The Pathology of Infectious Bronchitis.

Infectious bronchitis (IB) is an acute disease of chickens caused by a gammacoronavirus, infectious bronchitis virus (IBV). Infection of the nasal and tracheal mucosa causes a rapid loss of ciliated epithelium and impaired mucociliary clearance that predispose chickens to secondary bacterial infections. In poultry production, disease progression and severity are influenced by other live virus vaccines, immunosuppression, and coexisting pathogens. The digestive tract supports viral replication in the proventriculus, intestines, cloaca, and the bursa of Fabricius. Acute enteritis and stunted growth in young chickens are caused by an enterotropic IBV. IBV spreads systemically by infection of tracheal macrophages and blood monocytes, deep respiratory infections, and potentially ascending viral infection from the cloaca. Nephrotropic IBV causes severe disease in the kidney with necrosis of tubular epithelial cells, inflammation, and renal failure. Viral infection of the female reproductive tract in the first 2 weeks of life causes necrosis and scarring of the oviduct mucosa, resulting in a chronic cystic oviduct that precludes egg formation when the hen matures. Virus infection of mature hens causes necrosis and inflammation of the oviduct mucosa, leading to the deterioration of egg quality and transient interruption of egg production. In males, IBV infection of seminiferous tubules in the testicle and efferent ductules in the epididymis results in epididymitis and epididymal lithiasis, decreases in sperm production and fertility, and viral shed to semen, leading to venereal transmission. The role IBV in gastrointestinal and urogenital disease merits further study.