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Infectious Bronchitis
Cause
Infectious bronchitis virus. Neutralization tests in chicken embryos have shown there are many antigenic types of the virus. They are not related antigenically to other coronavirus species.
Occurrence
This highly contagious disease of chickens occurs worldwide.
Transmission
The virus is present in respiratory discharges and transmission is by direct and indirect contact and aerosol.
Clinical & Pathologic Features
Infectious bronchitis is a highly contagious disease of sudden onset and high morbidity. The disease is most severe in chicks and young birds; older birds are susceptible, although the disease is mild. Mortality may be high in baby chicks infected with nephrotropic strains.
The cardinal clinical signs are coughing and gasping. Changes include cloudiness of the air sacs, exudative bronchitis, and excess serous or catarrhal exudate in the trachea.
Principal loss in affected flocks is the lowered egg production. The egg-laying capacity of survivors may be permanently impaired; eggs may be misshapen, rough, and soft-shelled. Some strains of the virus are nephrotrophic and cause interstitial nephritis with sudden death.
Diagnosis
• Clinical specimens: Trachea, lungs, and kidneys.
• The virus can be cultivated in susceptible chicken embryos and in chicken epithelial cell cultures. Serotype identification is accomplished by virus neutralization tests with specific antisera.
• The changes occurring in the inoculated embryos are usually seen after several passages. They are characterized by death or dwarfing, curling of the embryo, and crystal urate deposits in the meso-nephrons.
• Fluorescent antibody tests on tracheal scrapings from infected birds have been used for rapid diagnosis.
Prevention
• Vaccination is practiced widely. A live attenuated virus is usually administered to birds at 1 - 2 weeks of age via drinking water with revaccination 3 - 4 weeks later, often with a killed vaccine injected subcutaneously. Since there are numerous types of virus, the vaccine used should include the appropriate type(s) for a given area. All rights reserved. This document is available on-line at www.ivis.org. Document No. A3424.1205
