USE OF RECOMBINANT TECHNOLOGY IN THE DEVELOPMENT OF POULTRY VACCINES

The use of vaccines against infectious diseases has been one of the true success stories of modern medicine. Vaccines are the most effective and inexpensive prophylactic tools in veterinary medicine. Traditionally, there are two major categories of classical vaccines: one employing modified live attenuated organism and the other employing chemically inactivated organism. Vaccines produced by conventional technologies are imperfect in many respects with regard to safety, efficacy and cost. The unsatisfactory efficacy, safety, antigenic variation and the emergence of new diseases dictate the need to develop newer and more effective vaccines. For many years considerable scientific effort has been directed towards the development of novel vaccine technologies, aiming at improving the efficacy and safety of vaccines. The current knowledge in viral DNA and RNA vectors as carriers of foreign antigens, illustrates many of the potential approaches for development of veterinary vaccines. Increasing demand in the design ofveterinary vaccines is the ability to distinguish between infected and vaccinated animals (DIVA). This is particularly important in eradication campaigns. Other considerations for an ideal vaccine: (i) to be multivalent and induces specific immunity against the protective antigens; (ii) protects against both the disease and infection; (iii) protects young animals regardless of passively acquired antibodies; (iv) elicits long duration of immunity without requiring booster doses; (v) to be free of adverse reactions; (vi) could easily be administered by mass vaccination; and (vii) lacks the potential for environmental spread including in non-target species. Using recombinant DNA (rDNA) technologies, scientists have been able to develop three types of recombinant vaccines: (i) live genetically modified organisms, (ii) recombinant inactivated subunit vaccines, and DNA vaccines. By introducing multiple gene deletions in the genome of pathogen organism, it is possible to generate new class of attenuated vaccines that are safe and may not result in reversion to virulence. Recombinant DNA technology has also made it possible to generate vaccines utilizing viruses as vectors for the expression of protective antigens of other organism. This new class of vaccine is called vectored vaccine Interestingly, the first vaccine ever used became one of the most widely used systems for foreign antigen delivery, the poxvirus vectors. Since then, many other DNA viruses, including herpesviruses, adenoviruses and baculoviruses have been used in the development of vaccines. More recently, the refinement of reverse genetics technologies allowed the use of RNA viruses as potential expression or delivery vectors.This paper provides brief overview of the basic categories of recombinant vaccines and describes these technologies which have already led to the development of some important veterinary poultry vaccines.