Saturday, 15 May 2010

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From monkey to man?

The most popular theory about the origin of the HIV virus traces its origin to various simian breeds in the African continent from where colonialism facilitated its entry to other parts of the world

Doctors in Los Angeles in 1981 were the first to recognise AIDS as a new disease. What alerted them was the appearance between 1979 and 1981 of many cases of rare types of pneumonia, cancer and other illnesses in a number of gay men (men who have sex with men, or MSM). These were conditions not usually found in people with healthy immune systems; moreover their bodies could not overcome the infections.

In 1982 public health officials began to use the term ‘acquired immunodeficiency syndrome’, or AIDS, to describe the occurrences of opportunistic infections (infections usually not seen in people with a healthy immune system but which use the “opportunity” given a weak immune system), Kaposi's sarcoma (a kind of cancer), and Pneumocystis carinii pneumonia (a kind of pneumonia caused by a yeast-like fungus that is relatively rare in people with normal immune systems but common in people with weak immune systems) in previously healthy men.

In 1983, a team of French scientists led by Luc Montagnier at the Pasteur Institute in Paris claimed credit for discovering the lymphadenopathy-associated virus, or LAV. In 1984, a US team led by Robert Gallo at the National Cancer Institute claimed to have discovered the same virus that they named human T lymphotropic virus type III (HTLV-III). After a prolonged and heated dispute, they agreed in 1987 to share the credit and the name was changed to HIV (Human Immunodeficiency Virus).

Over the years, several theories have been proposed to explain the origin of the virus. It is now generally accepted that HIV is a descendant of a Simian Immunodeficiency Virus (SIV) since certain strains of SIV bear a very close resemblance to HIV-1 and HIV-2, the two types of HIV. While HIV-2 corresponds to a strain of the SIV found in the sooty mangabey, a monkey indigenous to western Africa, HIV-1 corresponds to a strain found in chimpanzees.

There are several theories put forward by those who have attempted to discover not just the origin of the virus, but also the factors responsible for its early spread. The most commonly accepted theory is that of the ‘hunter’. This theory proposes that SIV was transferred to humans as a result of chimpanzees being killed and eaten or their blood getting into cuts or wounds on the hunter. It is possible that in some cases SIV adapted itself within its new human host and become HIV-1. The fact that there were several different early strains of HIV, each with a slightly different genetic make-up, would support this theory: every time it passed from a chimpanzee to a man, it would have developed in a slightly different way within his body, and thus produced a slightly different strain.

In the 1950s, the increase in medical interventions, and especially the use of needles and syringes for immunisation programmes and blood tests, would have rapidly spread blood-borne viruses. It is known that syringes and needles were reused to inject multiple patients without any sterilisation in between. This would have created huge potential for the virus to mutate and replicate in each new individual it entered, even if the SIV within the original person infected had not yet converted to HIV.

The Colonialism theory, proposed in 2000 by Jim Moore, a specialist in primate behaviour, suggests that the poor sanitation, scarce food and unhygienic conditions in labour camps into which many Africans were forced by their colonial masters in the late 19th and early 20th centuries, led to weakened immune systems, creating a potential for SIV to infiltrate and convert to HIV.

It is possible that chimpanzees with SIV were eaten by the starving workers. Possibilities for onward transmission according to this theory include mass inoculation programmes with unsterile needles against diseases such as smallpox and the employment of prostitutes at the camps to keep workers happy. The fact that the labour camps were set up around the early part of the 20th century - the time that HIV was first believed to have passed into humans – supports the colonialism theory.

There are other theories which have been discredited due to lack of supporting evidence. These include the conspiracy theory: that the virus is manmade as part of a biological warfare programme. The oral polio vaccine theory proposes that blood and kidney tissue of 300 chimpanzees were used in an experimental polio vaccine campaign that went awry.

In January 2000, the results of a new study presented at the 7th Conference on Retroviruses and Opportunistic Infections, suggested that the first case of HIV-1 infection occurred around 1930 in West Africa. The study was carried out by Dr Bette Korber of the Los Alamos National Laboratory. The estimate of 1930 (which has a 15 year margin of error) was based on a complex computer model of HIV's evolution.


  1. Gray R H, Wawer M J, Brookmeyer R, et al: ‘Probability of HIV-1 transmission per coital act in monogamous, heterosexual, HIV-1-discordant couples in Rakai, Uganda.’ The Lancet 2001; 357: 1149-1153.
  2. Mastro T D, Kitayaport D: ‘HIV type 1 transmission probabilities: estimates from epidemiological studies’, AIDS Research & Human Retroviruses, 1998 (suppl 3): S223-S227.
  3. Varghese B, Maher J E, Peterman T A, Mranson B M, Steketee R W: ‘Reducing the risk of sexual HIV transmission: quantifying the per-act risk for HIV on the basis of choice of partner, sex act, and condom use’, Sexually Transmitted Diseases, 2002; 29: 38-43.
  4. Vittinghoff E, Douglas J, Judson F, McKirnan D, MacQueen K, Buchbinder S P: ‘Per-contact risk of human immunodeficiency virus transmission between male sexual partners’, American Journal of Epidemiology, 1999; 150: 306-311.

InfoChange News & Features, March 2008

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