How to resolve the debate on the origin of AIDS.

Abstract

Although I agree with Edward Hooper (Letters, 18 Aug., p. [1140][1]) that the analysis by Korber et al . (Research Article, “Timing the ancestor of the HIV-1 pandemic strains,” 9 June, p. [1789][2]) is technically consistent with either an early or a late transmission of simian immunodeficiency virus (SIV) from chimps to humans (the principal origin of AIDS), we disagree on which of the two hypotheses is more likely in light of the presented data. In both cases, there are as-yet-uncollected data that could provide support for the respective hypotheses. If Hooper is correct that chimp SIVs were transmitted to humans from contaminated oral polio vaccines (OPVs) in the 1950s, then we should expect to see a large diversity of M-group viruses in present-day chimpanzee populations. Sampling to date has not revealed any such viruses, although more detailed sampling obviously should be undertaken. Finding diverse chimp SIVs that are phylogenetically embedded in the M group would support late, parallel transmission of the viruses into humans, consistent with Hooper's OPV hypothesis. In the case of the early transmission hypothesis, the missing data are positive HIV-1 samples from human sera from the 1930s and 1940s. However, according to the analysis by Korber et al ., even if HIV were already present in humans in 1930, there may have been as few as 10 or so humans infected with HIV-1 M-group strains in all of Africa as late as 1950. Given the small number of predicted infections in humans at this time, it would be numerically surprising if any positive HIV-1 samples were found in old serum samples from before the late 1950s, even if the virus had been slowly diversifying in human populations since 1930. In contrast, the chimp SIV M-group viruses should be relatively easy to find if the OPV hypothesis is correct, because they would be expected to be common in modern chimp populations. Unless direct evidence is found to support or refute the OPV hypothesis (such as a contaminated batch of OPV, or HIV-1 samples from humans from before the OPV trials), a thorough study of SIV variation in wild chimpanzee populations will be the best way to resolve this debate. [1]: /lookup/doi/10.1126/science.289.5482.1140 [2]: /lookup/doi/10.1126/science.288.5472.1789