Globally circulating strains of HIV-1 responsible for the global AIDS epidemic originated in an African chimpanzee. The major-group viruses that dominate the global AIDS pandemic shared a common ancestor in the 1940s or the early 1950s that was probably introduced into humans shortly before that time. The other two HIV-1 groups have each arisen as a consequence of independent transmissions of SIVcpz from Pan troglodytes troglodytes to man. Chimpanzees have been natural reservoir of SIVcpz for several hundred thousand years. Chimpanzees are commonly hunted for food, especially in west equatorial Africa. Hunters dismember chimpanzees with primitive butchery, and so expose themselves to the risk of transmitted disease.

The oldest trace of the AIDS pandemic is from a human blood sample collected in 1959 from west central Africa. The factors that propelled the initial spread of HIV-1 in central Africa remain unknown: the role of large scale vaccination campaigns, perhaps with multiple uses of non sterilized needles, should be carefully examined, although social changes such as easier access to transportation, increasing population density and more frequent sexual contacts may have been more important.

If the global epidemic was founded by a single HIV, it is no different from the annual 'flu strain. It seems to have occurred around, or just after, the Second World War. The post-war era saw the collapse of European colonialism and attendant changes in urban and technological traits.

This is an important finding with significant potential. Study of infected chimpanzees in the wild may enable us to find out why these animals don't get sick, information that may help us better protect humans from developing AIDS.

HIV-1 has a faster disease course and more efficient transmission than HIV-2, which is mainly found in parts of Africa.

Animals carry many viruses that may not harm them but have more serious consequences when transmitted to humans. Influenza, for example, is harbored by ducks, chickens and pigs and new variants can easily spread to humans, touching off major epidemics.

FENG GAO et al: Origin of HIV-1 in the chimpanzee Pan troglodytes troglodytes
Nature 397, 436-441 (1999) Letters to Nature
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