Several vaccination approaches have been development to control infectious bursal disease (IBD). Inactivated IBDV-full antigen or subunit vaccines are very safe and may induce high levels of circulating antibodies. They are primarily used for booster vaccination of breeders. For many years, classical attenuated IBDV live vaccines categorized as mild, intermediate and intermediate plus (hot) strains as well as vaccine strains against antigenic variants have been used to vaccinate chickens all over world. But shortcomings are associated with these live vaccine strains. These include residual immunosuppressive effects, interference with maternally derived IBDV-antibodies (MDA) and subsequently poor immune responses. In addition attenuated vaccine strains pose the risk of reversion to virulence as well as of reassortment or recombination with circulating field strains.

Therefore alternative vaccine candidates have been developed. IBDV virus protein 2 (VP2) is an important structural protein, which carries immunodominant epitopes.
Neutralizing antibodies are directed against VP2 and are associated with protection. New generation IBD-vaccines include VP2-based peptide-, DNA- as well as vector-vaccines. Recombinant turkey herpes virus-based vector vaccines expressing IBDV VP2 (rHVT-IBD) have been licensed in many countries. Comparing the rHVT-IBD-vaccine with other commercially available vaccine types it was shown that this vector-based vaccine is safe, and can even in the presence of MDA induce high levels of IBDV-specific antibodies and cell-mediated immunity protecting vaccinated chickens against classical virulent, very virulent IBDV strains as well as antigenic variants. It was shown that rHVT-IBD may spread to different immune tissues including spleen and bursa of Fabricius, the main target organ of IBDV. rHVT-IBD persists providing long term expression of IBDV-VP2 and protection, which gets greater as the time between vaccination and challenge increases. No measurable immunosuppressive effects can be detected after rHVT-IBD-vaccination, which is different to IBD-live and IBDV-immune complex vaccines. Moreover early rHVT-IBD vaccination may even lead to immune enhancement and potentiation of the humoral immune response after vaccination with other poultry vaccines.

Overall, a variety of vaccination strategies is available to protect broilers, layers as well as breeders against IBD in the field, some of which can already be applied early by in ovo or post hatch vaccination at 1 day of life. Circulating field strains need to be monitored to determine the efficacy of the chosen strategy.

Dr. Silke Rautenschlein