Infectious bronchitis in a shamo and ko-shamo breeder farm

In March 2017, some fowls in a 428-day-old Shamo chicken flock of 351, reared in a breeder farm in Shizuoka prefecture, showed signs of respiratory distress, depression, and a drop in egg production. Depression and increased mortality rate were also observed in a 325-day-old Ko-Shamo breeding flock, composed of 185 fowls. All commercial layer flocks of other poultry house in a same farm experienced decline in egg production at the same time. At necropsy, significant gross lesions were not detected in the Shamo chickens. However, histologically, infiltrations of lymphocytes and heterophils were observed in the lamina propria of the bronchial mucosa. In the Ko-Shamo chickens, the kidneys were pale at necropsy. Histological examination revealed degeneration and necrosis of the renal tubules, interstitial infiltrations of lymphocytes and macrophages, and accumulation of spherical crystals in the renal tubular lumen. The specific gene for infectious bronchitis virus (IBV) was detected in both Shamo and Ko-Shamo chickens during virological examination. IBV was isolated from the embryonated chicken eggs inoculated with extracted samples from these chickens. The genotype was classified as JP-I by nucleotide sequence analysis of the S1 protein region. In addition, the serotyping test against antisera of Nerima, TM-86, C78, and AK01 strain showed a neutralization reaction to each serum. Furthermore, the neutralization test using sera collected from pre- and post-infection confirmed increases in antibody titers against these four strains. Based on these results, a diagnosis of infectious bronchitis was made. It was assumed that IBV spread throughout the farm and then caused a drop in egg production among the fowls. Although the Shamo and Ko-Shamo chickens showed different clinical signs and pathological changes in this case, the onset of the disease and the results of the nucleotide sequence analysis indicated that the causative agent was the same viral strain.