Genetic and pathogenic characteristics of a novel infectious bronchitis virus strain in genogroup VI (CK/CH/FJ/202005)

•A novel strain of infectious bronchitis virus (CK/CH/FJ/202005) caused severe air sacculitis in 1- and 15-day-old challenged SPF chickens.•Tracheal and air-sac lesions were first evident at 5 DPI, and persisted throughout the 30-day experiments.•In the 1-day-old infected group, the viral titer in the trachea was above 104 at 5, 7, 10, and 15 DPI, and then dropped rapidly during the third week. Infectious bronchitis virus (IBV) has a significant impact on the poultry industry, and genogroup VI (GVI) IBVs, such as the TC07−2 strain, were reported in China since 2007. We isolated a novel strain, CK/CH/FJ/202005 (henceforth 202005), from broilers that were vaccinated with different attenuated IBV strains (H120, 4/91, or QX) in Fujian, China during 2020. Based on comparison with the SNU8065 strain (GI-22), the 1ab genes were the locations of recombination in this new isolate. Pathogenicity testing of 1-day-old and 15-day-old specific pathogen-free (SPF) chickens indicated varying severities of air sacculitis beginning 5 days-post-inoculation (DPI). Histopathological analysis indicated that tracheal lesions started at 5 DPI and persisted throughout the 30-day experiments in 1-day-old infected chickens. Virus re-isolation and viral load tests indicated this strain was mainly in the trachea, and not the kidneys. Our findings showed that the 202005 strain was pathogenic in 1-day-old and 15-day-old chickens. These results should be considered when developing strategies to control IBV infections.