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What are the most significant factors that contributed to HIV/AIDS becoming a global problem?

The first people to become infected with the HIV-1(M) virus, which causes 97% of HIV infections worldwide, were probably bush meat traders in the Democratic Republic of Congo (DRC) [1].  When the chimpanzee species Pan troglodyte troglodyte was killed, eaten, or blood got into cuts or wounds on the hunters’ skin, a hybrid form of the Simian Immune Deficiency Virus (SIVcpz) crossed from chimpanzee to human host, where it mutated into what we now know as HIV [2].  It is thought that by the 1960s up to 2,000 people in West Africa may have been infected by HIV-1, but the first signs of an epidemic occurred in the 1970s after an infected individual travelled from Cameroon, down river to Kinshasa, DRC, where the virus was able to spread quickly by a wide urban sexual network [3].  This scenario appears to provide early evidence of two of the main factors influencing the rapid spread of HIV – human mobility and human sexual behaviours.

The virus is thought to have spread quickly in parts of Africa due to widespread labour migration, a high ratio of men in urban populations combined with a low status of women, leading to a thriving sex trade, as well as lack of circumcision in men and high rates of sexually transmitted diseases, which provide a vulnerable environment for the virus to take hold [3].

HIV belongs to a subgroup of Retroviruses, named Lentiviruses, meaning slow viruses.  There is a significant period of time between the time of infection with a Lentivirus, and the beginning of symptoms [4].  This aspect of HIV allows it to spread unwittingly between people who may remain unaware of their infection for up to several years [5].

The spread of HIV followed human movements, with the highest prevalence rate of HIV in Africa in 1988 being found on the main highway linking Tanzania and Zambia, and by the late 1980s most of Southern Africa was significantly afflicted [3].  It is thought that the first case of HIV in South Africa was a white American air steward, who died in 1982 from Pneumocystic Pneumonia in 1982, and in 1983 16% of tested gay men in Johannesburg were HIV positive [3].  It was around this time that conditions now known as AIDS-defining illnesses began to appear in gay men in the USA, as well as a small number of heterosexual men and women, many of whom had a history of intravenous drug use [6].

HIV positive people may remain unaware of their infection for years before developing symptoms, due to the long latency period of the virus.  This reduces the likelihood of people altering high risk behaviours before diagnosis.  Such behaviours may include multiple sexual partners and unsafe IV drug use (eg sharing needles) .  Prior to identification of the virus and without implementation of protective measures (now routinely employed in first world donor blood), it is also able to transmit between humans via blood transfusions [7].  These factors combined with the changing pattern of domestic and international travel which occurred around the same time as the virus crossed over to human hosts, allowed it to spread rapidly across human populations around the globe.