Origin and Evolution of Human Immunodeficiency Viruses

Abstract

Human immunodeficiency virus (HIV) is a retrovirus that is classified in the genus Lentivirus. Lentiviruses are uniquely distinguished from other retroviruses by having a long latency period between infection and the manifestation of symptoms, a characteristic that confers the genus its Latin etymology (lentus being the adjective for “slow”) [1]. Moreover, lentiviruses are transmitted between hosts without the need for an intermediate vector, infect a broad range of mammalian hosts, and have a worldwide distribution. There are presently seven recognized major lentivirus lineages reflecting the known mammalian host range (lagomorph, equine, small ruminant, bovine, feline, prosimian, and simian [2, 3]). The virus genomes representing these lineages share a common genomic structure comprising three major genes (gag, pol, and env) and two regulatory genes (tat and rev); however, there are also a number of accessory genes that vary in number, type and relative location (Fig. 23.1).