INTRODUCTION
Retroviridae are enveloped, single-stranded non-segmented RNA viruses. Their replication strategy is characterized by reverse transcription of their RNA into double-stranded DNA, which is integrated into the host chromosomal DNA.
Retroviruses are classified into seven genera. The alpharetroviruses, betaretroviruses and gammaretroviruses are grouped as simple retroviruses, the genome of which encodes only for the Gag, Pol, Pro and Env proteins. The deltaretroviruses, epsilonretroviruses, lentiviruses and spumaviruses are more complex retroviruses, with a genome encoding an additional array of small regulatory proteins.The integrated viral DNA or provirus contributes to the ability of the retroviruses to maintain persistent infection, and enter the germ line (cells at the origin of, and including, the gametes), allowing vertical transmission. This integration into the germ line results in endogenous retroviruses. These retrovirus-like DNA sequences, present in most eukaryote cells, are not associated with virus production or disease. Exogenous retroviruses are infectious and commonly associated with disease, including the development of malignant tumours, wasting diseases, neurologic disorders and immunodeficiencies.