Origin of Aids pinpointed

By STEVE CONNOR

Scientific sleuths have pinpointed the precise origin of the Aids virus in a study showing that HIV came about when two monkey viruses hybridised in the body of an infected chimpanzee.

The scientists found that wild chimps became infected simultaneously with two simian immunodeficiency viruses (SIVs) which had "viral sex" to form a third virus capable of infecting humans and causing Aids.

The findings are the culmination of 10 years of research into the Aids virus by Paul Sharp of Nottingham University and Beatrice Hahn of the University of Alabama.

One implication of the research - published in the journal Science - is that chimps may still be acting as "mixing vessels" for other monkey viruses.

"Because of the similarity between chimpanzees and humans, any virus that successfully adapts to spreading among chimpanzees would be a candidate for a further jump to humans - a potential HIV-3," Professor Sharp said.

It was already established that HIV-2 - the Aids virus prevalent in West Africa - evolved from a strain of SIV that infects sooty mangabey monkeys, which have been hunted by humans for food.

It was also known that the closest relative to HIV-1, the principle Aids virus, was found to be an SIV that infects chimpanzees in central Africa. But until now it was not clear how this virus had come into existence.



Scientists believe that the hybridisation - technically known as recombination - took place inside chimps that had become co-infected with both strains of SIV after hunting and killing the two smaller species of monkey.

The scientists found that the left and right halves of the genome of SIV in chimps closely match the genomes of SIV in red-capped mangabeys and greater spot-nosed monkeys.

"It appears that, in the past, chimpanzees have picked up viruses from both monkeys, and then the hybrids formed by recombination between the two viruses," Professor Sharp said.

"This hybrid virus spread through the chimpanzee species and was later transmitted to humans to become HIV-1.

"Chimpanzees commonly hunt and eat monkeys, and this most likely provided the route by which they acquired these monkey viruses.

"This is similar to the means by which humans probably first became infected [with HIV], by butchering chimpanzees for 'bushmeat'."





It has been difficult to disentangle the evolutionary relationships between different strains of SIV but new techniques developed by the team allowed the scientists to identify the chimp virus as being a hybrid.

Professor Sharp was one of the first HIV scientists to show that some HIVs infecting humans were hybrids of two or more Aids viruses that had infected the same person at the same time.

The HIV trail

Scientists believe chimps ate monkeys infected with separate viruses

The viruses combined.

When humans ate the infected chimps, the HIV/Aids virus began.


Herald Feature: Health

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