Human Immunodeficiency Virus Types 1 and 2: Global History, Occurrence, and Spread

Human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) are retroviruses that attack and destroy cells essential to the regulation of immune function, primarily the CD4+ subset of lymphocytes. Globally, HIV-1 surpasses HIV-2 in frequency and severity. In the absence of treatment, the deterioration of cell-mediated immunity eventually becomes profound enough to produce fatal acquired immunodeficiency syndrome (AIDS) characterized by a spectrum of opportunistic infections, neoplasms, and other end-organ pathology. Following the recognition of AIDS in 1981, HIV-1 infection soon reached pandemic proportions. By 2022, some 40 million people with HIV infection had died, and an estimated 39 million were living with HIV-1 infection. The affected populations vary greatly by geographic, socioeconomic, and behavioral factors. Infection is spread by several routes, with sexual transmission being the most important. AIDS was originally discovered in men who have sex with men, who remain at high risk. In sub-Saharan Africa and Asia, heterosexual transmission accounts for the brunt of the AIDS epidemic. In Eastern Europe, Southeast Asia, and many urban areas elsewhere, persons who inject drugs represent another subpopulation at especially high risk. In poorly resourced locations, contamination of blood products and reused medical equipment are significant sources of infection, and perinatal transmission continues to occur where prenatal diagnosis and treatment are lacking. In contrast, under the most favorable circumstances, multiple antiretroviral agents combined in increasingly simple, well-tolerated regimens have proved capable of suppressing viremia to undetectable levels, essentially halting both transmission and disease progression. As a result, public health authorities have optimistically aspired to “ending AIDS” globally by 2030 and have generated concrete plans to achieve that goal.