Avian infectious bronchitis
Encyclopedia
Avian infectious bronchitis (IB) is an acute and highly contagious respiratory disease
of chicken
s. The disease is caused by avian infectious bronchitis virus
(IBV), a coronavirus
, and characterized by respiratory signs including gasping, coughing, sneezing, tracheal
rales
, and nasal discharge. In young chickens, severe respiratory distress
may occur. In layers, respiratory distress, nephritis
, 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.
described and varies greatly genetically and phenotypically, with hundreads of serotypes and strains described. Coronaviruses contain the largest known viral RNA genome in number of nucleotides, of approximately 30,000 bases. The RNA forms a single strand and single segment. IBV diversity is based on transcriptional error, which may become very relevant if occurring in genomic sequences coding for proteins, involved in adsorption to target cell or inducing immune responses. Transcriptional error variants may emerge with evolutional advantage in susceptible chickens. Large genomic changes will occur with entire gene interchanges, by reassortment, as for its replication, seven subgenomic mRNAs are produced and will enable reassortment in coinfections.
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.
Read more about clinical AIB here
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
(chronic respiratory disease), Newcastle disease
by mesogenic strains of Newcastle diseases virus (APMV-1), avian metapneumovirus
, infectious laryngotracheitis, avian infectious coryza 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
s of Aspergillus
ochraceus), and dehydration
.
In laying hens, abnormal and reduced egg production are also observed in Egg Drop Syndrome 76 (EDS), cause by an Atadenovirus
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, recent methodology using genomic amplification (PCR) and sequencing of products, will enable very precise description of strains, according to the oligonucleotide
primers designed and target gene. 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
and Haemagglutination inhibition (haemagglutinating IBV produced after enzymatic treatment by phospholipase C).
Vaccines are available (ATCvet codes: for the inactivated vaccine, for the live vaccine; plus various combinations).
Biosecurity
protocols including adequate isolation
, disinfection
are important in controlling the spread of the disease.
Respiratory disease
Respiratory disease is a medical term that encompasses pathological conditions affecting the organs and tissues that make gas exchange possible in higher organisms, and includes conditions of the upper respiratory tract, trachea, bronchi, bronchioles, alveoli, pleura and pleural cavity, and the...
of chicken
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...
s. The disease is caused by avian infectious bronchitis virus
Avian infectious bronchitis virus
Avian infectious bronchitis virus is a coronavirus which infects chicken, causing the associated disease, infectious bronchitis Avian infectious bronchitis virus (IBV) is a coronavirus which infects chicken, causing the associated disease, infectious bronchitis Avian infectious bronchitis virus...
(IBV), a coronavirus
Coronavirus
Coronaviruses are species in the genera of virus belonging to the subfamily Coronavirinae in the family Coronaviridae. Coronaviruses are enveloped viruses with a positive-sense single-stranded RNA genome and a helical symmetry. The genomic size of coronaviruses ranges from approximately 16 to 31...
, and characterized by respiratory signs including gasping, coughing, sneezing, tracheal
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
rales
Rales
Crackles, crepitations, or rales 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 often heard only with a stethoscope...
, and nasal discharge. In young chickens, severe respiratory distress
Respiratory failure
The term respiratory failure, in medicine, is used to describe inadequate gas exchange by the respiratory system, with the result that arterial oxygen and/or carbon dioxide levels cannot be maintained within their normal ranges. A drop in blood oxygenation is known as hypoxemia; a rise in arterial...
may occur. In layers, respiratory distress, nephritis
Nephritis
Nephritis is inflammation of the nephrons in the kidneys. The word "nephritis" was imported from Latin, which took it from Greek: νεφρίτιδα. The word comes from the Greek νεφρός - nephro- meaning "of the kidney" and -itis meaning "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.
Etiology
IBV was the first coronavirusCoronavirus
Coronaviruses are species in the genera of virus belonging to the subfamily Coronavirinae in the family Coronaviridae. Coronaviruses are enveloped viruses with a positive-sense single-stranded RNA genome and a helical symmetry. The genomic size of coronaviruses ranges from approximately 16 to 31...
described and varies greatly genetically and phenotypically, with hundreads of serotypes and strains described. Coronaviruses contain the largest known viral RNA genome in number of nucleotides, of approximately 30,000 bases. The RNA forms a single strand and single segment. IBV diversity is based on transcriptional error, which may become very relevant if occurring in genomic sequences coding for proteins, involved in adsorption to target cell or inducing immune responses. Transcriptional error variants may emerge with evolutional advantage in susceptible chickens. Large genomic changes will occur with entire gene interchanges, by reassortment, as for its replication, seven subgenomic mRNAs are produced and will enable reassortment in coinfections.
