Infectious Bursal Disease
Encyclopedia
Infectious bursal disease (also known as IBD, Gumboro Disease, Infectious Bursitis and Infectious Avian Nephrosis) is a highly contagious disease of young chicken
s caused by infectious bursal disease virus (IBDV), characterized by immunosuppression
and mortality generally at 3 to 6 weeks of age. The disease was first discovered in Gumboro, Delaware
in 1962. It is economically important to the poultry industry worldwide due to increased susceptibility to other diseases and negative interference with effective vaccination
. In recent years, very virulent strains of IBDV (vvIBDV), causing severe mortality in chicken, have emerged in Europe
, Latin America
, South-East Asia, Africa
and the Middle East
. Infection is via the oro-fecal route, with affected bird excreting high levels of the virus for approximately 2 weeks after infection.
that has a bi-segmented genome
and belongs to the genus Avibirnavirus of family Birnaviridae
. There are two distinct serotypes of the virus, but only serotype 1 viruses cause disease in poultry. At least six antigen
ic subtypes of IBDV serotype 1 have been identified by in vitro
cross-neutralization assay. Viruses belonging to one of these antigenic subtypes are commonly known as variants, which were reported to break through high levels of maternal antibodies in commercial flocks, causing up to 60 to 100 percent mortality rates in chickens. With the advent of highly sensitive molecular techniques, such as reverse transcription polymerase chain reaction
(RT-PCR) and restriction fragment length polymorphism
(RFLP), it became possible to detect the vvIBDV, to differentiate IBDV strains, and to use such information in studying the molecular epidemiology of the virus.
IBDV genome consists of two segments, A and B, which are enclosed within a nonenveloped icosahedral
capsid
. The genome segment B (2.9 kb) encodes VP1, the putative viral RNA polymerase
. The larger segment A (3.2 kb) encodes viral proteins VP2, VP3, VP4, and VP5. Among them, VP2 protein contains important neutralizing antigenic sites and elicits protective immune response and most of the amino acid
(AA) changes between antigenically different IBDVs are clustered in the hypervariable region of VP2. Thus, this hypervariable region of VP2 is the obvious target for the molecular techniques applied for IBDV detection and strain variation studies.
proteins of some positive-sense single-stranded RNA viruses, such as the nodaviruses and tetraviruses, as well as the T=13 capsid shell protein of the Reoviridae
. The T=13 shell of the IBDV capsid is formed by trimers of VP2, a protein generated by removal of the C-terminal domain from its precursor, pVP2. The trimming of pVP2 is performed on immature particles as part of the maturation process. The other major structural protein, VP3, is a multifunctional component lying under the T=13 shell that influences the inherent structural polymorphism of pVP2. The virus-encoded RNA-dependent RNA polymerase
, VP1, is incorporated into the capsid through its association with VP3. VP3 also interacts extensively with the viral dsRNA genome.
are more susceptible to disease. Birds over eight weeks are resistant to challenge and will not show clinical signs unless infected by highly virulent strains.
After ingestion, the virus destroys the lymphoid follicles in the bursa of Fabricius as well as the circulating B-cells in the secondary lymphoid tissues such as GALT (gut-associated lymphoid tissue), CALT (conjuntiva), BALT (Bronchial) caecal tonsils, Harderian gland
, etc. Acute disease and death is due to the necrotizing
effect of these viruses on the host tissue. If the bird survives and recovers from this phase of the disease, it remains immunocompromised which means it is more susceptible to other diseases.
or immunohistochemistry
tests, based on anti-IBDV labelled antibodies, or in-situ hybridization, based on labelled complementary cDNA sequence probe, are useful for the specific detection of IBDV in infected tissues. RT-PCR (as mentioned above) was designed for the detection of IBDV genome, such as VP1 coding gene, with the possibility of PCR product sequences be determined for genetically comparing isolates and producing phylogenetic trees. Serological tests such as agar gel precipitation and ELISA, for detecting antibodies, are used for monitoring vaccine responses and might be an additional information of infection for unvaccinated flocks.
Necropsy examination will usually show changes in the bursa of Fabricius such as swelling, oedema, haemorrhage, the presence of a creamy transudate and eventually, atrophy. Pathological changes, especially haemorrhages, may also be seen in the muscle, intestines, kidney and spleen.
Passive immunity protects against disease, as does previous infection with avirulent strains. In broiler farms, breeder flocks are immunised against IBD so that they would confer protective antibodies to their progenies, which would be slaughtered for consumption before their passive immunity wears out. The vaccines themselves can cause immunosuppression and damage to the bursa of fabricus. Appropriate hygiene measures are essential for prevention and control as the virus can survive for long periods in both housing and water.
