Avian infectious bronchitis (IB) is an acute and highly contagious

respiratory disease Respiratory diseases, or lung diseases, are pathological conditions affecting the organs and tissues that make gas exchange difficult in air-breathing animals. They include conditions of the respiratory tract including the trachea, bronchi, bro ...

chicken The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adu ...

s. The disease is caused by

avian infectious bronchitis virus ''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 kn ...

(IBV), a

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 co ...

(Coronaviridae,

Orthocoronavirinae 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 c ...

, genus ''Gammacoronavirus'', subgenus ''Igacovirus''), and characterized by respiratory signs including gasping, coughing, sneezing, tracheal

rales Crackles are the clicking, rattling, or crackling noises that may be made by one or both lungs of a human with a respiratory disease during inhalation. They are usually heard only with a stethoscope ("on auscultation"). Pulmonary crackles are a ...

, and nasal discharge. In young chickens, severe

respiratory distress Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing disc ...

may occur. In layers, respiratory distress,

nephritis Nephritis is inflammation of the kidneys and may involve the glomeruli, tubules, or interstitial tissue surrounding the glomeruli and tubules. It is one of several different types of nephropathy. Types * Glomerulonephritis is inflammation ...

, decrease in egg production, and loss of internal (watery egg white) and external (fragile, soft, irregular or rough shells, shell-less) egg quality are reported.

Clinical signs

Coughing and rattling are common, most severe in young, such as broilers, and rapidly spreading in chickens confined or at proximity. Morbidity is 100% in non-vaccinated flocks. Mortality varies according to the virus strain (up to 60% in non-vaccinated flocks). Respiratory signs will subdue within two weeks. However, for some strains, a kidney infection may follow, causing mortality by toxemia. Younger chickens may die of tracheal occlusion by mucus (lower end) or by kidney failure. The infection may prolong in the cecal tonsils. In laying hens, there can be transient respiratory signs, but mortality may be negligible. However, egg production drops sharply. A great percentage of produced eggs are misshapen and discolored. Many laid eggs have a thin or soft shell and poor albumen (watery), and are not marketable or proper for incubation. Normally-colored eggs, indicative of normal shells for instance in brown chickens, have a normal hatchability. Egg yield curve may never return to normal. Milder strains may allow normal production after around eight weeks. File:Coube pounaedje brontchite-rapt.jpg, Egg yield curve in BI in a parent flock File:Brontchite oûs1.jpg, Thin-shelled egg File:Brontchite oûs2.jpg, Abnormal granulations on shell File:Brontchite oûs3.jpg, Soft-shelled eggs File:Brontchite oûs4.jpg, Misshapen and discolored eggs

Cause

IBV was the first

described and varies greatly genetically and phenotypically, with hundreds of serotypes and strains described. The most updated classification of IBV places the virus in Coronaviridae, Orthocoronavirinae, genus ''Gammacoronavirus'', subgenus ''Igacovirus.'' The coronaviruses contain the largest known viral RNA genome in number of nucleotides, of approximately 30,000 bases. The virions are enveloped and characterized by large surface projections (spikes or S) partially embedded in the double lipid layer. The genome consists of RNA of a single monopartite strand and is coated by the N protein (nucleocapsid). IBV diversity, as for all RNA viruses, may occur as transcriptional error and nucleotide substitution. Nucleotide variants (genotypes), in the gene encoding the distal S protein region (S1), may become very relevant if a different amino acid (non-synonymous) is encoded, and the new phenotype has different biological properties (strain). Amino acid changes located in the receptor binding domain of the S1 spike protein region, involved in the adsorption to the cellular receptor (

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 ...

of cell-surface glycoprotein), may evade neutralization by antibodies, although still capable of adsorption to cell receptor and fusion. As a result of selective pressure, variants may infect chickens with immunity to heterologous variants and emerge with evolutional advantage. In addition, large genomic changes will occur with entire gene segments interchanges by

reassortment Reassortment is the mixing of the genetic material of a species into new combinations in different individuals. Several different processes contribute to reassortment, including assortment of chromosomes, and chromosomal crossover. It is particul ...

, as during IBV replication, seven subgenomic

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...

s are produced, which enable reassortment in coinfections. When two strains of

IBV infect a host cell, reassortment may occur, and appears to contribute to the genetic variation of the IBV

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...

in nature.Wang L, Junker D, Collisson EW. Evidence of natural recombination within the S1 gene of infectious bronchitis virus. Virology. 1993 Feb;192(2):710-6. doi: 10.1006/viro.1993.1093. PMID 8380672

Diagnosis

Chicken respiratory diseases are difficult to differentiate and may not be diagnosed based on respiratory signs and lesions. Other diseases such as mycoplasmosis by ''

Mycoplasma gallisepticum ''Mycoplasma gallisepticum'' (MG) is a bacterium belonging to the class Mollicutes and the family Mycoplasmataceae. It is the causative agent of chronic respiratory disease (CRD) in chickens and infectious sinusitis in turkeys, chickens, game ...

