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Feline Immunodeficiency Virus (view source)
Revision as of 11:56, 27 August 2010
, 11:56, 27 August 2010→Agent
FIV is prevalent in cat populations throughout the world and is an important cause of feline disease. FIV belongs to the lentivirus family of the retrovirus group.
FIV is prevalent in cat populations throughout the world and is an important cause of feline disease. FIV belongs to the lentivirus family of the retrovirus group.
* These RNA viruses are enveloped, single-stranded RNA with an icosahedral nucleocapsid.
* The envelope has glycoprotein surface spikes (see Fig. 15.1). Retroviruses are unique among viruses in that they bring two identical copies of their genome in virions (are diploid).
* The ssRNA is converted to ssDNA by the enzyme reverse transcriptase. From the ssDNA, dsDNA (called provirus DNA) is made, which is then integrated into the host chromosome. The provirus dsDNA then serves as a template for the production of mRNA and progeny ssRNA genomes.
* The conversion of ssRNA to ssDNA, mediated by the viral enzyme reverse transcriptase, results in a dsDNA molecule longer than that of the original genome. This dsDNA migrates to the nucleus where it is ultimately integrated into the host chromosome by the viral enzyme integrase.
* Once integrated into the host genome, the viral dsDNA is referred to as a provirus. The provirus remains latent until "triggered" into transcription of mRNA by host cell machinery.
* Viral mRNA transcription of the provirus is mediated by cellular RNA polymerase II.
* The new virions are released by budding, which does not always result in cell lysis.
* There is a high mutation rate, as reverse transcription is an error-prone process. Thus, retroviruses usually present a high genetic diversity.
* Many retroviruses carry oncogenes (e.g., Rous sarcoma virus in chickens), while others do not (e.g., human T-cell lymphotrophic virus). However, some retroviruses may cause tumors without carrying oncogenes.
* All retroviral genomes consist of two molecules of ssRNA, (+)sense, have 5' cap and 3' poly-(A) (equivalent to mRNA) and four characteristic coding regions (gag-pro-pol-env). Gag (group specific antigen: matrix protein, nucleoprotein, capsid) genes; pro (protease) gene; pol (reverse transcriptase and RNase-H); and env (envelope, receptor binding) genes (see Fig.15.2). These vary in size from ~8-11 kb. They are the only viruses that are truly diploid. Additionally, there is a specific type of cellular transporter RNA (tRNA) (usually trp, pro or lys) - required for replication that is present in the virion.
* The virions are sensitive to heat, lipid solvents, and detergents but are relatively resistant to ultraviolet light damage.
==Transmission and Epidemiology==
==Transmission and Epidemiology==