Histopathology and immunohistochemistry of renal lesions due to avian infectious bronchitis virus in chicks uninoculated and previously inoculated with highly virulent infectious bursal disease virus

A nephropathogenic strain of infectious bronchitis virus (IBV) was inoculated intra-tracheally into 14-day-old specific-pathogen-free chicks or ones previously inoculated with highly virulent infectious bursal disease virus (IBDV) at 7 days of age. The renal lesions were examined histopathologically and immunohistochemically at intervals up to 30 days post-inoculation. The mortality was 20% in the IBDV + IBV-inoculated group, but not in the IBV-inoculated one. Swollen and pale kidneys due to IBV infection were more severe and of longer duration in dually infected chicks. At the early stage of infection, the histopathological changes in the kidneys were similar in both groups, but the ducto-tubular damage was more severe in the dually infected chicks. At the late stage of infection, the renal lesions were characterized by chronic interstitial nephritis with formation of lymphoplasmacytic nodules in IBV-inoculated chicks and by chronic active nephritis which consisted of tubular degeneration, lymphoid cell reaction and interstitial fibrosis in IBDV + IBV-inoculated ones. More IBV antigen-positive cells persisted longer in the kidneys of dually infected chicks than in those of IBV-inoculated ones.