The human immunodeficiency virus, the virus that causes acquired immunodeficiency syndrome (AIDS), might have been in humans for much longer than thought.
The origin of this devastating virus has puzzled scientists ever since it first came to light in the 1980s.
Among popular belief is that the virus originated in Central Africa from chimpanzees infected with simian immunodeficiency virus (SIV), as part of a research experiment.
The first case of AIDS was recorded in the United States in the early 1980s after a number of gay men in the cities of New York and California suddenly developed rare opportunistic infections and cancers resistant to treatment.
Then the new illness had no name yet, but it soon became apparent that all those men were suffering from a common syndrome. Soon thereafter HIV (the Human Immunodeficiency Virus) was discovered. While some scientists were initially sceptical about the connection (and indeed some remain so today), it is now generally believed that HIV causes AIDS. There are many theories on this subject, but during my research I bumped into three very interesting theories on how SIV became HIV in humans.
The first theory is the Hunter Theory. According to this theory, SIV was transferred when humans killed and ate chimps or their blood got contaminated when they sustained cuts or wounds during hunting.
Normally the hunter's body would resist SIV infection, but in some occasions the virus adapted within its human host and became HIV-1.
The fact that there were several different early strains of HIV, each with a slightly different genetic make-up, supports the theory that every time the virus passed from a chimpanzee to a human being, it mutated and thus produced a slightly different strain.
An article published in The Lancet medical journal in 2004 shows how retroviral transfer from primates to hunters could still be occurring today.
Of the 1 099 individuals used in a test carried out in Cameroon, 10 were infected with SFV (Simian Foamy Virus), an illness which, like SIV, was previously thought only to infect primates.
All these infections were believed to have been acquired through the butchering and consumption of monkey and ape meat.
Such discoveries led to calls for an outright ban on bush meat consumption in order to prevent simian viruses from spreading to humans.
Oral Polio Vaccine
The second theory is the Oral Polio Vaccine (OPV). This controversial theory contends that HIV was transferred via medical interventions. One particularly well-publicised idea is that polio vaccines played a role in the transfer of the virus.
In his book, ‘The River’, journalist Edward Hooper suggests that HIV can be traced to the testing of an oral polio vaccine called Chat, given to about a million people in the Belgian Congo, Rwanda and Burundi in the late 1950s.
To reproduce, polio virus needs living tissue, and Hooper believes that Chat was grown in kidney cells taken from local chimps infected with SIV.
This, he claims, would result in the contamination of the vaccine with chimps’ SIV, and a large number of people subsequently becoming infected with HIV-1.
Many people have contested Hooper's submission by insisting that local chimps were not infected with a virus strain that is closely linked to HIV.
Furthermore, the oral administration of the vaccine would seem insufficient to cause infection in most people (SIV/HIV needs to get directly into the bloodstream to cause infection, as the lining of the mouth and throat generally act as good barriers to the virus).
In February 2000, the Wistar Institute in Philadelphia (one of the original manufacturers of the Chat vaccine) announced that it had discovered in its stores a phial of polio vaccine that had been used as part of the programme.
The vaccine was subsequently analysed and results announced in April 2001 showed no trace of either HIV or chimpanzee SIV.
A second analysis confirmed that only macaque monkey kidney cells, which cannot be infected with SIV or HIV, were used to make Chat.
That this was just one out of many phials means the OPV theory remains unproven.
Contaminated Needle Theory
The third theory is called the Contaminated Needle Theory and is an extension of the 'hunter' theory. In the 1950s, the use of disposable plastic syringes became commonplace around the world as a cheap, sterile way to administer medicines. However, to African healthcare professionals working on inoculation and other programmes, the huge quantities of syringes and needles needed would have been very costly. Therefore, one needle was likely to be used to inject multiple patients before it could be sterilised.
This would have rapidly transferred any virus (within a hunter's blood for example) from one person to another, creating fertile ground for the virus to mutate and replicate in each new host, even if the SIV within the first person infected had not yet converted to HIV.