Avian infectious bronchitis (IB)

An acute, highly contagious respiratory disease of chicken caused by a member of the family Coronaviridae, IB was first recognized in India in 1969. The virus can be propagated in 10-day-old embryonated chicken eggs resulting in dwarfing and curling of embryos. Transmission occurs through direct contacts, aerosol and contaminated fomites. Transovarian transmission does not occur. Birds of all ages are susceptible but chicks below 4 weeks of age are severely affected.

Symptoms and lesions: Clinically the birds show depression and respiratory distress like coughing, gasping, sneezing and discharges from the eyes and nostrils. Sometimes the respiratory signs may be too mild to be noticed. The virus at times attacks the oviduct and the kidney, resulting in significant reduction in egg production and poor quality eggs. Early infection of the chicks may result in damage to oviduct and such birds fail to lay eggs. Infection of layers leads to lowered egg production and eggs laid may be misshapen, rough, soft shelled and with poor hatchability. In young chicks mortality may go upto 25%. In the renal form of the disease mortality may occur in broilers. Recovered birds may act as carriers for several days. The PM lesions seen are congestion of lungs and cloudy air sacs, catarrhal exudates or caseous plugs in the trachea and on lungs. When there is involvement of oviduct, regression of size and absence of duct are seen. When nephropathic strains are involved the kidney may be swollen and pale with tubules and ureters distended with urates.

Diagnosis: Clinical symptoms and lesions are indicative of infection. Final confirmation is done on the basis of isolation and identification of the virus. Virus can be isolated in 10-11 day old chicken embryos inoculated with trachea, caecal tonsils and oviduct and kidney tissue homogenate from suspected birds.

Prevention and control: Proper hygiene and good management is necessary. Live vaccines are used in broilers and for initial vaccination of breeders and layers. Inactivated oil adjuvanted vaccines are primarily used at the point of lay in breeders and layers. Best protection with inactivated vaccine can be obtained only if it is given after priming the birds with live vaccines.