Rethink begins into how the virus originated

Steve Connor analyses how the Carr case affects theories on Aids

It did not take long for conspiracy theories to germinate in the fertile territory of the early Aids years. Where did this virus come from and what was responsible for spreading the global epidemic?

A cartoon in Pravda in the Soviet Union exemplified the spirit of the mid-1980s. It depicted an American scientist in a white lab coat handing over a test-tube full of tiny swastikas to a US general, who dishes out dollar bills in return for the gift of HIV. Few Soviet bloc scientists believed such propaganda, of course, and still fewer Western researchers had any time for the equally conspiratorial suggestion that Aids was a product of a Soviet germ-warfare laboratory.

Other more scientifically based theories began to emerge when scientists discovered in 1985 that monkeys had an Aids virus of their own, called simian immunodeficiency virus, SIV. Because of its close genetic affinity with HIV, scientists postulated that the human virus must have evolved from the monkey virus at some point in history. Wild populations of African green monkeys, about a third of which are infected with SIV, became the key suspect.

However, people in Africa had been capturing and butchering monkeys for generations and yet Aids seemed to be a new disease which, even with the benefit of hindsight, only began to appear in the 1970s.

Perhaps the event that led to SIV crossing the ``species barrier'' from monkey to humans was something quite different. One idea focused on the use of kidney cells from African monkeys to make an oral polio vaccine which was distributed in the Belgian Congo between 1957 and 1960 as part of a World Health organisation programme.

The theory had several drawbacks, but one was especially significant. The world's first confirmed case of Aids and HIV was a Manchester man who had died in 1959. He had become ill the previous year and was most likely to have been infected with HIV before the Congo trial had even begun. Now, as the Independent has revealed, there is no evidence that this man had been HIV positive, but where does this lead the polio vaccine theory and the origin of Aids?

Even with the Manchester case discredited, there are other serious objections. The chances of SIV being transmitted orally in such a vaccine are low, and another oral polio vaccine made from kidney cells, distributed in Eastern Europe at about the same time, had not caused an Aids epidemic there.

Until today, the Manchester case provided scientists with another problem. They were confused about why this virus was almost identical to strains of HIV circulating more than 30 years later. This meant the ``molecular clock'' that ticks away during the evolution of a virus was running far more slowly than they had imagined, suggesting that HIV had infected humanity for centuries.

If it was correct that HIV had not changed significantly in more than 30 years, it would have startling implications for the evolution of the human virus from its monkey virus ancestors. If in 30 years the virus had not changed to any large extent, then it meant that HIV was an ancient virus, perhaps centuries old. In fact, David Ho, at the Aaron Diamond Aids Research Centre in New York, and Gerry Myers, at the Los Alamos National Laboratory in New Mexico, had calculated that if the 1959 virus was genuine, it would mean that the simian ancestor of today's HIV crossed from monkeys to man about eight centuries ago.

This went against just about everything Dr Myers had learnt about HIV evolution. All his research suggested this jumping across the "species barrier'' was far more recent, perhaps just a few decades ago. Now the Manchester case has been discredited, he is convinced that HIV is a recent human pathogen, perhaps evolving from the monkey SIV just 35 years ago.

Although there have been other claims of HIV being detected in stored tissue samples dating back to the 1960s, none have been confirmed. In fact, the earliest confirmed case of HIV, dates back to a blood sample collected in Africa in 1976.

Dr Myers said: ``It is extremely difficult to find any evidence of HIV infection before the end of the 1970s. For example in a recent survey of 250 Zairean [blood] samples stored since 1969, not a single infected sample was found." This does not mean HIV was not there, it just means it was not common enough to be detected by analysing stored tissue or blood samples, he says.

Eliminating the Manchester samples has bolstered his view that HIV came into being very recently and that something happened in the past 20 or so years to cause Aids' explosive spread into a global epidemic.

The realisation that the human Aids virus is after all a genuinely new infectious agent has once more focused attention on what were the unusual circumstances that led to the origin of HIV about 35 years ago.

One plausible theory is that the hunting and capturing of African monkeys for research labs in Europe and the US is responsible. This is intriguing because the time suggested by evolutionary theory as the origin of HIV from SIV coincides with a marked growth in the trade of wild African monkeys for research purposes.

In the late 1950s, the Indian government had put an embargo on the export of the Asian macaque monkey, and this led to more African monkeys being captured for export to research institutes in the West. In addition to bringing more people into contact with living monkeys that were infected with SIV, it is reasonable to suppose that the nature of the contact may have been different. The animals would have been kept captive for long periods with ample opportunity for handlers to be bitten or scratched.

During the same period, there was also a rapid growth in the use of re-usable syringes and hypodermic needles in Africa, which was undoubtedly the original epicentre of the global epidemic. Along with traditional scarification - where the same instrument would be used to scar the skin of many people - this provided ideal conditions for a new human virus to spread.

Dr Myers believes that HIV1 must have crossed the species barrier from monkey to humans not once but twice. "At the moment the evidence points to these [HIV] viruses having emanated from two different ancestors over just the last 30 or 35 years. And the reason why this exercise is worthwhile is that it tells us what we should expect in the coming 30 years. If it took only this long for the amount of diversification [of HIV] we see today, then by the year 2010 we should expect this much again.''