AIDS is a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive.
Without treatment, average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype.
Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk.
HIV infects vital cells in the human immune system such as helper T cells (specifically CD4 Lentiviruses have many morphologies and biological properties in common.
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 into the target cell, the viral RNA genome is converted (reverse transcribed) into double-stranded DNA by a virally encoded reverse transcriptase that is transported along with the viral genome in the virus particle.
The resulting viral DNA is then imported into the cell nucleus and integrated into the cellular DNA by a virally encoded integrase and host co-factors.
Once integrated, the virus may become latent, allowing the virus and its host cell to avoid detection by the immune system.
Alternatively, the virus may be transcribed, producing new RNA genomes and viral proteins that are packaged and released from the cell as new virus particles that begin the replication cycle anew.
Two types of HIV have been characterized: HIV-1 and HIV-2.
HIV-1 is the virus that was initially discovered and termed both LAV and HTLV-III.