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Were chimps the source of HIV? Charles Gilks on Edward Hooper's controversial book

The River: A Journey Back to the Source of HIV and AIDS by Edward Hooper, Little Brown, £25/$35, ISBN 0316372617

New Scientist, 13 November 1999, pages 54-55.

FACED with tragedy and terror, it is very human to ask why? HIV/AIDS is undoubtedly the most terrifying of all emerging human diseases. More than 35 million people are infected or sick, around 16 million have already died and worldwide at least 6000 people become infected every day. The strength of Edward Hooper's obsession with the question matches the scale of the pandemic. How did it start? Is anyone to blame? Could it happen again?

The fundamental facts are now largely undisputed. AIDS is a new disease. It is caused by two related retroviruses: HIV-1 and HIV-2. The pandemic is caused by HIV-1; HIV-2 is not common outside West Africa. Each subtype has several distinct lineages. The earliest confirmed evidence of human infection dates from 1959, in Leopoldville (now Kinshasa) in what was then the Belgian Congo. African primates harbour very similar viruses that do not appear to cause them any ill effects: chimpanzees carry an equivalent of HIV-1, and the sooty mangabey HIV-2.

Beyond these bare bones, a plethora of accusations, false starts and political intrigues has bedevilled scientific inquiry. In The River, Hooper details them all with immense scholarship, providing what will surely be the definitive chronicle of the opening of the AIDS era--and a highly readable one, no mean achievement.

A journalist, Hooper tells it as one of the great stories of the century, and it is one in which he is a player. He was actively involved, for example, in unravelling the saga of the Manchester sailor who died in 1959 and was erroneously and posthumously diagnosed as the first person to die of AIDS. Hooper tracked down the sailor's fiancée, the doctors involved, and his national service records in search of evidence of contacts with Africa. He pressed to get viral RNA from the sailor's stored tissues sequenced, and was a co-author of the paper in Nature that finally showed that the diagnosis was caused by later contamination, not an original HIV infection. Chronology is the book's main weakness, though, and we have to wait 46 chapters to learn this denouement of the Manchester story.

What, then, was the source of HIV? The standard view is that humans in Africa were infected through killing and preparing "bush meat"--wild-caught monkey--which is often a bloody process. The monkey virus became virulent in its new host. Diseases have probably crossed species by such routes quite often in the past. But, even when the hunters survived long enough to infect others, there was limited potential for spread in the geographically restricted tribal groups. Only the massive social changes following colonisation and urbanisation offered HIV access to wider communities in Africa and beyond.

Hooper has a different theory. He believes that an oral polio vaccine, CHAT, was involved. He thoroughly charts its development by American virologist Hilary Koprowski in the 1950s as it was tested and used in the Belgian Congo and on a small scale in Poland. Hooper finds inconsistencies and vagueness as he surveys reports and recollections of these events nearly fifty years ago. In particular, Hooper examines the question of whether or not chimpanzee kidneys were used in the cell cultures in which the attenuated polio strain was grown in the Congo. Was this the path the virus trod?

The use of the vaccine does correlate well with the first recorded cases of HIV-1 infection and Hooper is persuasive that it is possible, even likely, that chimpanzees were used. They may not have been the chimp subspecies Pan troglodytes troglodytes in which viruses ancestral to HIV-1 have been found, but then the distribution of retroviruses in wild chimps is very poorly documented.

Hundreds of thousands of doses of CHAT were undoubtedly given--and it is just about possible that an oral vaccine could infect through the tonsils. But the vaccine was given mostly to young children and, had they been been infected with HIV, few would have survived to sexual maturity and activity.

Hooper is clear about how to test his theory. He wants samples of the CHAT vaccine located, and its DNA and RNA content sequenced. But many batches of the vaccine were produced, so a single negative result will not reassure him and a positive result indicating retroviral contamination cannot prove his theory.

I remain sceptical. Oral transmission does not convincingly explain the existence of several lineages of HIV-1, nor the multiple origins of HIV-2 from mangabeys in West Africa. But several of my colleagues are not. You really should read the book and make up our own mind.

The worrying question is, could history repeat itself? What other diseases could leap at us out of the forest? If bush meat was responsible, stopping the trade would eliminate such threats. But whatever may have happened in the 1950s, today it would be almost impossible for properly manufactured modern vaccines to be contaminated with extraneous pathogens. It is important to reassure.

Charles Gilks is head of tropical medicine at the Liverpool School of Tropical Medicine. He has been working on HIV/AIDS in Africa for 12 years.