HIV

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This article is about the virus. For the disease, see HIV/AIDS. For other uses, see HIV (disambiguation).

"AIDS virus" redirects here. For the computer virus, see AIDS (computer virus).

Human immunodeficiency virus
Scanning electron micrograph of HIV-1 (in green) budding from cultured lymphocyte. Multiple round bumps on cell surface represent sites of assembly and budding of virions.
Virus classification
Group:	Group VI (ssRNA-RT)
Order:	Unassigned
Family:	Retroviridae
Subfamily:	Orthoretrovirinae
Genus:	Lentivirus
Species
Human immunodeficiency virus 1 Human immunodeficiency virus 2

The human immunodeficiency virus (HIV) is a lentivirus (a subgroup of retrovirus) that causes the acquired immunodeficiency syndrome (AIDS),^[1][2] 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.^[3] Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells.
HIV infects vital cells in the human immune system such as helper T cells (specifically CD4⁺ T cells), macrophages, and dendritic cells.^[4] HIV infection leads to low levels of CD4⁺ T cells through a number of mechanisms, including apoptosis of uninfected bystander cells,^[5] direct viral killing of infected cells, and killing of infected CD4⁺ T cells by CD8 cytotoxic lymphocytes that recognize infected cells.^[6] When CD4⁺ T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections.