 HIV, the human immunodeficiency virus HIV is a lentivirus, a subgroup of retrovirus that causes HIV infection and over time acquired immunodeficiency syndrome AIDS. AIDS is a condition in humans in which progressive failure of the immune system allows life threatening opportunistic infections and cancers to thrive. Treatment, average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype. 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 during pregnancy, during childbirth by exposure to her blood or vaginal fluid, and through 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 plus T cells macrophages, and dendritic cells. HIV infection leads to low levels of CD4 plus T cells through a number of mechanisms, including pyroptosis of abortively infected T cells, apoptosis of un-infected by standard cells, direct viral killing of infected cells, and killing of infected CD4 plus T cells by CD8 plus cytotoxic lymphocytes that recognize infected cells. When CD4 plus 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.