Avibirnavirus | |
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Infectious bursal disease virus particle | |
Virus classification
![]() | |
(unranked): | Virus |
Realm: | Riboviria |
Kingdom: | Orthornavirae |
Phylum: | incertae sedis |
Family: | Birnaviridae |
Genus: | Avibirnavirus |
Species [1] | |
Avibirnavirus is a genus of viruses in family Birnaviridae. [2] There is a single species in this genus: Infectious bursal disease virus, which infects chickens and other fowl. It causes severe inflammation of the bursa of Fabricius, and causes considerable morbidity and mortality. [3] [4]
Initially, the virus was discovered in 1957 in Gumboro, Delaware, United States. [5] [6] Later, the disease was termed Gumboro disease. Since its discovery, the virus has been found to have a worldwide distribution. [6]
Avibirnaviruses are non-enveloped, and their single shelled icosahedral capsid exhibits a T=13 symmetry. The diameter of the capsid is around 70 nm. [3] [4]
Genus | Structure | Symmetry | Capsid | Genomic arrangement | Genomic segmentation |
---|---|---|---|---|---|
Avibirnavirus | Icosahedral | T=13 | Non-enveloped | Linear | Segmented |
The double-stranded RNA genome of Avibirnaviruses is linear and segmented into two segments (A and B). [7] [8] The combined lengths of the two segments is around 6,000 nucleotides, almost entirely composed of reading-frames. The genome codes for 4-5 proteins depending on the strain. [3] [4] The high degree of antigenic variation is due to a combination of high mutation rate and inter-strain homologous recombination within a hypervariable region that is located in the vp2 gene. [6] [9]
At approximately 3,200 bp in length, segment A is the larger of the two segments. It contains two partially overlapping open reading frames (ORFs). [7] [8] The first ORF in segment A encodes viral protein 5 (VP5). [7] The second ORF in segment A encodes a polyprotein, the pVP2-VP4-VP3 precursor, which is cleaved into three proteins . [7] Segment B encodes a single viral protein, VP1. [7] [8]
Viral protein 1 is an RNA-dependent RNA polymerase, which cycles between the two segments and aids in the formation of ribonucleoprotein complexes with viral protein 3. [7]
Viral protein 2 is a major structural component of the virion. [7] The protein contains three domains: base, shell, and projection. [5] The projection domain consists of four loop structures that are exposed on the virion surface. [5] This protein is responsible for inducing a protective immune response, which neutralize monoclonal antibodies through binding to the project domain. [5] The viral protein in conjunction with VP5 acts as an apoptotic inducer, which causes affected cells to become cytotoxic. [9] Also, together with VP5, it inhibits cellular protein synthesis through activation of the protein kinase R pathway (PKR). [9] This activation leads to an increase in reactive oxygen species in the affected cells. [9]
Viral protein 3 is an immunogenic protein that interacts with VP1. [7] Its helps to regulate VP2 apoptosis by inhibiting phosphorylation of PKR and eukaryotic initiation factor 2 (eIF2). [9] Apoptotic regulation allows for the replication and release of the virus into other cells. [9]
Viral protein 4 is a serine protease, which catalyzes the hydrolysis of polyprotein pVP2-VP4-VP3 to release the viral proteins. [7] The serine protease that cleaves at ser-652 and lys-692. [7] This step is essential to replication due to release of the other proteins. [7] VP4 will additionally take over a glucocorticoid-induced leucine zipper protein (GILZ) that will allow for viral growth and block immune response of host cell. [7] [9]
Viral protein 5 is an inducer of apoptosis for DF-1 cells. [10] It relies on inhibiting the voltage-dependent anion channel 2 (VDCA2) located on the mitochondria. [10] The inhibition will be aided by VP2, which will close the channel allowing for proliferation of the virus in host cells. [9] [10] Also, VDCA2 will bind to RACK1 that will allow replication. [7]
