Preparation and protective efficacy of a chicken embryo kidney cell-attenuation GI-19/QX-like avian infectious bronchitis virus vaccine

Avian infectious bronchitis (IB) is a highly contagious disease, and hazardous to the poultry industry. Immune failure often occurs due to the emergence of new serotypes or field strains antigenically different from the vaccine strains. To prepare a candidate vaccine against the prevalent avian infectious bronchitis virus (IBV) in China, the GI-19/QX-like field isolate Sczy3 was selected as the progenitor strain and attenuated via passaging in chicken embryo kidney (CEK) cells for 100 times. The 100th generation of CEK-adapted strain, designated SczyC100, was safe to use on one-day old specific pathogen-free (SPF) chicken as determined by pathogenicity and virulence reversion test. The efficacies of SczyC100 and two commonly used commercial vaccines (H120 and 4/91) against prevalent GI-19/QX and GI-7/TWI type virulent strains were evaluated. Sczy3C100 effectively reduced the morbidity, mortality, mean lesion scores (MLSs), and viral load of trachea of chickens challenged by GI-19/QX and GI-7/TWI strains. CEK-adapted SczyC100 is therefore a potential vaccine candidate for the control of IB in China.