Characterization of vvIBDV in Vaccinated Broilers and Evaluation of Protection of Different Vaccination Programs

Abstract

Infectious bursal disease (IBD) represents one of the most economically significant diseases affecting young chickens. The objective of this study was to isolate circulating IBDV strains from diseased commercial broiler flocks (n=35) distributed in 7 Egyptian governorates during 2020-2022 and to evaluate the efficacy of different vaccination programs in the protection of commercial broilers against challenge by a very virulent IBDV (vvIBDV) isolate. The detected IBDV were 16 out of 35 (45.7%), from which we selected two pure isolates for a partial sequence of viral protein 2 (VP2). The phylogenetic analysis classified them as A3 genotype, vvIBDV. Experimentally, 135 one-day-old Cobb 500 broilers were used to evaluate 3 vaccination programs against the vvIBDV challenge. Chickens of group 1 (G1) were vaccinated with HVT-IBD vector vaccine, while those in G2 were vaccinated with live intermediate and intermediate plus vaccines (Lukert strain), and G3 were vaccinated with intermediate and intermediate plus vaccines. At the time of the challenge, 28 days of age, each group was subdivided into two categories: vaccinated-challenged (n=15) and vaccinated unchallenged (n=10). Furthermore, 25 broilers in G7 were maintained as a positive control (unvaccinated-challenged) and 25 broilers in G8 were maintained as a negative control (unvaccinated-unchallenged). All vaccination programs are protected from vvIBDV mortality. The vector HVT-IBD vaccine exhibited the greatest performance, the minimal impact on bursal tissue and viral replication, despite a relatively lower antibody titer when compared with classical IBDV vaccines.