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 caused by infectious bursal disease virus (IBDV), characterized by immunosuppression
Immunosuppression
Immunosuppression involves an act that reduces the activation or efficacy of the immune system. Some portions of the immune system itself have immuno-suppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reaction to treatment of other...
and mortality generally at 3 to 6 weeks of age. The disease was first discovered in Gumboro, Delaware
Gumboro, Delaware
Gumboro is a small unincorporated community in Sussex County, Delaware, USA. It is part of the Seaford, Delaware Micropolitan Statistical Area....
in 1962. It is economically important to the poultry industry worldwide due to increased susceptibility to other diseases and negative interference with effective vaccination
Vaccination
Vaccination is the administration of antigenic material to stimulate the immune system of an individual to develop adaptive immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by many pathogens...
. In recent years, very virulent strains of IBDV (vvIBDV), causing severe mortality in chicken, have emerged in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, Latin America
Latin America
Latin America is a region of the Americas where Romance languages – particularly Spanish and Portuguese, and variably French – are primarily spoken. Latin America has an area of approximately 21,069,500 km² , almost 3.9% of the Earth's surface or 14.1% of its land surface area...
, South-East Asia, Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
and the Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
. Infection is via the oro-fecal route, with affected bird excreting high levels of the virus for approximately 2 weeks after infection.
Virology
IBDV is a double stranded RNA virusRNA virus
An RNA virus is a virus that has RNA as its genetic material. This nucleic acid is usually single-stranded RNA but may be double-stranded RNA...
that has a bi-segmented genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
and belongs to the genus Avibirnavirus of family Birnaviridae
Birnaviridae
The birnaviridae are a family of viruses, including the following genera:*Genus Aquabirnavirus; type species: Infectious pancreatic necrosis virus*Genus Avibirnavirus; type species: Infectious bursal disease virus...
. There are two distinct serotypes of the virus, but only serotype 1 viruses cause disease in poultry. At least six antigen
Antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
ic subtypes of IBDV serotype 1 have been identified by in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
cross-neutralization assay. Viruses belonging to one of these antigenic subtypes are commonly known as variants, which were reported to break through high levels of maternal antibodies in commercial flocks, causing up to 60 to 100 percent mortality rates in chickens. With the advent of highly sensitive molecular techniques, such as reverse transcription polymerase chain reaction
Reverse transcription polymerase chain reaction
Reverse transcription polymerase chain reaction is a variant of polymerase chain reaction , a laboratory technique commonly used in molecular biology to generate many copies of a DNA sequence, a process termed "amplification"...
(RT-PCR) and restriction fragment length polymorphism
Restriction fragment length polymorphism
In molecular biology, restriction fragment length polymorphism, or RFLP , is a technique that exploits variations in homologous DNA sequences. It refers to a difference between samples of homologous DNA molecules that come from differing locations of restriction enzyme sites, and to a related...
(RFLP), it became possible to detect the vvIBDV, to differentiate IBDV strains, and to use such information in studying the molecular epidemiology of the virus.
IBDV genome consists of two segments, A and B, which are enclosed within a nonenveloped icosahedral
Icosahedron
In geometry, an icosahedron is a regular polyhedron with 20 identical equilateral triangular faces, 30 edges and 12 vertices. It is one of the five Platonic solids....
capsid
Capsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
. The genome segment B (2.9 kb) encodes VP1, the putative viral RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
. The larger segment A (3.2 kb) encodes viral proteins VP2, VP3, VP4, and VP5. Among them, VP2 protein contains important neutralizing antigenic sites and elicits protective immune response and most of the amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
(AA) changes between antigenically different IBDVs are clustered in the hypervariable region of VP2. Thus, this hypervariable region of VP2 is the obvious target for the molecular techniques applied for IBDV detection and strain variation studies.
Viral structure
The IBDV capsid protein exhibits structural domains that show homology to those of the capsidCapsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
proteins of some positive-sense single-stranded RNA viruses, such as the nodaviruses and tetraviruses, as well as the T=13 capsid shell protein of the Reoviridae
Reoviridae
Reoviridae is a family of viruses that can affect the gastrointestinal system and respiratory tract. Viruses in the family Reoviridae have genomes consisting of segmented, double-stranded RNA...
