Limited Protection Conferred by Recombinant Newcastle Disease Virus Expressing Infectious Bronchitis Spike Protein

Area of Science:

• Veterinary Virology
• Vaccine Development
• Avian Immunology

Background:

• Infectious bronchitis virus (IBV) causes significant economic losses in the poultry industry.
• Newcastle disease virus (NDV) is a potential vector for delivering heterologous antigens.
• Recombinant NDV expressing IBV spike (S)-ectodomain (rLS/IBV.Se) was developed to confer protection against IBV.

Purpose of the Study:

• To evaluate the protective efficacy of rLS/IBV.Se against IBV challenge in chickens.
• To assess the impact of vaccination schedule and dose on immune responses and protection.

Main Methods:

• Chickens were vaccinated with rLS/IBV.Se at different ages (day 1, day 10, or day 1 and 14) and doses (10^4 or 10^7 EID50/bird).
• Vaccinated chickens were challenged with virulent Arkansas-type IBV strains.
• Clinical signs, tracheal lesions, viral loads (lachrymal fluids, trachea), and antibody responses (NDV and IBV S1) were assessed.

Main Results:

• A single vaccination with a low dose (10^4 EID50) was ineffective.
• Higher dose (10^7 EID50) and boosting improved protection, reducing clinical signs and tracheal lesions.
• Vaccination on day 10 post-hatch induced significantly higher IBV S1 antibody responses compared to day 1.
• Neither vaccination regimen reduced viral loads in lachrymal fluids or trachea.

Conclusions:

• Recombinant NDV expressing IBV S-ectodomain provides partial protection against IBV challenge, indicated by reduced clinical signs and lesions.
• Vaccination timing and dose influence the immune response, with later vaccination (day 10) and higher doses being more effective.
• Further research is required to enhance protection and achieve viral load reduction in the upper respiratory tract.