Avian infectous bronchitis (IB)
IB virus is caused by Infectious bronchitis virus of the genus Coronavirus in the family Coronaviridae, which is a positive sense ssRNA virus. It occurs in many antigenic variants as a consequence of mutations in its large genome.
Epidemiology: IB virus spreads between birds by aerosol and by ingestion of food contaminated with feces.
Clinical signs: This is an acute, rapidly spreading disease of young chicks, chiefly under 4 weeks of age. Occasionally, older birds are attacked in mild form. Mortality is very high among young birds. Fowls are the only known species of birds susceptible to this disease. The symptoms include gasping, coughing and crackling breathing, watery discharge from the nose, sometimes with a swelling of the sinuses. The course of the disease may be rapid with most of the birds contracting the infection and recovering within a week or 10 days, or it may persist for as long as 3 weeks. Laying of poor quality eggs having weak shell and abnormal shape may persist for several weeks in layers.
Diagnosis: It is diagnosed by the isolation of the virus in embryonated chicken eggs, cross serum-neutralization and cross immunity tests. Postmortem examination reveals catarrhal tracheitis, bronchitis and air sacculitis with slight thickening and clouding of the air sac membranes. The fluorescent antibody test on the scrapings from trachea, complement fixation, passive haemagglutination and immunodiffusion tests provide confirmatory diagnosis. In some laboratories PCR or DNA probes are also being used.
Treatment, prevention and control: Rise in room temperature from 3 to 6 C may lower mortality rate. Food consumption should be stimulated by all possible means. Immunization may be carried out by the use of modified live virus vaccines, which produces relatively mild respiratory symptoms. These vaccines are usually administered through drinking water or as a dust or spray. It generally takes about 3 weeks for most of the birds to acquire a high degree of immunity following vaccination