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 oclusion 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.
Read more about clinical AIB here
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
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 gallisepticumMycoplasma gallisepticum
Mycoplasma gallisepticum is a bacterium belonging to the class Mollicutes and the family Mycoplasmataceae. It is the causative agent of chronic respiratory disease in chickens and infectious sinusitis in turkeys, chickens, game birds, pigeons, and passerine birds of all ages.-Transmission:MG is...
(chronic respiratory disease), Newcastle disease
Newcastle disease
Newcastle disease is a contagious bird disease affecting many domestic and wild avian species. First found in Newcastle, United Kingdom in 1926, then by Burnet in 1943 in Australia in connection with laboratory infection where the virus was isolated from a ocular discharge of a patient to show the...
by mesogenic strains of Newcastle diseases virus (APMV-1), avian metapneumovirus
Metapneumovirus
Human metapneumovirus is a negative single-stranded RNA virus of the family Paramyxoviridae and is closely related to the avian metapneumovirus subgroup C. It was isolated for the first time in 2001 in the Netherlands by using the RAP-PCR technique for identification of unknown viruses growing...
, infectious laryngotracheitis, avian infectious coryza in some stages may clinically resemble IB. Similar kidney lesions may be caused by different etiologies, including other viruses, such as infectious bursal disease
Infectious Bursal Disease
Infectious bursal disease is a highly contagious disease of young chickens caused by infectious bursal disease virus , characterized by immunosuppression and mortality generally at 3 to 6 weeks of age. The disease was first discovered in Gumboro, Delaware in 1962...
virus (the cause of Gumboro disease) and toxins (for instance ochratoxin
Ochratoxin
Ochratoxins are a group of mycotoxins produced by some Aspergillus species and Penicillium species including Aspergillus ochraceus and Penicillium viridicatum...
s of Aspergillus
Aspergillus
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...
ochraceus), and dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
.
In laying hens, abnormal and reduced egg production are also observed in Egg Drop Syndrome 76 (EDS), cause by an Atadenovirus
Atadenovirus
Atadenoviruses infect animals with a broad host range from several vertebrate classes .-Types of Atadenovirus:Referenced from *Bovine adenovirus D**Bovine adenovirus 4**Bovine adenovirus 5**Bovine adenovirus 8...
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, recent methodology using genomic amplification (PCR) and sequencing of products, will enable very precise description of strains, according to the oligonucleotide
Oligonucleotide
An oligonucleotide is a short nucleic acid polymer, typically with fifty or fewer bases. Although they can be formed by bond cleavage of longer segments, they are now more commonly synthesized, in a sequence-specific manner, from individual nucleoside phosphoramidites...
primers designed and target gene. Methods for IBV antigens detection may employ labelled antibodies, such as direct immunofluorescence or immunoperoxidase. Antibodies to IBV may be detected by indirect immunofluorescent
Immunofluorescence
Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...
antibody test, ELISA
ELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
and Haemagglutination inhibition (haemagglutinating IBV produced after enzymatic treatment by phospholipase C).
Treatment and prevention
No specific treatment is available, but antibiotics can be used to prevent secondary infections.Vaccines are available (ATCvet codes: for the inactivated vaccine, for the live vaccine; plus various combinations).
Biosecurity
Biosecurity
Biosecurity is a set of preventive measures designed to reduce the risk of transmission of infectious diseases, quarantined pests, invasive alien species, living modified organisms...
protocols including adequate isolation
Isolation (health care)
In health care, isolation refers to various measures taken to prevent contagious diseases from being spread from a patient to other patients, health care workers, and visitors, or from others to a particular patient...
, disinfection
Disinfection
Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. Disinfection does not necessarily kill all microorganisms, especially nonresistant bacterial spores; it is less effective than sterilisation, which is an extreme physical...
are important in controlling the spread of the disease.
Complete details of IBV
- Avian Infectious Bronchitis expert reviewed and published by Wikivet, accessed 07/10/2011.
- The disease in the Merck Veterinary Manual
- The Infectious Bronchitis (IB) information site