Pathogenicity differences between a newly emerged TW-like strain and a prevalent QX-like strain of infectious bronchitis virus.

TW-like IBV isolates have appeared frequently in recent years in mainland China. In this study, we compared the TW-like IBV GD strain and the predominant QX-like SD strain in terms of serology and pathogenicity to 3-week-old specific-pathogen-free chickens. Both strains could cause severe respiratory distress and renal lesions, with a mortality rate were approximately 20%. Virus were continuously shed via the respiratory tract and cloaca. However, the infection pattern of the two isolates were different. The GD strain persisted for a longer duration and caused extensive damages to the tracheas and lungs. Moreover, chickens infected with the GD strain showed inefficient recovery of damaged cilia after infection. Our findings suggested that the newly emerged TW-like IBV GD strain showed obvious differences in pathogenicity, tissue tropism and replication efficiency compared with the QX-like IBV SD strain, with the TW-like GD strain showing stronger tropism to the respiratory tract and a longer duration of clinical signs.