Construction and efficacy of a recombinant QX-like infectious bronchitis virus vaccine strain

Infectious bronchitis (IB) is a highly contagious disease caused by the avian infectious bronchitis virus (IBV). This disease mainly causes damage to the respiratory system and has brought serious harm to the poultry industry in China. At present, QX-like IBV is the most prevalent strain in China, which is highly pathogenic and causes severe nephritis. Based on the construction of the H120 infectious clone, this study successfully constructed and rescued the recombinant virus H120-S1/LMH by using RED/ET recombination engineering technology combined with ccdB reverse selection to replace the S1 gene of the H120 infectious clone with the S1 gene of the prevalent IBV LMH strain. The recombinant virus showed good genetic stability and propagation in 15 continuous generations on chick kidney cells (CK cells). To evaluate the protection of this candidate vaccine strain, we conducted a vaccination challenge test. The specific-pathogen-free (SPF) chicks were immunized at 3 days of age and challenged with the QX-like IBV virulent strain LMH after 14 days. The results showed that the recombinant virus could provide 90% protection against the virulent IBV LMH strain, and mortality was significantly reduced, indicating the potential of H120-S1/LMH as a candidate vaccine. This study provides a strategy for precisely and rapidly generating IBV vaccine candidates by reverse genetics and lays a foundation for the further development of a new IBV vaccine against prevalent strains.