studies further confirmed the in vitro serologic results that commercial vaccine was not able to prevent virus shedding when chickens were challenged with antigenically different isolates. These findings indicate that antigenic drift, which has not been observed in AI virus, is occurring in the Mexican-lineage AI viruses and the persistence of the virus in the field is likely aided by its extreme antigenic difference to the vaccine strain.