Scientists follow Aids trail back into jungle

By STEVE CONNOR

LONDON - As medical mysteries go, this one is about as 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, probably millions 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 week we should know whether it was the result of an experiment that went horribly wrong.

Novelist Joseph Conrad would be hard pressed to devise a better backdrop to the peculiar events shrouding the origin of Aids.

Why did a mystery illness seemingly emerge from the heart of Africa at the end of the 20th century?

Where did the Aids virus come from and how did it infect so many people without anyone realising the extent to which it had already spread?

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 which took place in the Belgian Congo at the end of the 1950s.

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 Western 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 doing several 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 chimp 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 rebut it.

But we might be in a better position to know next week, 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 issue 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 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, although some might still argue that absence of evidence is not absolute evidence of absence.

But, 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.

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, a Polish emigraacé scientist called Hilary Koprowski, vigorously defended their reputations.

The institute 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 had 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, when David Ho, a member of the Wistar committee, looked again at the Manchester research and found that there was no evidence of the seaman having been infected with HIV after all.

His conclusion undermined the single most important piece of evidence against the Congo vaccine theory. It meant that the question was once 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. Over a decade, Hooper obsessively interviewed hundreds of researchers involved in the Congo trials and produced a welter of circumstantial evidence to implicate the vaccine.

His book, The River, cites various reasons the polio vaccine caused Aids.

He says that Koprowski and the Wistar had never stipulated that they had used Asian monkeys and that chimp kidney tissue was an obvious culture medium for a live polio vaccine.

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

- INDEPENDENT