Avian infectious bronchitis: cross-protection studies using different Australian subtypes

Area of Science:

• Veterinary Virology
• Immunology
• Poultry Health

Background:

• Infectious Bronchitis Virus (IBV) is a significant respiratory pathogen in poultry.
• Understanding cross-immunity between IBV strains is crucial for effective vaccination strategies.
• Current vaccines (Vac 3, Vac 4) and field strains (Q1/76, N2/62) were evaluated.

Purpose of the Study:

• To assess the cross-protective immunity in chickens vaccinated with different IBV strains.
• To evaluate the correlation between humoral antibody responses and protection against IBV challenge.
• To compare the efficacy of current vaccine strains versus field strains in conferring cross-immunity.

Main Methods:

• Chickens were vaccinated with four distinct IBV strains: Vac 3, Vac 4, Q1/76, and N2/62.
• Vaccinated chickens were subsequently challenged with IBV N1/62 (T0) and IBV N9/74 (Appin).
• Humoral antibody responses and ciliary activity in tracheal rings were measured to assess protection.

Main Results:

• A lack of correlation was observed between humoral antibody levels and the degree of protection.
• Cross-immunity was demonstrated following vaccination with each tested IBV subtype.
• Vaccination with Q1/76 and N2/62 conferred higher levels of cross-immunity compared to Vac 3 and Vac 4.

Conclusions:

• Humoral antibody titers are not a reliable indicator of protection against IBV challenge.
• The efficacy of cross-immunity varies significantly among different IBV vaccine and field strains.
• Field strains Q1/76 and N2/62 appear to induce broader cross-protection than current vaccine strains Vac 3 and Vac 4.