'' (chronic respiratory disease),

Newcastle disease Virulent Newcastle disease (VND), formerly exotic Newcastle disease, is a contagious viral avian disease affecting many domestic and wild bird species; it is transmissible to humans. Though it can infect humans, most cases are non-symptomatic; ...

by mesogenic strains of Newcastle diseases virus ( APMV-1), '' Avian metapneumovirus'', infectious laryngotracheitis, avian infectious coryza '' Avibacterium paragallinarum'' in some stages may clinically resemble IB. Similar kidney lesions may be caused by different etiologies, including other viruses, such as infectious bursal disease virus (the cause of Gumboro disease) and toxins (for instance

ochratoxin Ochratoxins are a group of mycotoxins produced by some ''Aspergillus'' species (mainly ''A. ochraceus'' and A. ''carbonarius'', but also by 33% of ''A. niger'' industrial strains) and some ''Penicillium'' species, especially ''P. verrucosum''. ...

s of ''

Aspergillus ' () is a genus consisting of several hundred mold species found in various climates worldwide. ''Aspergillus'' was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Mic ...

'' ''ochraceus''), and

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

. In laying hens, abnormal and reduced egg production are also observed in

Egg Drop Syndrome 76 An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

(EDS), caused by an

Atadenovirus ''Atadenovirus'' is a genus of viruses, in the family ''Adenoviridae''. Vertebrates serve as natural hosts. There are 10 species in this genus. Taxonomy The genus contains the following 10 species: * ''Bovine atadenovirus D'' * ''Bovine ataden ...

and avian metapneumovirus infections. At present, IB is more common and far more spread than EDS. The large genetic and phenotypic diversity of IBV have been resulting in common vaccination failures. In addition, new strains of IBV, not present in commercial vaccines, can cause the disease in IB vaccinated flocks. Attenuated vaccines will revert to virulence by consecutive passage in chickens in densely populated areas, and may reassort with field strains, generating potentially important variants. Definitive diagnosis relies on viral isolation and characterization. For virus characterization, the methodology using genomic amplification ( PCR), firstly by the reverse transcription of viral RNA into cDNA, the cyclic amplification of cDNA and sequencing of products, will enable very precise description of strains, according to the

oligonucleotide Oligonucleotides are short DNA or RNA molecules, oligomers, that have a wide range of applications in genetic testing, research, and forensics. Commonly made in the laboratory by solid-phase chemical synthesis, these small bits of nucleic acids ...

primers designed and target gene. Broadly sensitive universal gene targets are the nucleoprotein, the matrix or the S2 encoding genes. The S1 encoding gene products sequencing may enable phylogenetic results which are comparable to serotyping. Methods for IBV antigens detection may employ labelled antibodies, such as direct immunofluorescence or immunoperoxidase. Antibodies to IBV may be detected by indirect immunofluorescent antibody test,

ELISA The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay uses a solid-phase type of enzyme immunoassay (EIA) to detect the presen ...

and Haemagglutination inhibition (haemagglutinating IBV produced after enzymatic treatment by phospholipase C).

Treatment and prevention

No specific treatment is available, but

antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and preventio ...

can be used to prevent secondary infections. Different vaccine formulations are available (

ATCvet The Anatomical Therapeutic Chemical (ATC) Classification System is a drug classification system that classifies the active ingredients of drugs according to the organ or system on which they act and their therapeutic, pharmacological and chemical ...

codes: for the inactivated vaccines, typically oil-emulsioned and combined with other avian pathogens, and for the active (live)

lyophilized Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product and lowering pressure, removing the ice by sublimation. This is in contrast to dehydration by most conve ...

strain vaccines, such as H120 and Ma5.

Biosecurity Biosecurity refers to measures aimed at preventing the introduction and/or spread of harmful organisms (e.g. viruses, bacteria, etc.) to animals and plants in order to minimize the risk of transmission of infectious disease. In agriculture, ...

protocols, including adequate distancing of flocks, isolation and

disinfection A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...

are important in controlling the spread of the infection and disease.

References

External links

The Infectious Bronchitis (IB) information site

EM Image of IBV
{{DEFAULTSORT:Avian Infectious Bronchitis Poultry diseases Animal viral diseases Coronavirus-associated diseases