Efficacy of recombinant HVT + IBD + H5 vaccine against novel variant infectious bursal disease, A2dB1b, in broiler and SPF chickens

The increasing prevalence of antigenic variations and genetic reassortments of Infectious Bursal Disease virus (IBDV) across various global regions, causing subclinical infections, poses a significant threat to the poultry industry, leading to substantial losses. In the current study, the protective efficacy of recombinant trivalent vaccine rHVT + IBD + H5, administered once at 1-day old (DO) in the hatchery was assessed against challenge with the most recent circulating novel variant IBD (nVarIBDV), A2dB1b, Egyptian isolate (IBD/EGY/F1335/2023) in commercial broiler, and specific pathogen free (SPF) chickens at 28 DO. A total of 210, commercial broilers and 120 SPF chicks, housed at BSL-3 conditions, were divided into 11 equal groups (Broilers, G1-G7, and SPF G8-G11, n = 30/group). The bursa/body weight ratio (BBR) and bursa/body weight index (BBI) scores calculated at 4-, 7-, 10-, and 14-days post-infection (DPC) revealed significantly higher scores in the vaccinated challenged broiler groups (especially G4) and in the vaccinated challenged SPF group (G8) as compared to their control non-vaccinated challenged groups, G2, G5 and G9, respectively. Additionally, the histopathological and immunohistochemical examinations indicated significantly higher protection in the vaccinated-challenged broilers (G1 and G4) and SPF (G8) groups in comparison to their controls. Overall, this study demonstrated higher protective efficacy of rHVT + IBD + H5 hatchery vaccination against Egyptian nVArIBDV, A2dB1b, especially in the broiler chickens G4 that had specific MDA.