Comprehensive Report on Variant Infectious Bursal Disease Virus (IBDV) and Vaccine Challenges
Dr. Majed Hamed Al Sayeg / poultry pathologist / Australia
Introduction
Infectious Bursal Disease (IBD), also known as Gumboro disease, is a highly contagious disease that causes immunosuppression in poultry. It is caused by the Infectious Bursal Disease Virus (IBDV), a non-enveloped RNA virus of the genus Avibirnavirus. The virus targets the bursa of Fabricius in chickens, increasing susceptibility to secondary infections. Recent studies have identified the emergence of variant IBDV strains, posing new challenges for disease control and vaccination programs.
Variant IBDV / Emergence and Molecular Characteristics
Detection of Variant Strains: Recent studies have revealed the presence of variant IBDV strains, such as genotype A2dB1b, which were previously confined to specific regions. These strains cause subclinical infections characterised by bursal atrophy and immunosuppression, complicating diagnosis and increasing the risk of secondary infections.
Genetic Mutations: Variant strains exhibit mutations in key antigenic sites, such as the VP2 and VP1 genes, including notable mutations like A321V in VP2 and R511K, S687P, and T859I in VP1. These mutations affect the virus’s pathogenicity and immune evasion mechanisms.
Spread and Epidemiology: The emergence of these strains underscores the need for enhanced molecular surveillance to track their spread and adapt control strategies accordingly.
Challenges with Traditional Vaccines /Limited Efficacy
Antigenic Mismatch: Traditional vaccines are primarily designed using classical or very virulent IBDV (vvIBDV) strains. However, variant strains like A2dB1b exhibit significant antigenic differences, reducing the vaccines’ effectiveness.
Partial Protection: While traditional vaccines may offer some level of immunity, they often fail to provide full protection against variant strains due to their inability to neutralise these antigenically distinct viruses.
Immunosuppressive Impact: Variant IBDVs, such as A2dB1b, cause immunosuppression, which may reduce the overall effectiveness of vaccines and complicate efforts to control the disease’s spread.
Emergence of Escape Mutants :Repeated use of traditional vaccines leads to the development of escape mutants, further diminishing the efficacy of vaccination programs.
Field Observations : Reports from affected regions highlight poor vaccine performance against outbreaks caused by variant strains, emphasising the need for improved vaccine formulations.
Developing New Vaccines for Variant IBDV / Promising Approaches
Reassortant Vaccines: These vaccines incorporate genes from variant strains, such as VP2 and VP1, to enhance antigenic matching and provide better protection.
Virus-Like Particle (VLP) Vaccines: VLP-based vaccines have demonstrated high efficacy and safety in trials targeting variant strains.
Advanced Platforms: Emerging technologies, such as mRNA and protein subunit vaccines, offer precise antigenic matching, although they remain in developmental stages.
Integrated Control Strategies
Enhanced Surveillance: Comprehensive molecular studies are essential to track the spread of variant strains and update vaccine formulations.
Local Production: Establishing local vaccine production facilities can enable rapid responses to emerging variants and reduce reliance on imported vaccines.
Biosecurity Improvements: Strengthening hygiene practices and biosecurity measures is vital to complement vaccination efforts.
Research Priorities
Pathogenicity Studies: Conducting experimental trials to assess the severity of diseases caused by variant strains and their impact on poultry health and vaccine efficacy.
Antigenic Mapping: Detailed analysis of VP2 and VP1 epitopes to guide the design of next-generation vaccines.
Genomic Databases: Establishing a genetic database to track real-time changes in variant strains.
Policy and Funding
Regional Collaboration: Strengthening cooperation among specialised institutions can improve resource sharing and policy coordination to combat IBDV effectively.
Increased Funding: Investing in veterinary research and vaccine development is crucial to address challenges posed by variant strains.
Conclusion : The emergence of variant IBDV strains presents significant challenges to poultry health and production. These strains exhibit reduced vaccine efficacy due to their antigenic divergence, highlighting the urgent need for new vaccine technologies. By fostering scientific research, enhancing surveillance, and strengthening regional cooperation, the poultry industry can better address the impact of IBDV and ensure sustainable production.
