Avian infectious bronchitis

Signs appear within 1-2 days. Young chicks and broilers cough, sneeze and have tracheal rattles, huddle, eat less and grow poorly. Nephropathogenic strains progress to wet droppings, increased thirst and deaths. In laying flocks egg production can fall by up to 70%, with thin, soft, wrinkled, misshapen or pale-shelled eggs and watery whites, and recovery can take up to 8 weeks. At necropsy there is serous to caseous exudate in the trachea, sinuses and nasal passages, cloudy thickened air sacs, and swollen pale kidneys with urates in the tubules and ureters; secondary E. coli adds airsacculitis, perihepatitis and pericarditis.

Avian infectious bronchitis is caused by infectious bronchitis virus, a Gammacoronavirus (family Coronaviridae) with a non-segmented, positive-sense RNA genome. After being inhaled or swallowed it replicates first in the upper respiratory tract, stopping the beating of the tracheal cilia, and then reaches the air sacs, sinuses, kidneys and reproductive tract. Nephropathogenic strains cause interstitial nephritis with urate build-up in the tubules and ureters, and later chronic nephritis. Infection of the oviduct in very young chicks can leave permanent cystic damage, so hens ovulate normally but never lay properly. The virus also persists in the caecal tonsils and is shed in faeces for weeks. The spike (S1) protein varies between strains, and antigenic types do not cross-protect.

Chickens of all ages are affected, and the disease occurs worldwide; related coronaviruses have been isolated from turkeys, pheasants and guinea fowl. Spread is airborne, by direct contact, and mechanically via equipment, egg-packing materials, manure and farm visitors. Birds shed virus for weeks and possibly up to 20 weeks. New variants arise often. The GI-23 lineage (Variant 2) is a Middle Eastern strain: first found in the Palestinian region in the mid-1990s, it reached Egypt in 1998, Iraq and Iran in 2008, Jordan and Lebanon in 2009 and Turkey in 2010, before spreading to other continents and challenging vaccine protection. No human infection has been reported.

Other respiratory diseases of chickens look alike: infectious laryngotracheitis, infectious coryza and Mycoplasma gallisepticum infection, which can also co-infect and worsen IB. Newcastle disease and avian influenza share its respiratory and egg-laying signs. Clinical signs are not specific, so the respiratory form needs laboratory confirmation by RT-PCR with S1 genotyping, virus isolation, or rising antibody titres; vaccination complicates interpretation, and adenoviruses give embryo lesions indistinguishable from IBV in egg culture.

Upper respiratory tract, trachea (cilia), lungs, air sacs, sinuses, kidneys and ureters, oviduct, caecal tonsils

Live attenuated vaccines in young chicks with revaccination, and inactivated vaccines for breeders and layers after live priming. Match vaccine types to local strains since types do not cross-protect. Biosecurity, good ventilation, low ammonia.

Morbidity is typically 100%. Mortality is about 5% but up to 60% with nephropathogenic strains or secondary bacteria (MSD); GI-23 can kill up to 30% of birds under 3 weeks. No antiviral treatment; supportive care. Early oviduct damage is permanent.