Infectious Bronchitis Virus Population Structure Defines Immune Response and Protection

Area of Science:

• Veterinary Virology
• Immunology
• Poultry Health

Background:

• Understanding the impact of vaccine population genetic structure on immune responses is crucial for improving poultry health.
• Arkansas (Ark) Delmarva Poultry Industry (DPI)-type vaccines and a homogeneous CEK-adapted variant (CEK-ArkDPI) were used to model these effects.

Purpose of the Study:

• To investigate how the genetic structure of infectious bronchitis virus (IBV) vaccines influences immune responses and protection against challenge.
• To compare the efficacy of a heterogeneous commercial vaccine versus a homogeneous adapted vaccine.

Main Methods:

• Chickens were vaccinated with either a commercial ArkDPI vaccine or a homogeneous CEK-ArkDPI vaccine.
• Vaccinated chickens were challenged with a virulent Ark99-type IBV strain (AL/4614/98).
• Viral loads, respiratory signs, tracheal lesions, antibody levels, antibody avidity, and innate immune gene expression were assessed.

Main Results:

• The heterogeneous commercial ArkDPI vaccine was more effective at reducing viral loads, while both vaccines similarly reduced respiratory signs and tracheal lesions.
• The homogeneous CEK-ArkDPI vaccine elicited greater antibody levels and antibody avidity.
• The heterogeneous commercial ArkDPI vaccine induced a stronger innate immune response, indicated by greater mRNA expression of immune genes.

Conclusions:

• Vaccine population structure significantly impacts both adaptive (antibody avidity) and innate immune responses.
• Homogeneous IBV vaccines may favor adaptive immunity, while diverse vaccines can enhance innate immunity and viral clearance.
• Immune pressure from vaccination selects for distinct subpopulations within the challenge virus.