Pathogenicity and Bioinformatics Analysis of Two GI-13 Infectious Bronchitis Virus Strains in China

Area of Science:

• Veterinary Virology
• Poultry Disease Research
• Molecular Epidemiology

Background:

• Infectious bronchitis virus (IBV) poses a significant threat to the global poultry industry due to its high prevalence and genetic diversity.
• Existing vaccination and control strategies are challenged by the continuous evolution of IBV.
• Novel IBV strains require characterization to understand their impact on poultry health and vaccine efficacy.

Purpose of the Study:

• To characterize two novel GI-13 (4/91-like) IBV field strains, CK/CH/JS/2302 and CK/CH/AH/2307, isolated from vaccinated broiler flocks in China.
• To elucidate the pathogenicity, genomic characteristics, and evolutionary relationships of these IBV strains.
• To assess the potential impact of genetic variations on vaccine cross-protection and inform future vaccine development.

Main Methods:

• Isolation and characterization of IBV field strains from H120-vaccinated broiler flocks.
• Pathogenicity assessment through observation of clinical signs, gross lesions, and mortality rates.
• Whole-genome sequencing and phylogenetic analysis to determine genomic characteristics and evolutionary patterns.
• Sequence and structural modeling of the S1 protein, focusing on hypervariable regions (HVRs).

Main Results:

• Two distinct GI-13 IBV strains, CK/CH/JS/2302 (highly virulent) and CK/CH/AH/2307 (low pathogenic), were identified.
• CK/CH/JS/2302 exhibited a recombinant genome with segments from different IBV genotypes and caused severe symptoms including 10% mortality.
• CK/CH/AH/2307 showed high genomic similarity to the 4/91 vaccine strain but impaired tracheal ciliary activity; amino acid substitutions in S1 HVRs may affect antigenicity and vaccine efficacy.

Conclusions:

• The study demonstrates the coexistence of virulent recombinant and low-pathogenic IBV variants within the same lineage in China.
• Recombination and immune selection are key drivers of IBV evolution, leading to strains that may evade existing vaccine-induced immunity.
• Continuous molecular surveillance and the development of genotype-specific vaccines are crucial for effective control of emerging 4/91-like IBV variants and reducing economic losses in the poultry industry.