Avian coronavirus


Avian coronavirus is a coronavirus that infects birds, causing the associated disease avian infectious bronchitis. It is a highly infectious avian pathogen that affects the respiratory tract, gut, kidney and reproductive systems of chickens.
IBV affects the performance of both meat-producing and egg-producing chickens and is responsible for substantial economic loss within the poultry industry.

Classification

IBV is in the genus Gammacoronavirus, or group 3, with a non-segmented, positive-sense single-stranded RNA genome.
It is the type species of its Genus Igacovirus, today. And, when there was only one genus in the Coronaviruses, the genus Coronavirus, it was the type species of the group of all known coronaviruses.

Pathology

Respiratory system

When inhaled, virus will attach to glycoprotein receptors containing sialic acid on ciliated epithelial cells of the respiratory epithelium. The respiratory replication will result in loss of ciliary activity, mucus accumulation, necrosis and desquamation, causing respiratory distress, râles and asphyxia. Local virus replication will result in viremia, spreading the infection into other tissues and organs. Other respiratory diseases of chickens, Newcastle disease, Avian metapneumovirus infection may be confused clinically to infectious bronchitis.

Kidney

Through viremia, some nephrotropic strains could infect the kidney epithelium in tubules and nephron, causing kidney failure. At gross examination, kidneys may appear swollen and pale in color and with urates in ureters

Reproductive system

In hens, the viremic IBV will also reach the oviduct, causing lesions in the magnum and in the uterus, leading to a sharp decline of egg production, shell-less, fragile or roughened shells eggs with watery whites. Infection of chickens at puberty, during the oviduct development, will impede oviduct formation and destroy future laying capacity, resulting in "false layers". However, other diseases affecting layer chickens could lead to that condition.

Vaccines

There are both attenuated vaccines and inactivated vaccines available. Their effectiveness is diminished by poor cross-protection. The nature of the protective immune response to IBV is poorly understood, but the surface spike protein, the amino-terminal S1 half, is sufficient to induce good protective immunity. Experimental vector IB vaccines and genetically manipulated IBVs—with heterologous spike protein genes—have produced promising results, including in the context of in ovo vaccination.