When? Aids Spread

During the last few years it has become possible not only to determine whether HIV is present in a blood or plasma sample, but also to determine the particular subtype of the virus. Studying the subtype of virus of some of the earliest known instances of HIV infection can help to provide clues about the time it first appeared in humans and its subsequent evolution.

Three of the earliest known instances of HIV infection are as follows:

1. A plasma sample taken in 1959 from an adult male living in what is now the Democratic Republic of Congo.

2. HIV found in tissue samples from an American teenager who died in St. Louis in 1969.

3. HIV found in tissue samples from a Norwegian sailor who died around 1976.

A 1998 analysis of the plasma sample from 1959 has suggested7 that HIV-1 was introduced into humans around the 1940s or the early 1950s; much earlier than previously thought. Other scientists have dated the sample to an even earlier period - perhaps as far back as the end of the 19th century.

In January 2000 however, 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 does have a 15 year margin of error) was based on a complicated computer model of HIV's evolution. If accurate, it means that HIV was in existence before many scenarios (such as the OPV and conspiracy theories) suggest.

What about HIV-2? When did that get passed to humans?

Until recently, the origins of the HIV-2 virus had remained relatively unexplored. HIV-2 is thought to come from the SIV in Sooty Mangabeys rather than chimpanzees, but the crossover to humans is believed to have happened in a similar way (i.e. through the butchering and consumption of monkey meat). It is far rarer, significantly less infectious and progresses more slowly to AIDS than HIV-1. As a result, it infects far fewer people, and is mainly confined to a few countries in West Africa.

In May 2003, a group of Belgian researchers lead by Dr. Anne-Mieke Vandamme, published a report8 in Proceedings of the National Academy of Science. By analysing samples of the two different subtypes of HIV-2 (A and B) taken from infected individuals and SIV samples taken from sooty mangabeys, Dr Vannedamme concluded that subtype A had passed into humans around 1940 and subtype B in 1945 (plus or minus 16 years or so). Her team of researchers also discovered that the virus had originated in Guinea-Bissau and that its spread was most likely precipitated by the independence war that took place in the country between 1963 and 1974 (Guinea-Bissau is a former Portuguese colony). Her theory was backed up by the fact that the first European cases of HIV-2 were discovered among Portuguese veterans of the war, many of whom had received blood transfusions or unsterile injections following injury, or had possibly frequented local prostitutes.