Innovative and more sustainable vaccine strategies for Infectious Bursal Disease control in broilers

Infectious Bursal Disease (IBD), a highly contagious viral infection, poses a significant threat to poultry health and productivity. This thesis investigates innovative and sustainable strategies to control IBD, emphasizing advanced vaccination protocols and molecular virology tools to address challenges posed by viral evolution. The first section provides an overview of the Infectious Bursal Disease Virus (IBDV), focusing on its genomic structure, the roles of segments A and B in pathogenicity, and the immune responses triggered during infection. While humoral immunity is well-documented, the systematic review in the second section explores T-cell dynamics during IBDV infection, revealing their critical role in both acute and chronic phases. This review highlights the need for deeper insights into T-cell subtypes, such as regulatory and gamma-delta T-cells, to enhance prevention strategies. The third section evaluates the efficacy of subcutaneous day-of-hatch vaccination using live IBDV vaccines in commercial broilers with maternally derived antibodies. Three protocols were assessed: an intermediate vaccine strain, an intermediate-plus strain, and an immune-complex vaccine. Findings demonstrate that these vaccines effectively protect against very virulent IBDV, preventing bursal damage and clinical disease. Notably, the intermediate-plus vaccine showed superior efficacy by reducing viral replication in the bursa, potentially decreasing viral shedding and transmission in field conditions. These findings suggest that day-of-hatch vaccination is a feasible strategy for early protection, offering biosecurity and economic benefits. The fourth section applies reverse genetics to study a novel South Australian IBDV variant, SA S328, which has rapidly displaced earlier strains. This variant introduces an additional serine residue in the hypervariable region of the VP2 protein, hypothesized to enhance virulence. Cloning and characterizing the genomic segments of SA S328 revealed mutations potentially influencing replication and pathogenicity. This thesis integrates diverse approaches to address key challenges in IBD control, offering insights into improving vaccine strategies and managing evolving viral threats.