The serotype and antigenic variations of the virus can only be distinguished between through virus-neutralization assays. [5] The project domains can be viewed to see the variation of the virus through amino acid substitutions. [5] The genome is typically highly conserved, however, the serotypes will vary the genome due to nucleotide changes. [8] There are two serotypes of avibirnavirus with one containing multiple classifications. [11] Serotype 1 is pathogenic to chickens especially at 3 to 6 weeks of age and seen to be more virulent in lighter breeds. [11] [9] This serotype contains three main classifications: classical virulent IBDV, very virulent IBDV, and variant IBDV. [11] [12] Classical virulent IBDV is the only serotype that has two subtypes: attenuated vaccine IBDV and classical virulent IBDV. [12] Although, these serotypes can have variance upon region. [5] Serotype 2 was identified in turkey. [5] This serotype has no pathogenic effect on chickens. [11]
Viral replication is cytoplasmic. Entry into the host cell is achieved by penetration into the host cell. The entry points in the host cell are through certain cell receptors. [11] One receptor that the virus will bind is surface immunoglobulin M, which specifically interacts with the light chains of the antibody. [9] Another receptor that can be bound is heat shock protein 90 (HSP90) on the surface of the DF-1 cell membrane. [9] Although, this receptor will bind either the virus or the VP2-viral sub particle. [9] Entry through the membrane has not been fully understood. [9] The penetration of the membrane is aided by the capsid PEP46. [9] The capid will have a peptide generated from the c-terminal of pVP2 that is released by VP4. [9] The peptide causes the membrane to become permeable by forming pores, which allow for PEP46 entry depending on calcium gradient. [9] If the inner calcium gradient is low, then it is thought to enter V-ATPase positive vesicles by endocytosis and uncoated for entry into the cytosol. [9] Also, it has been found VP2-α4β1 aids in spreading the virus in the cell as well through macropinocytosis. [9] This will allow for the virus to be moved to the early endosomes that is accomplished in the cell through Rab5. [9] Replication follows the double-stranded RNA virus replication model. Double-stranded rna virus transcription is the method of transcription. Young chickens and other fowl serve as the natural host. Transmission routes are contamination. [3] [4]
Genus | Host details | Tissue tropism | Entry details | Release details | Replication site | Assembly site | Transmission |
---|---|---|---|---|---|---|---|
Avibirnavirus | Birds | None | Cell receptor endocytosis | Budding | Cytoplasm | Cytoplasm | Contact |
Avibirnavirus | |
---|---|
![]() | |
Infectious bursal disease virus particle | |
Virus classification
![]() | |
(unranked): | Virus |
Realm: | Riboviria |
Kingdom: | Orthornavirae |
Phylum: | incertae sedis |
Family: | Birnaviridae |
Genus: | Avibirnavirus |
Species [1] | |
Avibirnavirus is a genus of viruses in family Birnaviridae. [2] There is a single species in this genus: Infectious bursal disease virus, which infects chickens and other fowl. It causes severe inflammation of the bursa of Fabricius, and causes considerable morbidity and mortality. [3] [4]
Initially, the virus was discovered in 1957 in Gumboro, Delaware, United States. [5] [6] Later, the disease was termed Gumboro disease. Since its discovery, the virus has been found to have a worldwide distribution. [6]
Avibirnaviruses are non-enveloped, and their single shelled icosahedral capsid exhibits a T=13 symmetry. The diameter of the capsid is around 70 nm. [3] [4]
Genus | Structure | Symmetry | Capsid | Genomic arrangement | Genomic segmentation |
---|---|---|---|---|---|
Avibirnavirus | Icosahedral | T=13 | Non-enveloped | Linear | Segmented |
The double-stranded RNA genome of Avibirnaviruses is linear and segmented into two segments (A and B). [7] [8] The combined lengths of the two segments is around 6,000 nucleotides, almost entirely composed of reading-frames. The genome codes for 4-5 proteins depending on the strain. [3] [4] The high degree of antigenic variation is due to a combination of high mutation rate and inter-strain homologous recombination within a hypervariable region that is located in the vp2 gene. [6] [9]
At approximately 3,200 bp in length, segment A is the larger of the two segments. It contains two partially overlapping open reading frames (ORFs). [7] [8] The first ORF in segment A encodes viral protein 5 (VP5). [7] The second ORF in segment A encodes a polyprotein, the pVP2-VP4-VP3 precursor, which is cleaved into three proteins . [7] Segment B encodes a single viral protein, VP1. [7] [8]
Viral protein 1 is an RNA-dependent RNA polymerase, which cycles between the two segments and aids in the formation of ribonucleoprotein complexes with viral protein 3. [7]
