Difference between revisions of "Retroviridae"
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=Introduction= | =Introduction= | ||
| − | Retroviruses are persistent, non-cytopathic, systemic viruses that give rise to secondary disease, such as tumors, immune-complex disease, or immunosuppression | + | Retroviruses are persistent, non-cytopathic, systemic viruses that give rise to secondary disease, such as tumors, immune-complex disease, or immunosuppression. |
=Morphology= | =Morphology= | ||
Revision as of 16:29, 18 October 2008
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This article is still under construction. |
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Introduction
Retroviruses are persistent, non-cytopathic, systemic viruses that give rise to secondary disease, such as tumors, immune-complex disease, or immunosuppression.
Morphology
- Fragile, enveloped RNA viruses with roughly spherical spike proteins
- Genome has 3 genes:
- gag: group-specific antigen coding gene, encodes capsid proteins
- pol: encodes reverse transcriptase (RT) and integrase
- env: encodes envelope spikes, and can be used in diagnosis and subunit vaccines
- Both ends of genome show a promoter (LTR: long terminal repeat)
Virulence and Pathogenesis
- Replication involves integrating into the host cell genome:
- Uncoating to release RNA and RT
- +RNA transcribed to -DNA by RT
- -DNA becomes circular dsDNA and is integrated into host chromosome by integrase
- DNA codes for viral proteins using cellular organelles and enzymes
- Because of this technique, virus replication is much slower, and retroviruses can remain latent
- Tumor production takes 2 forms:
- Viruses can carry oncogenes within their genome --> tumor production occurs quickly
- Insertion of the viral LTR switches on proto-oncogenes in the host cell genome --> tumor production can take years
Types and Subtypes
7 Genera, including these of veterinary relevance:
- Mammalian Type C retrovirus
- Feline Leukemia Virus (FeLV
- Feline sarcoma virus (rare)
- Porcine type C oncovirus (rare)
- Mammalian Type D retrovirus
- Avian Type C retrovirus
- Spumavirus
- Feline and bovine syncitial viruses (common, nonpathogenic)
- BLV-HTLV retroviruses
- Bovine Leukosis Virus
- Lentiviruses
- Feline Immunodeficiency Virus (FIV)
- Bovine Immunodeficiency Virus
- Visna-Maedi Virus of Sheep
- Caprine Arthrirtis Encephalitis Virus
- Equine Infectious Anemia
- Jembrana of Bali cattle
- Human Immunodeficiency Virus (HIV)
Antigenicity
- Group-specific antigens (gag's) are shared by all isolates of each virus
- This can be exploited by diagnostic tests
- Lentiviruses show variation by mutation, making vaccination difficult
Retroviruses
- SPA in sheep
- FeLV in skin infections
Lentiviruses
- Maedi visna virus causes respiratory disease and arthritis
- Caprine arthritis-encephalitis in goat pneumonia and arthritis
- FIV in skin infections