Pathological effect of different avian infectious bronchitis virus strains on the bursa of Fabricius of chickens

Infectious bronchitis is an acute and highly contagious disease caused by avian infectious bronchitis virus (IBV). As well as the typical clinical respiratory signs, such as dyspnoea and tracheal rales, QX genotype strains can also cause damage to the urinary system and reproductive system. Our previous studies found that chickens infected with QX-type IBV also displayed damage to the bursa of Fabricius. To investigate the effects of different genotypes of IBV on the bursa of Fabricius, we challenged one-week-old SPF chickens with Mass, QX and TW genotype IBV strains and compared the clinical signs, gross lesions, histopathological damage, viral loads, and expression levels of inflammatory cytokines (IL-6, IL-8, IL-1ss, IFN-alpha,ss, gamma and TNF-alpha). The results showed that all three strains caused tissue damage, while significant temporal variations in the viral loads of the different infected groups were detected. IBV infection seriously interfered with the natural immune response mediated by inflammatory cytokines (IFN-alpha, IFN-ss, IL-6 and IFN-gamma) in chickens. Our results suggested that IBV has potential immunological implications for chickens that may lead to poor production efficiency.