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Evolving vaccine choices for the continuously evolving avian influenza viruses.

By: Drechsler, Y.; Singh, S.; Collisson, E. W.;

2010 / CABI

Description

Avian influenza viruses (AIVs) are a continuously evolving group of RNA viruses with segmented genomes. Although AIV is thought to originate from wild bird populations, the capacity for ready mutation and adaptation to mammalian hosts makes AIV both a potential agricultural and public health risk. Worldwide spread of AIV is inevitable because of the ever-presence of infection in wild, especially migratory, bird reservoirs. Therefore, vaccine development is of high priority. The potential for genetic shift (reassortment) and drift (point mutations) is a concern for dependency on live, attenuated vaccine strategies, which were the first vaccines of wide use in poultry. Inactivated whole virus and subunit protein vaccines provide limited immune responses. The evolution of vaccine strategies is the result of creative applications of genetic engineering to develop plasmid and viral gene delivery vectors. Gene vaccines that include plasmid DNA and viral vector delivery of AIV genes allow for endogenous, in vivo amplification of proteins within cells. The viral vectors are Nature's specialists for cellular delivery of genetic information and, if replication-competent, also for the spread from host cell to cell, furthering opportunities for induction of immunity. Viral proteins that induce neutralizing antibodies are preferred to subunit vaccines. The replication-competent fowlpox virus vectors have been licensed and proved to be efficacious even in field situations. Several avian respiratory viruses, with DNA or RNA genomes, are being developed with promising practical application for poultry. Maximum exploitation of vectored vaccines may incorporate enhancing immune molecules. Future vaccines must also allow for differentiation of vaccinated birds from naturally infected birds.