Identification of a Nephropathogenic Strain of Infectious Bronchitis Virus (IBV) in Some Northern Provinces in Vietnam

The nine-day-old Specific Pathogen-Free (SPF) chicken embryos were inoculated with the XDC-2 strain of Infectious Bronchitis Virus (IBV). 50% Embryo Infectious Dose (EID₅₀) and pathological lesions were detected in the developing embryo. At the same time, 18-day-old SPF chickens were inoculated with the same strain of IBV in case of 5 chickens were injected with sterile PBS (1X, pH 7.4) as control and the chickens were checked daily for the symptoms. At 14 days’ post-challenge, all the chicks were slaughtered, the pathological examinations and the virus was detected by RT-PCR. The results indicated that the virus caused dwarfism and death of the embryo after 3 days of post-challenge. The EID₅₀ of the virus was estimated to be 5×10^-5.33/mL. All the experimental chickens showed the symptoms after 3 days of infection such as depression, ruffled feathers, and slight diarrhea. The dead chickens were examined for gross lesions, which showed kidney enlargement, nephropathy, and massive uric acid salt deposits. Histopathological examination revealed that the kidney had tubular ectasia, glassy degeneration of epithelial cells, endothelial cell necrosis and exfoliation in some vessel lumens, monocyte infiltration, hyperemia, and hemorrhage in the renal interstitium. The virus was isolated and detected in the kidney by RT-PCR. It indicated the IBV XDC-2 was a predominantly nephrotoxic infectious bronchitis virus.