For the chickens inoculated with the QX-like strain rIBYZ, lesions in the trachea at 5 dpi were characterized as cilia necrosis and loss, epithelial cell congestion, hemorrhage, and lymphoid infiltration (Fig. 4 C). In the bronchial and capillary lumen of rIBYZ-infected lungs, congestion, hemorrhage, as well as erythrocyte and inflammatory cell infiltration was observed in some severe cases from 7 to 10 dpi (Fig. 4G). Moreover, erythrocyte and lymphocyte infiltration, as well as tubular dilation was observed in the kidney of rIBYZ-inoculated chickens (Fig. 4K). Similar to the rH120 group, chickens inoculated with rH120-S1/YZ presented with mild pathology in the trachea at the early infection time points of 3, 5 dpi. Lesions in the trachea consisted of the loss of epithelial cells and cilia, decreased number of secretory cells, and thickening of the mucosa (Fig. 4B and D). In contrast, there were no lesions observed in the lungs and kidneys of rH120 and rH120-S1/YZ-infected chickens during the infection period (Fig. F, H, J, and L). No histopathological evidence of damage was detected in the bursa of all the groups and no IBV-associated lesions were found in the tissue samples of the control chickens (Fig. 4A, E, I, M–P).
Fig. 4 Histopathological changes in the trachea, lungs, kidneys, and bursa of SPF chickens infected with the recombinant rH120, rIBYZ, and rH120-S1/YZ strains at 1-day-of-age. Black arrows in the trachea indicate cilia and necrosis loss. Black arrows in the lungs indicate congestion and hemorrhage. Trachea samples were collected at 3, 5 dpi (A–D); lung and bursa samples were collected at 7, 10 dpi (E–H; M–P); and kidney samples were collected at 5, 7 dpi (I–L). Black arrows in kidneys indicate tubular dilation, congestion, and inflammation. Scale bar = 100 μm or 200 μm.