HIV

The human immunodeficiency virus (HIV) is a lentivirus (a subgroup of retrovirus) that causes HIV infection and over time acquired immunodeficiency syndrome (AIDS).^[1][2] AIDS is a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancersto thrive. Without treatment, average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype.^[3] In most cases, HIV is a sexually transmitted infection and occurs by contact with or transfer of blood, pre-ejaculate, semen, and vaginal fluids. Non-sexual transmission can occur from an infected mother to her infant through breast milk.^[4][5][6] An HIV-positive mother can transmit HIV to her baby both during pregnancy and childbirth due to exposure to her blood or vaginal fluid.^[7]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.^[8] HIV infection leads to low levels of CD4⁺ T cells through a number of mechanisms, including pyroptosis of abortively infected T cells,^[9] apoptosis of uninfected bystander cells,^[10] direct viral killing of infected cells, and killing of infected CD4⁺ T cells by CD8⁺ cytotoxic lymphocytes that recognize infected cells.^[11] 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, leading to the development of AIDS.

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