Epidemiology and Natural History of HIV

The human immunodeficiency virus (HIV) is a member of the genus Lentivirus, a subgroup of retrovirus (Retroviridae), that causes HIV infection, which, if untreated, results in acquired immunodeficiency syndrome (AIDS) and death. It was first described in 1981 during an epidemic of a previously unknown immunodeficiency syndrome in the US. The term HIV was accepted in 1986. HIV is thought to originate from simian immune deficiency virus (SIV). HIV-1 was discovered first, with the epidemic of AIDS in the US in 1981. In 1986, a related virus subsequently known as HIV-2, was identified in West Africa. The viruses differ in several aspects; HIV-1 is found worldwide, whereas HIV-2 is predominantly found in West Africa. HIV-1 is a more virulent and rapidly progressive virus; HIV-2 tends to be present in lower viral quantities and progresses more slowly. The number of people living with HIV (PLWH) rose from an estimated 9.0 million in 1990 to 36.9 million in 2014, due in part to a substantial improvement in survival rates as a result of effective anti-retroviral treatment. By 2014, annual new HIV infections had dropped to 2.0 million, down from 3.1 million in 2000, representing a decline of about 35%, although there remain an estimated 5600 people newly infected with HIV every day. It is estimated that without the global response that was mounted in 2000, notably the ‘Combatting of HIV/AIDS’ (the 6th Millennium Development Goal, which focused on halting and reversing trends for HIV by the end of 2015) there would have been six million new infections in 2013 alone. The main driver of progress has been widespread roll-out of antiretroviral treatment (ART) and behavioural change interventions, resulting in increased condom use, fewer multiple sexual partnerships, and delayed sexual debut. HIV-related deaths peaked in 2004–2005, and deaths fell by 24% between 2000 and 2014 from 1.2 million (0.98–1.6 million) in 2014 compared to 1.6 million (1.3–2.1 million) in 2000. The drop in AIDS-related mortality has been even steeper among children aged under fifteen years of age due to the enormous progress made with prevention of mother-to-child transmission (PMTCT).