Rhinites and conjunctivitis, depression and crowding around heat sources are observed. The death rate could reach 100%. The mortality in young chickens is usually insignificant provided that a secondary infection with a different agent is not occuring.
In such cases, there is a moderate to severe inflammatory cell infiltration of upper respiratory tract mucosa, resulting in thickened and more compact mucosa (Image 1).
Image 1 The thickened and more compact upper respiratory tract mucosa
In layer hens infected with the IB virus, oophoritis and dystrophic necrobiotic lesions affecting primarily the middle and the last thirds of oviduct’s mucous coat are observed. The oviduct is atrophied, cystic, with deposits of yolks or completely formed eggs in the abdominal cavity (the so-called internal layer) (Image 2).
Image 2 Internal layer
The consequences are drop in egg production, apperance and increase in the number of deformed and pigmentless eggs or eggs with soft shells and watery egg white (Image 3).
Image 3 The deformed and pigmentless eggs
IB is caused by a coronavirus. It is characterized by a rich antigenic diversity and that is why many serotypes (Massachusetts, Arkansas 99, Connecticut, O72, etc.) are identified. Often, the infection’s course is complicated with the involvement of E. coli, Mycoplasma gallisepticum, the laryngotracheitis virus, etc.
The nephrotrophic strains of the IB virus cause severe inflammatory (Image 4) and dystrophic necrobiotic damages (Image 5) of kidneys: urolithiasis, interstitial nephritis, haemorrhages that considerably increase the death rate. Under natural conditions, only hens are infected. Non-immnune birds of all ages are susceptible. The disease is even seen in vaccinated flocks.
Image 4 Severe inflammatory in kidney
Image 5 Dystrophic necrobiotic damages of kidney
The serological methods (VN, ELISA, etc.) are widely used in the diagnostics. At present, PCR is used for rapid identification of IB virus serotypes.
IB should be distinguished from other acute respiratory disease as ND, laryngotracheitis and infectious coryza.
The vaccination with live or killed vaccines is effective only if they contain the respective serotype of the virus for the given region.
(Source: "Diseases of poultry - A colour atlas" - Ivan Dinev & CEVA Santé Animal, 2010)