''Avian coronavirus'' is a species of virus from the genus '' Gammacoronavirus'' that infects birds; since 2018, all gammacoronaviruses which infect birds have been classified as this single species. The strain of avian coronavirus previously known as infectious bronchitis virus (IBV) is the only coronavirus that infects chickens. It causes

avian infectious bronchitis Avian infectious bronchitis (IB) is an acute and highly contagious respiratory disease of chickens. The disease is caused by avian infectious bronchitis virus (IBV), a coronavirus (Coronaviridae, Orthocoronavirinae, genus ''Gammacoronavirus'', sub ...

, a highly infectious disease that affects the

respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to th ...

, gut, kidney and reproductive system. IBV affects the performance of both meat-producing and egg-producing chickens and is responsible for substantial economic loss within the poultry industry. The strain of avian coronavirus previously classified as Turkey coronavirus causes gastrointestinal disease in turkeys.

Classification

IBV is in the genus '' Gammacoronavirus'', or group 3, with a non-segmented, positive-sense single-stranded RNA genome. It was previously the type species of its genus ''

Igacovirus ''Igacovirus'' is a subgenus of viruses in the genus ''Gammacoronavirus''. Species The genus consists of the following three species: * ''Avian coronavirus'' * ''Avian coronavirus 9203'' * ''Duck coronavirus 2714 ''Duck coronavirus 2714'' is ...

''. When there was only one genus of coronaviruses, the genus ''Coronavirus'', it was the type species of the group of all known coronaviruses.

Recombination

When two strains of

coronavirus Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the com ...

IBV infect a host they may recombine during genome replication. Recombination appears to contribute to the genetic variation of the IBV genome found in nature.

Pathology

Respiratory system

When inhaled, virus will attach to

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...

receptors containing

sialic acid Sialic acids are a class of alpha-keto acid sugars with a nine-carbon backbone. The term "sialic acid" (from the Greek for saliva, - ''síalon'') was first introduced by Swedish biochemist Gunnar Blix in 1952. The most common member of this gr ...

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 ('' Mycoplasma gallisepticum'', avian infectious laryngotracheitis (''

Gallid alphaherpesvirus 1 ''Gallid alphaherpesvirus 1'' (GaHV-1) is a species of virus in the order ''Herpesvirales'', family ''Herpesviridae'', subfamily ''Alphaherpesvirinae'', and genus ''Iltovirus''. Originally recognised in chickens in the United States in 1926, this ...

''), Newcastle disease (avian paramyxovirus 1), '' Avian metapneumovirus'' infection may be confused clinically to infectious bronchitis.

Kidney

Through viremia, some nephrotropic strains (most of high virulence) 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 (the egg-white gland) and in the uterus (the egg-shell gland), leading to a sharp decline of egg production, shell-less, fragile or roughened shells eggs (uterus lesion) with watery whites (magnum lesion). 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.