HIV-AIDS did not come from oral polio vaccine contaminated with chimpanzee virus, according to findings from an expedition designed to test the hypothesis by one of its key sympathisers. The findings are published online in the April 22nd edition of Nature.
The theory that the HIV epidemic originated from the animal to human transfer of simian immunodeficiency virus (SIV) through oral polio vaccine developed in the 1950s gained much prominence following the publication of Edward Hooper’s investigation, The River, in 1999. In this book Hooper alleged that an early version of oral polio vaccine was developed at research stations in the then Belgian Congo, using cells from locally sourced chimpanzees that might have contained SIV, the primate equivalent of HIV.
Polio vaccine developers responded to the book’s arguments by testing a batch of early polio vaccine in the possession of the Wistar Institute in Philadelphia. Although this sample was found to contain no traces of HIV, Hooper argued that these samples were irrelevant since they had not been prepared for trials in Africa, and that only one batch of vaccine (prepared at a research station near Kisangani) could have been contaminated, according to the accounts of research assistants he had tracked down.
Hooper was supported in his efforts to investigate the links between HIV and oral polio vaccine by the Oxford University evolutionary biologist Bill Hamilton, who argued that only by taking samples from chimpanzees that could be found in the vicinity of Kisangani today would it be possible to determine whether the variant of SIV present in the local primate population might have provided the ancestor for HIV-1 group M.
So, in 2000, Michael Worobey, an assistant professor of ecology and evolutionary biology at the University of Arizona in Tucson, and Bill Hamilton went to the Democratic Republic of Congo to collect chimpanzee faeces. By collecting fresh samples they hoped to recover enough viral RNA to determine whether chimpanzees in the Kisangani region harboured the ancestor of HIV.
He worked with a team of hunters that tracked the chimps at night using their calls. The team carefully stored small samples of faeces in little screw-capped vials filled with a preservative.
The 2000 trip met with some calamities. Worobey contracted blood poisoning from a rattan palm spike that stabbed his hand. He hiked out of the forest to seek medical attention. His two companions, Jeffrey Joy and Bill Hamilton, came down with malaria. Hamilton later died from complications.
The faeces collected on that trip didn't yield any SIV genetic material, although tests of chimpanzee urine suggested that virus from the SIVcpz family was present in some of the chimps.
On his 2003 trip, Worobey was luckier. Although he hiked about 200 miles through the rainforest collecting samples, he did not fall ill.
Even so, out of 97 different samples collected, only one contained any SIV. But that was enough -- the analysis revealed a brand-new strain, which Worobey and his colleagues named SIVcpzDRC1.
"Bill (Hamilton) died after that first trip, and that's why it was so nice to go back and finish what we started," Worobey said. "I was surprised that we finally got something after so much blood and toil and tears and sweat -- but not surprised where the virus fell on the phylogenetic tree. It’s not closely related to HIV-1."
The sequence of the new SIV's genetic material definitively shows that HIV-1 didn't come from chimpanzees in that area, he said.
"This is one of only a handful of places in the world where SIVs are known to be circulating in chimpanzees. We know HIV-1 comes from chimpanzees, but we know little beyond this," he said. "I want to study this geographic area -- get more samples, understand how the virus is maintained and transmitted in chimps, and understand why the virus is so pathogenic in humans but not chimpanzees."
However, Edward Hooper is unlikely to accept that the findings lay to rest the oral polio vaccine controversy. In an article published by the London Review of Books in April 2003, Hooper noted that only six SIV sequences from wild chimpanzees throughout the Congo had been published by that time, and that these indicated huge divergence in SIVcpz.
He cited the geneticist Mikkel Schierup of the University of Aarhus, Denmark, an expert on HIV recombination, who has pointed out that all it would have required to generate the diversity of HIV-1 variants seen in the world today would be two different chimp SIVs which somehow recombined in humans. Such an event could have happened in vivo (for example in human vaccinees) or in vitro (for instance in polio vaccines cultured in chimp cells).
He also notes that chimpanzees at the Lindi research station near Kisangani were collected from a 100,000 square mile area in the Congo.
Other researchers, including Professor Paul Sharp of the University of Nottingham, a co-author of the study, have argued that the oral polio vaccine theory is invalidated by the rate of divergence of HIV from a possible common ancestor. They believe that a transfer date during the 1930s is more plausible and argue that the hunting and eating of chimpanzees was likely to have been the transfer route for the virus.