Viral protein 2 is a major structural component of the virion. [7] The protein contains three domains: base, shell, and projection. [5] The projection domain consists of four loop structures that are exposed on the virion surface. [5] This protein is responsible for inducing a protective immune response, which neutralize monoclonal antibodies through binding to the project domain. [5] The viral protein in conjunction with VP5 acts as an apoptotic inducer, which causes affected cells to become cytotoxic. [9] Also, together with VP5, it inhibits cellular protein synthesis through activation of the protein kinase R pathway (PKR). [9] This activation leads to an increase in reactive oxygen species in the affected cells. [9]
Viral protein 3 is an immunogenic protein that interacts with VP1. [7] Its helps to regulate VP2 apoptosis by inhibiting phosphorylation of PKR and eukaryotic initiation factor 2 (eIF2). [9] Apoptotic regulation allows for the replication and release of the virus into other cells. [9]
Viral protein 4 is a serine protease, which catalyzes the hydrolysis of polyprotein pVP2-VP4-VP3 to release the viral proteins. [7] The serine protease that cleaves at ser-652 and lys-692. [7] This step is essential to replication due to release of the other proteins. [7] VP4 will additionally take over a glucocorticoid-induced leucine zipper protein (GILZ) that will allow for viral growth and block immune response of host cell. [7] [9]
Viral protein 5 is an inducer of apoptosis for DF-1 cells. [10] It relies on inhibiting the voltage-dependent anion channel 2 (VDCA2) located on the mitochondria. [10] The inhibition will be aided by VP2, which will close the channel allowing for proliferation of the virus in host cells. [9] [10] Also, VDCA2 will bind to RACK1 that will allow replication. [7]
The serotype and antigenic variations of the virus can only be distinguished between through virus-neutralization assays. [5] The project domains can be viewed to see the variation of the virus through amino acid substitutions. [5] The genome is typically highly conserved, however, the serotypes will vary the genome due to nucleotide changes. [8] There are two serotypes of avibirnavirus with one containing multiple classifications. [11] Serotype 1 is pathogenic to chickens especially at 3 to 6 weeks of age and seen to be more virulent in lighter breeds. [11] [9] This serotype contains three main classifications: classical virulent IBDV, very virulent IBDV, and variant IBDV. [11] [12] Classical virulent IBDV is the only serotype that has two subtypes: attenuated vaccine IBDV and classical virulent IBDV. [12] Although, these serotypes can have variance upon region. [5] Serotype 2 was identified in turkey. [5] This serotype has no pathogenic effect on chickens. [11]
Viral replication is cytoplasmic. Entry into the host cell is achieved by penetration into the host cell. The entry points in the host cell are through certain cell receptors. [11] One receptor that the virus will bind is surface immunoglobulin M, which specifically interacts with the light chains of the antibody. [9] Another receptor that can be bound is heat shock protein 90 (HSP90) on the surface of the DF-1 cell membrane. [9] Although, this receptor will bind either the virus or the VP2-viral sub particle. [9] Entry through the membrane has not been fully understood. [9] The penetration of the membrane is aided by the capsid PEP46. [9] The capid will have a peptide generated from the c-terminal of pVP2 that is released by VP4. [9] The peptide causes the membrane to become permeable by forming pores, which allow for PEP46 entry depending on calcium gradient. [9] If the inner calcium gradient is low, then it is thought to enter V-ATPase positive vesicles by endocytosis and uncoated for entry into the cytosol. [9] Also, it has been found VP2-α4β1 aids in spreading the virus in the cell as well through macropinocytosis. [9] This will allow for the virus to be moved to the early endosomes that is accomplished in the cell through Rab5. [9] Replication follows the double-stranded RNA virus replication model. Double-stranded rna virus transcription is the method of transcription. Young chickens and other fowl serve as the natural host. Transmission routes are contamination. [3] [4]
Genus | Host details | Tissue tropism | Entry details | Release details | Replication site | Assembly site | Transmission |
---|---|---|---|---|---|---|---|
Avibirnavirus | Birds | None | Cell receptor endocytosis | Budding | Cytoplasm | Cytoplasm | Contact |