AIDS: The new accusation

THE CHARGE: That what became the Aids virus was passed from chimp to man during experiments in the Congo to find a cure for polio. THE JURY: The world's leading Aids scientists, gathering in London next week to hear evidence at the Royal Society. THE VERDICT: will once and for all clear up one of medicine's greatest mysteries

As medical mysteries go, this one is about a big as they come. An unknown virus somehow emerges from the heat of a tropical jungle to cause one of the most frighteningly stealthy pandemics in history. Before doctors are even aware of the Aids virus, it has already infected hundreds of thousands of people around the world. Now scientists are on the verge of answering one of the most intriguing questions about the origin of Aids. Next Monday we should know whether it was the result of an experiment that went horribly wrong.

As medical mysteries go, this one is about a big as they come. An unknown virus somehow emerges from the heat of a tropical jungle to cause one of the most frighteningly stealthy pandemics in history. Before doctors are even aware of the Aids virus, it has already infected hundreds of thousands of people around the world. Now scientists are on the verge of answering one of the most intriguing questions about the origin of Aids. Next Monday we should know whether it was the result of an experiment that went horribly wrong.

Joseph Conrad himself would be hard-pressed to devise a better backdrop to the peculiar events shrouding the birth of Aids. Why did this illness seemingly burst out of Africa at the end of the 20th century? Where did it come from - and how did it infect so many people so quickly?

The answer might turn into the ultimate medical irony. A modern-day plague is unleashed with the unwitting help of doctors trying to fight another, equally appalling disease. If true, it means that Aids was a terrible side-effect of the polio vaccination campaign that took place in the Belgian Congo at the end of the Fifties. If false, the allegations would amount to a damaging slur on an heroic attempt to rid the world of a devastating paralysis.

The story starts in 1957 with a team of scientists who established a remote chimpanzee colony on the edge of the Congolese jungle. The colony was run by a private biomedical research foundation, the Wistar Institute of Philadelphia, which was engaged in a number of medical projects, including an attempt to develop a polio vaccine.

Up to 400 wild chimps eventually passed through the camp, many dying in scientific experiments that would constitute dubious practice by today's animal-welfare standards. But this story is not about man's inhumanity to his fellow primate; it is about whether a virus that naturally resides in chimps could have taken the novel opportunity provided by the experiments to jump the "species barrier" separating humans from their nearest living relative. In short, could a contaminated batch of polio vaccine made from infected chimpanzee tissue have resulted in an Aids virus passing from ape to man?

The idea first emerged publicly in 1992 in an article in Rolling Stone magazine, but with little hard evidence to support or refute it. However, we might be in a better position to know on Monday, when leading Aids scientists from around the world meet at the Royal Society in London to discuss the latest developments in the controversy. The Wistar Institute is expected to release the findings of three independent laboratories that were asked to search for remnants of contaminated chimp tissue in stocks of the same polio vaccine stored in the Wistar vaults for more than 40 years.

The results of the tests and even the names of the laboratories are a closely guarded secret. The scientists looked for two things: the presence of chimpanzee tissue and the DNA of the chimpanzee virus closely related to HIV, a virus known as SIV. If the researchers find neither, the polio vaccine campaign is cleared.

However, should the test results indicate that the vaccine does indeed contain chimp tissue, it would undermine the Wistar Institute's repeated assertions that no chimp tissue was ever used to make its polio vaccine. The institute has always insisted that it made polio vaccine by growing it in the tissue of Asian macaque monkeys, which are not naturally infected with SIV. (Monkey tissue provides a good medium for culturing live, attenutated vaccines.)

If the tests also show that the vaccine samples contain the genetic material of SIV, then this would provide overwhelming support for the idea that the polio vaccine trials led to the Aids epidemic. It would mean in effect that the smoking gun has finally fired a bullet.

In the aftermath of the 1992 article, the Wistar Institute and the inventor of its polio vaccine, Hilary Koprowski, vigorously defended their reputations. Koprowski, now in his eighties, took legal advice and forced the magazine to publish a "clarification". The magazine stated that it had no scientific proof that Dr Koprowski's vaccine was responsible for the Aids pandemic or that he was involved in bad practice.

