Infectious Bronchitis

Agent, Infection, and Disease. Infectious bronchitis is caused by the avian coronavirus, infectious bronchitis virus (IBV), which is found worldwide. Infections, depending on the strain, may cause an acute upper‐respiratory tract disease, drops in egg production, decreased egg quality, and nephritis. The virus is transmitted by inhalation or direct contact with contaminated objects and morbidity is usually 100%; whereas, mortality can vary depending on a variety of host factors and the strain of the infecting virus. Chickens are the primary host but the virus has also been found in pheasants and peafowl. There exist many different antigenic types of the virus and due to a high rate of mutation, new antigenic variants constantly emerge. As a general rule, different antigenic types and variants have little to no cross‐protection. Diagnosis. The preferred diagnostic test is molecular detection of the viral spike (S1) gene or virus isolation in embryonating chicken eggs. Multiple antigenic types of the virus are identified by sequence analysis of the S1 gene or by the virus neutralization test using serotype‐specific antibodies. The disease can also be diagnosed by demonstrating rising antibody titers against IBV between preclinical and convalescent sera. Intervention. Attenuated live and killed vaccines are used in an attempt to control the disease. However, multiple different antigenic types and constantly emerging new types that do not cross‐protect make it difficult to prevent transmission and disease