Pathogenicity of a GI-22 genotype infectious bronchitis virus isolated in China and protection against it afforded by GI-19 vaccine.

Avian infectious bronchitis (IB) is a globally circulating bird disease caused by infectious bronchitis virus (IBV). In China, the most prevalent IBV genotype is GI-19/QX-like because the protective efficiency of the classical IBV vaccine is low, and new GI-19 vaccines are under development. In 2018, a GI-22 genotype strain CK/CH/LGD/2018 (abbreviated 'LGD') was isolated in northern China, which caused 10%-30% morality in H120-vaccinated chickens. A phylogenetic analysis showed that this new isolate displays novel features compared with other earlier-isolated reference strains. To monitor the epidemic trend of IBV in China, the pathogenicity of LGD was first evaluated in 1-day-old specific-pathogen-free chickens. LGD induced classical IBV damage in the trachea and kidney, whereas it also infected and damaged the bursa of Fabricius, an important immune organ of chickens. The efficacy of our earlier-developed GI-19 vaccine, strain SZ200, against LGD was also evaluated in this study. The GI-19 genotype vaccine provided sufficient protection against the new GI-22 genotype strain, and may be a promising candidate vaccine with which to control both wild GI-19 and GI-22 strains in the future.