The origin of the Human Immunodeficiency Virus (HIV) has been debated since the virus was identified in the 1980s by researchers and scientists. Now, we have a lot of evidence on how, when and where HIV first began to cause illness in humans.
HIV is a type of lentivirus, which means it attacks the immune system. In a similar way, the Simian Immunodeficiency Virus (SIV) attacks the immune system of apes and monkeys. HIV crossed from chimps to humans in the 1920s in what is now the Democratic Republic of Cango. This was probably as a result of chimps carrying SIV being hunted and eaten by people living in the area.
Researchers found that HIV is related to SIV and there are many similarities between the two viruses, HIV-1 is closely related to strains of SIV found in chimpanzee s, and HIV-2 is closely related to strains of SIV found in sooty mangabeys. In 1999, researchers found a strain of SIV (called SIVcpz) in a chimpanzee that was almost identical to HIV in humans. The researcher who discovered this connection concluded that it proved that chimpanzees were the source of HIV-1 and that the virus had at some point crossed species from chimps to humans.
The most commonly accepted theory is of the "hunter". In this scenario, SIVcpz was transferred to humans as a result of chimps being killed and eaten, or their blood getting into cuts or wounds on people in the course of hunting. Normally, the hunter's body would have fought off SIV, but on a few occasions the virus adapted itself within its new human host and became HIV-1.
Some studies of the earliest samples of HIV provide clues about when it first appeared in humans and how it evolved. The first verified case of HIV is from a blood sample taken in 1959 from a man. The sample was retrospectively analysed and HIV detected. The infections, now known to be Aids-defining, suggest that HIV was the cause, but this is the earliest incident where blood sample can verify infection.
Using the earliest known sample of HIV, scientists have been able to discover where HIV started. Their studies concluded that the first transmission of SIV to HIV in humans took place around 1920 in Kinshasa in the Democratic Republic of Congo.
The area around Kinshasa is full of transport links, such as roads, railways and rivers. The areas had a growing sex trade around the time that HIV began to spread. The high population of migrants and sex trade might explain how HIV spread along these infrastructure routes.
People sometimes say that HIV started in the 1989s in the United States of America (USA), but in fact, this was just when people first became aware of HIV and it was officially recognized as a new health condition. In 1981, a few of rare diseases were being reported among gay men in New York and California, such as Kaposi's Sarcoma (rare cancer) and a lung infection called PCP. No one knew why these cancers and opportunistic infections were spreading, but they concluded that there must be an infectious "disease" causing them.
At first, the disease was called all sorts of names relating to the word 'gay'. It wasn't until mid-1982 that scientists realised the "disease" was also spreading among other populations such as heroin users. By the September that year, the "disease" was finally named Aids.
