Classifications

Classification

HIV is a member of the genus Lentivirus, part of the family of Retroviridae. Lentiviruses have many common morphologies and biological properties. Many species are infected by lentiviruses, which are characteristically responsible for long-duration illnesses with a long incubation period. Lentiviruses are transmitted as single-stranded, positive-sense, enveloped RNA viruses. Upon entry of the target cell, the viral RNA genome is converted to double-stranded DNA by a virally encoded reverse transcriptase that is present in the virus particle. This viral DNA is then integrated into the cellular DNA by a virally encoded integrase, along with host cellular co-factors, so that the genome can be transcribed. After the virus has infected the cell, two pathways are possible: either the virus becomes latent and the infected cell continues to function or the virus becomes active and replicates, and a large number of virus particles that can then infect other cells are liberated.
There are two species of HIV known to exist: HIV-1 and HIV-2. HIV-1 is the virus that was initially discovered and termed LAV. It is more virulent, more infective, and is the cause of the majority of HIV infections globally. The lower infectivity of HIV-2 compared to HIV-1 implies that fewer of those exposed to HIV-2 will be infected per exposure. Because of its relatively poor capacity for transmission, HIV-2 is largely confined to West Africa.

Comparison of HIV species
Species Virulence Infectivity Prevalence Inferred origin
HIV-1> High High Global Common Chimpanzee
HIV-2> Lower Low West Africa Sooty Mangabey