It went on: "Dr Koprowski's pio- neering work in developing polio vaccines has helped spare suffering and death to hundreds of thousands of potential victims of paralytic poliomyelitis and is perhaps one of his greatest contributions in a lifetime of high and widely recognised achievements."

Meanwhile, the Wistar set up an independent committee of six scientists to review the evidence for themselves. Their conclusion was that any "theoretical possibility" was "extremely low". A central plank of the evidence against the theory was the discovery of HIV in a preserved piece of tissue from a Manchester seaman who died in 1959 and had returned from his travels before the Congo trial began. The Wistar committee, citing this evidence, added: "It can be stated with almost complete certainty that the large polio vaccine trial begun in 1957 in the Congo was not the origin of Aids."

There the matter rested until 1995. One of the members of the Wistar Committee, David Ho, had looked again at the Manchester research. Ho, a brilliant virologist who was once voted man of the year by Time magazine, found that there was no evidence for the seaman to be infected with HIV after all. His findings, first published by The Independent, eventually led to an embarrassing retraction in The Lancet by the University of Manchester scientists.

Ho's conclusion also undermined the single most important piece of evidence against the vaccine theory. It meant that the question was again raised: could the polio vaccine trial have introduced SIV into the human population which led to the HIV epidemic?

Last year the question was seemingly answered in a book by Edward Hooper, a former BBC journalist who had spent many years in central Africa and had probably followed the debate more closely than any other non-scientist. Hooper had obsessively spent a decade interviewing hundreds of researchers involved in the Congo trials and produced a welter of circumstantial evidence to implicate the vaccine.

He managed to enlist the support of a powerful ally in Professor Bill Hamilton, a brilliant evolutionary biologist at Oxford University. Hamilton championed Hooper all the way, and as a fellow of the Royal Society was involved in arranging next week's meeting. Unfortunately, while in the jungle to collect evidence to support the theory, Hamilton contracted malaria and died this year.

Hooper's book, The River, cites various reasons why the polio vaccine, called "CHAT", was the cause of Aids. He points to the apparent geographical correlation between outbreaks of early cases of Aids and the use of the vaccine between 1957 and 1960. He says that Koprowski and the Wistar had never stipulated that they used Asian monkeys and that chimp kidney tissue was an obvious culture medium for a live polio vaccine.

Hooper claims that former workers at the chimpanzee camp at Lindi in the Congo told him that chimp tissue was used for polio work, something the Wistar has denied. In summary, Hooper manages to build up a convincing argument but fails to find that crucial piece of documentation or scientific evidence to clinch the matter.

John Moore, a British virologist at the Rockefeller University in New York, and former colleague of Ho's, says Hooper's arguments are "entirely implausible". He has denounced Monday's meeting as a waste of time. "Would astrophysicists think it worthwhile to discuss whether the moon is made of green cheese?"

Paul Sharp, a specialist in HIV evolution at the University of Nottingham, says that while there is little doubt over the fact that HIV jumped from chimp to humans, the barrier was crossed a couple of decades before the Congo trial. It most probably resulted from close, bloody contact between chimps and human hunters. The idea that the polio vaccine could have provided the bridge between the two species is "nonsense", says Sharp.

"It's not nonsense," says Simon Wain-Hobson, an Aids researcher at the Pasteur Institute in Paris. "But I think on the evidence available a jury would not be able to convict. In terms of the Congo vaccine, a jury would have to say 'not guilty'. It would be very nice to prove the vaccine theory wrong, but I don't think the demolition job has been done. The idea is not impossible."

Perhaps the most telling comment comes from David Ho, who still sits on the Wistar Committee, and is personally convinced of scientific data indicating that HIV evolution began to explode in the Thirties, when huge changes began to occur to Africa's traditional rural way of life. Ho is firmly of the opinion that SIV in chimpanzees probably jumped to humans many times in the past, but they ended up being "dead-end" transfers which failed to ignite an epidemic. "We have to say several transfers occurred in the past but they never propagated. The one that did probably took place 60 or 70 years ago, and it propagated very slowly," Ho says.

As regards the Hooper hypothesis, Ho lets slip a comment that might indicate the way the Royal Society's meeting is likely to go. "While the Ed Hooper scenario is plausible, it is extremely unlikely and I think he'll be proven incorrect in the long run."

Whatever the outcome, the meeting next week is likely to lift the veil on one of history's most intriguing medical mysteries.

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