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

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.