“What we’ve found, says Dr. Paul Sharp, a geneticist at the University of Nottingham and one of the researchers involved,” is that the virus most closely related to the human virus – HIV–1 – comes from a specific subspecies of chimpanzee. The results arrived from comparisons of the genetic material of various sequences of SIV (or Simian Immuno–deficiency Virus which affects chimpanzees) to the sequences of the human virus.
As Sharp explains, while there are a number of viruses similar to HIV found in African primate species, only one is unmistakably related to the virus that leads to AIDS in humans. And it’s no coincidence that the SIV found in Pan troglodytes appears in the Cameroon – Gabon region of central–west Africa.
That’s precisely where the first documented cases of HIV and AIDS emerged. But how and why it was transferred to humans is still a matter of inference and speculation, according to Sharp.
“As well as the particular subspecies of chimpanzees that have transmitted the virus to humans, there is also another subspecies that also has a divergent virus”, Sharp points out. And what we infer from that is that a common ancestor to those chimpanzees was probably infected with SIV. That might have happened hundreds of thousands of years ago. However, the virus has probably been transmitted to humans on many, many occasions over thousands of years.
The simplest explanation of how that may have occurred is that, in areas of Africa, people hunt chimpanzees and eat them and have been doing so for quite a long time. But the risk of infection comes not so much from eating the meat as much as from the process of butchering the animals.
“There would be many opportunities for blood from chimpanzees to splash on to an open wound of a human”, Sharp explains, and that would be sufficient for the virus to jump from a chimpanzee to the human.
Both SIV and HIV emerged from the same region of Central West Africa
Central West AfricaBut why SIV began to ravage humans only 20 or 30 years ago is also a matter of inference. “It could be changes in the population structure in Africa in the second half of this century that have allowed the virus to get out and start a pandemic,” he suggests. The massive migration of rural Africans to much larger cities, as well as disruptions to populations caused by civil wars are just two possibilities.
Despite such guesstimates, however, this discovery may have a profound scientific legacy. As Sharp puts it, “it really focuses our attention on where we should be looking for more clues about how to combat AIDS.” That’s because, as far as science can determine, chimpanzees infected with SIV don’t suffer any AIDS–like symptoms. “We have essentially the same virus infecting one species – the chimpanzee – and not causing disease, and then making another species – humans – contract a disease,” he points out. “It obviously raises the question, ‘Why is there that difference in the progression of the infection?’ And that really points us to that new direction.”