Found at Last: the Chimps that Gave AIDS to the World

The Times (London)

Researchers have traced the origin of HIV -the virus that causes Aids -to chimpanzees in southern Cameroon.A virus identified in apes living in forests south of the Sanaga River is the closestfound to the human immunodeficiency virus.

The discovery bolsters the standard theory that the Aids epidemic began after an ape version of HIV crossed into people, most likely infecting a bushmeat hunter first.

Some conspiracy theorists have suggested that the virus was created in a bioweapons laboratory.

Another controversial hypothesis, advanced by the journalist Edward Hooper, holds that the epidemic began with a batch of contaminated polio vaccine in what is now the Democratic Republic of Congo. Neither scenario fits with the latest evidence.

Aids, or acquired immune deficiency syndrome, kills more than three million people a year worldwide.

The ape version of HIV, simian immunodeficiency virus (SIV), has long been considered the source of the human virus.

Chimps are by far the most likely species to have conveyed it to people. However, only a few captive animals have been identified as carrying chimp SIV (SIVcpz), leaving the wild reservoir of the virus that first infected people unknown. The possibility remained that another type of ape might have passed it on, and the location of the crossover was uncertain.

The international research team included Paul Sharp, Professor of Genetics at the University of Nottingham. Their findings are published today in the journal Science.

Trackers combed the forest floor at ten sites in Cameroon for chimp faeces, samples of which were sent for genetic analysis. This detected SIVcpz in up to 35 per cent of chimpanzees in some populations.

An evolutionary analysis of the genetic sequence of these chimp viruses has shown that it is very closely related to HIV-1.

Different chimp communities had slightly different genetic variants of SIVcpz.

Those closest to the human virus were found in southeast Cameroon.

Professor Sharp said that the work indicated that the HIV-1 virus, which causes Aids, almost certainly arose in this area in the early part of the 20th century.

"Particularly when you consider that HIV-1 probably originated more than 75 years ago, it is most unlikely that there are any viruses out there that will prove to be more closely related to the human virus," he said.

"Thus, the initial jump of a virus from a chimpanzee to a human probably occurred in that region."

As well as solving the mystery of the origin of the virus, the findings prepare the way for future work exploring the history and behaviour of the simian form of HIV in its natural host.

SIVcpz does not cause an Aids-like illness among chimpanzees, despite its similarity to the human virus and the very close genetic relationship between chimps and humans. Finding out why this is so could ultimately help scientists to understand the workings of HIV. Professor Sharp said: "We are currently working to understand which genetic differences between SIVcpz and HIV-1 evolved as a response to the species jump."

Copyright 2006 Times Newspapers Limited