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==Agent==
 
==Agent==
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FIV is a member of the lentivirus genus of the Retroviridae family. Retrovirus virions are are sensitive to heat, lipid solvents, and detergents but are relatively resistant to damage caused by ultraviolet light<sup>viro</sup>. The Retroviridae are enveloped viruses which contain a single-stranded RNA genome within an icosahedral nucleocapsid. Glycoprotein surface spikes are located on the envelope. Unusually, Retroviruses have a diplod genome: two identical copies of their positive-sense ssRNA are found on the virion<sup>viro</sup>. During viral replication, reverse transcriptase converts the ssRNA genome to ssDNA. This process is inherently error-prone, and the high rate of mutation gives rise to a wide genetic diversity of virus<sup>viro</sup>. A dsDNA can then be made from the ssDNA template. This provirus DNA then becomes integrated into the host genome by the actions of the viral enzyme integrase, and remains latent until transcription is initiated by the host cell machinery<sup>viro</sup>. Proviral DNA then serves as a template for the production of progeny ssRNA genomes and messenger RNA. Once the proviral DNA has been transcribe and translated, the virions assemble and are release by budding through the host cell membrane. This does not always cause lysis<sup>viro</sup>.
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FIV is a member of the lentivirus genus of the Retroviridae family. Retrovirus virions are are sensitive to heat, lipid solvents, and detergents but are relatively resistant to damage caused by ultraviolet light<sup>1</sup>. The Retroviridae are enveloped viruses which contain a single-stranded RNA genome within an icosahedral nucleocapsid. Glycoprotein surface spikes are located on the envelope. Unusually, Retroviruses have a diplod genome: two identical copies of their positive-sense ssRNA are found on the virion<sup>1</sup>. During viral replication, reverse transcriptase converts the ssRNA genome to ssDNA. This process is inherently error-prone, and the high rate of mutation gives rise to a wide genetic diversity of virus<sup>1</sup>. A dsDNA can then be made from the ssDNA template. This provirus DNA then becomes integrated into the host genome by the actions of the viral enzyme integrase, and remains latent until transcription is initiated by the host cell machinery<sup>1</sup>. Proviral DNA then serves as a template for the production of progeny ssRNA genomes and messenger RNA. Once the proviral DNA has been transcribe and translated, the virions assemble and are release by budding through the host cell membrane. This does not always cause lysis<sup>1</sup>.
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Many Retrovirus genomes contain oncogenes which may be expressed when integrated to the host genomes. However, oncogenes are not a requirement for tumour induction, and some Retroviruses can cause tumours without carrying oncogenes. The Retroviral genome has four coding regions. The "gag" region codes for the matrix protein, nucleoprotein and capsid, and "pro" encodes a protease<sup>viro</sup>. Reverse transcriptase is coded by the "pol" region, whereas "env" gives rise to the envelope and receptor binding. An additional, specific cellular transporter RNA is required for replication and present within the virion.
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Many Retrovirus genomes contain oncogenes which may be expressed when integrated to the host genomes. However, oncogenes are not a requirement for tumour induction, and some Retroviruses can cause tumours without carrying oncogenes. The Retroviral genome has four coding regions. The "gag" region codes for the matrix protein, nucleoprotein and capsid, and "pro" encodes a protease<sup>1</sup>. Reverse transcriptase is coded by the "pol" region, whereas "env" gives rise to the envelope and receptor binding. An additional, specific cellular transporter RNA is required for replication and present within the virion.
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FIV was first discovered in a cat rescue facility in the
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United States where some of the cats had been showing
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similar clinical signs to people with acquired immunodeficiency
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syndrome (AIDS). The virus has subsequently been
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found to be very similar to the retrovirus human immunodeficiency
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virus (HIV). It is now known from serological
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data that FIV has been in the cat population since at least
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the late 1960s. The prevalence of infection varies hugely
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from country to country. In the UK, around 7 per cent of
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the healthy and 19 per cent of the sick cat population are
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infected with the virus (Hosie and others 1989).
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Electron micrograph image
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of FIV particles (arrows)
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released from an adjacent
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lymphocyte (1).
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Original magnification x 70 000
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Although there are many similarities between HIV and
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FIV, the viruses are species specific and there is no
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zoonotic risk to people in contact with an FIV-positive cat.
    
==Transmission and Epidemiology==
 
==Transmission and Epidemiology==
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