Occurrence and Economic Significance
Infectious bronchitis (IB) occurs world wide and is responsible for depressed egg production and shell quality in susceptible commercial and breeder flocks. Infection of immature chickens causes a mild respiratory disease which may affect liveability and growth if exacerbated by adverse managemental and climatic stress or intercurrent mycoplasmosis.

Transmission
The virus can be transmitted from clinically affected birds to susceptible flocks by direct contact and indirectly on fomites.

Clinical Signs
Moderate morbidity and low flock mortality associated with respiratory rales (gurgling and snicking) and ocular discharge. Mature flocks show reduced egg production with malformed shells.

Pathology
Hyperemia (red discoloration) of the trachea and accumulation of mucus in the nasal cavity. Chronic cases, complicated by secondary E. coli infection show airsacculitis.

Diagnosis
The diagnosis can be confirmed by isolation and identification of the causal virus using egg inoculation or tissue culture techniques.

Retrospective diagnosis is possible by demonstrating a significant rise in circulating antibody in paired acute and recovery-phase sera applying ELISA or SN assay.

Prevention
Immature breeding and commercial layer flocks are routinely vaccinated with a mild attenuated product (H-120, or Massachusetts or Connecticut or their combination) at 7 days in drinking water or by aerosol. The vaccination is repeated at 30-40 days. The initial live vaccine should always be administered to susceptible breeder and layer flocks before 12 weeks of age to avoid possible damage to the developing reproductive tract of the pullet. Immunity in commercial layers can be boosted by administration of live attenuated vaccine in drinking water or as a coarse spray during the production period. Potential breeder flocks receive inactivated IB vaccine as a booster, usually in the form of an injectable multivalent emulsion at the end of the rearing period and then at mid-cycle as considered necessary to maintain adequate maternal antibody transfer to progeny.

Broilers in endemic areas are vaccinated by aerosol at day-old or subsequently by coarse spray or in drinking water at a suitable time (10-20 days) depending on maternal antibody transfer or pattern of field challenge.

In some areas special IB vaccines are required to prevent clinical problems attributed to variant strains.

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