Coronavirus is the causal agent. Several different serotypes of IB virus are known to exist. Only chickens are susceptible to IB virus.
The virus is transmitted from bird to bird through the airborne route. The virus can also be transmitted via air between chicken houses and even from farm to farm. Especially multi age farms are at risk.
In young chicks IB virus infection causes the formation of cheesy exudates in the bifurcation of the bronchi, thereby causing asphyxia and followed by severe respiratory distress ("pump handle" breathing). In older birds, IBV does not cause mortality. Respiratory signs include wet rales, gurgling, and wheezing. Egg production decreases dramatically, sometimes to zero, and usually does not return to normal levels. Deformed eggs with wrinkled shells and rough surfaces at the top (sand heads) are often observed.
Mucous and hemorrhages in tracheas, froths in airsacs in older chickens. In young chicks a yellow cheesy plug at the tracheal bifurcation is indicative of IB infection.
There are 3 main factors to be considered in order to arrive at a diagnosis
The clinical picture including post-mortem findings in the flock, isolation of the virus in the laboratory, and a rising antibody titre when the serum is tested against a known strain of bronchitis virus.
Treatment and control
There is no treatment for infectious bronchitis. Secondary bacterial infections may be prevented by treatment with antibiotics. Prevention by vaccination is the best method to control IB.