Developments in Avian Influenza Virus Vaccines

Abstract

The serologically diverse influenza A viruses, although transmissible among various susceptible species, mostly infect avian species. Avian influenza viruses (AIV) are also notorious for adapting to mammalian species, including humans. Although eradication of commercial birds infected with AIV is the preferred method of control, the ever presence of potential avian migratory, reservoir species makes worldwide spread inevitable and vaccine development a high priority for poultry. Live, attenuated vaccine strategies are of concern because of the potential of AIV to mutate, through point mutations and/or reassortment of their segmented genome. Both live and the safer, killed vaccines are of concern because of competition of natural and vaccine antigens in critical diagnostic assays. Subunit vaccines, which allow for protein distinction for diagnostic purposes, may consist of purified AIV protein or genes that encode individual viral proteins. Most vaccines have targeted the virus hemagglutinin protein, which is responsible for induction of the most effective neutralizing antibodies. Gene vaccines that include plasmid DNA and viral vector delivery of AIV genes allow for endogenous in vivo amplification of protein within cells. While fowlpox virus vectors have been licensed and proven to be efficacious even in field situations, other viral vectors that target the respiratory tract are in experimental development with promising practical application for poultry. Maximum exploitation of vectored vaccines may incorporate enhancing immune molecules.