Comparison of infectious bursal disease live vaccines and a HVT-IBD vector vaccine and their effects on the immune system of commercial layer pullets

Infectious bursal disease (IBD) is an economically important disease affecting poultry production worldwide. Previous experimental studies indicated that IBD live vaccination may induce transient immunosuppression, leading to suboptimal vaccine responses and therefore insufficient protection against other pathogens. Layer pullets are commonly not only vaccinated against IBD within their rearing period, but also against a variety of other pathogens. Therefore, it is of interest to investigate the effects of different IBD vaccination regimes on conventionally applied vaccines against other pathogens, and possible protection against widely spread very virulent IBD-virus (vvIBDV). A commercially available Herpesvirus of turkey vector vaccine (vHVT-IBD) expressing viral protein 2 of IBDV, and two IBD live vaccines were compared in commercial pullets for their effects on circulating B cell numbers, the ability of vaccinated birds to mount a humoral immune response against different antigens as well as their ability to induce protection against vvIBDV challenge. The results of this study demonstrate a clear immunosuppressive effect of the intermediate plus IBD live vaccine on the humoral branch of the immune system. On the other hand, no detectable effects of vHVT-IBD vaccination on these parameters were observed. All tested IBD vaccines protected against clinical IBD, although none induced sterile immunity in commercial layer pullets. vHVT-IBD-vaccinated birds showed significantly less lesions after vvIBDV challenge than IBD live-vaccinated or non-vaccinated birds (P < 0.05). Therefore, vHVT-IBD may be a suitable alternative to conventional IBD live vaccines, and may be applied even in the presence of maternally derived IBD antibodies without induction of detectable humoral immunosuppression.