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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
#*[[Sheep Pulmonary Adenomatosis]]
#Avian Type C retrovirus
#*[[Avian Leukosis Virus]]
#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===
===Retroviruses===