. The T=13 shell of the IBDV capsid is formed by trimers of VP2, a protein generated by removal of the C-terminal domain from its precursor, pVP2. The trimming of pVP2 is performed on immature particles as part of the maturation process. The other major structural protein, VP3, is a multifunctional component lying under the T=13 shell that influences the inherent structural polymorphism of pVP2. The virus-encoded RNA-dependent RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
, VP1, is incorporated into the capsid through its association with VP3. VP3 also interacts extensively with the viral dsRNA genome.
Pathogenesis
The virus is attracted to lymphoid cells and especially those of B-lymphocyte origins. Young birds at around two to eight weeks of age that have highly active bursa of FabriciusBursa of Fabricius
In birds, the bursa of Fabricius is the site of hematopoiesis, a specialized organ that, as first demonstrated by Bruce Glick and later by Max Cooper and Robert Good, is necessary for B cell development in birds...
are more susceptible to disease. Birds over eight weeks are resistant to challenge and will not show clinical signs unless infected by highly virulent strains.
After ingestion, the virus destroys the lymphoid follicles in the bursa of Fabricius as well as the circulating B-cells in the secondary lymphoid tissues such as GALT (gut-associated lymphoid tissue), CALT (conjuntiva), BALT (Bronchial) caecal tonsils, Harderian gland
Harderian gland
Harderian gland is a gland found within the eye's orbit which occurs in vertebrates that possess a nictitating membrane....
, etc. Acute disease and death is due to the necrotizing
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
effect of these viruses on the host tissue. If the bird survives and recovers from this phase of the disease, it remains immunocompromised which means it is more susceptible to other diseases.
Clinical signs
In the acute form birds are depressed, debilitated and dehydrated. They produce watery diarrhea and have swollen, blood-stained vent. It is common for the birds to be recumbent and show a ruffling of the feathers. Mortality rates vary with virulence of the strain involved, the challenge dose as well as the flock's ability to mount an effective immune response. Infection with less virulent strains may not show overt clinical signs but the birds may have fibrotic or cystic bursa of Fabricus that has atrophied prematurely (before six months of age) and may die of infections by agents that would not usually cause disease in immunocompetent birds.Diagnosis
A preliminary diagnosis can usually be made based on flock history, clinical signs and post-mortem (necropsy) examinations. However, definitive diagnosis can only be achieved by the specific detection and/or isolation and characterization of IBDV. ImmunofluorescenceImmunofluorescence
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...
or immunohistochemistry
Immunohistochemistry
Immunohistochemistry or IHC refers to the process of detecting antigens in cells of a tissue section by exploiting the principle of antibodies binding specifically to antigens in biological tissues. IHC takes its name from the roots "immuno," in reference to antibodies used in the procedure, and...
tests, based on anti-IBDV labelled antibodies, or in-situ hybridization, based on labelled complementary cDNA sequence probe, are useful for the specific detection of IBDV in infected tissues. RT-PCR (as mentioned above) was designed for the detection of IBDV genome, such as VP1 coding gene, with the possibility of PCR product sequences be determined for genetically comparing isolates and producing phylogenetic trees. Serological tests such as agar gel precipitation and ELISA, for detecting antibodies, are used for monitoring vaccine responses and might be an additional information of infection for unvaccinated flocks.
Necropsy examination will usually show changes in the bursa of Fabricius such as swelling, oedema, haemorrhage, the presence of a creamy transudate and eventually, atrophy. Pathological changes, especially haemorrhages, may also be seen in the muscle, intestines, kidney and spleen.
Treatment & Control
Vaccination in the face of outbreak will not be effective, therefore no treatment is available.Passive immunity protects against disease, as does previous infection with avirulent strains. In broiler farms, breeder flocks are immunised against IBD so that they would confer protective antibodies to their progenies, which would be slaughtered for consumption before their passive immunity wears out. The vaccines themselves can cause immunosuppression and damage to the bursa of fabricus. Appropriate hygiene measures are essential for prevention and control as the virus can survive for long periods in both housing and water.
See also
- Double-stranded RNA virusesDouble-stranded RNA virusesDouble-stranded RNA viruses are a diverse group of viruses that vary widely in host range , genome segment number , and virion organization...
- Animal virologyAnimal virologyThe study of animal viruses is important from a veterinary viewpoint and many of these viruses cause diseases that are economically devastating. Many animal viruses are also important from a human medical perspective...
External links
- Description, with photo of diseased organ
- IBD in Commercial Broilers
- Infectious Bursal Disease
- Infectious Bursal Disease, expert reviewed and published by WikiVetWikiVetWikiVet is a wiki of veterinary content, run using the MediaWiki software. The project is a collaborative initiative involving UK veterinary schools with external support...
at http://en.wikivet.net/Infectious_Bursal_Disease, accessed 13/09/2011