The theory that HIV was introduced into humans through live oral polio vaccine in the late 1950s took a knock today with the news that careful examination of the rate at which HIV sub-types have diverged over the years suggests that it is highly likely that HIV first entered humans during the early part of the 20th century.
Using the equivalent of 512 supercomputers for a whole day to perform their calculations, Bette Korber and colleagues at the Los Alamos National Laboratory compared the genetic sequences of more than a hundred virus isolates, some dating from 1959 and the 1960s, to determine the average speed at which HIV sequences change over time. The group used this information to back-calculate the amount of time it would have taken HIV to mutate from the genetic sequence of SIVcpz, its nearest relative.
The calculations established that HIV-1 group M, the root of virtually all the HIV-1 sub-types found in humans, is highly likely to have entered humans from chimpanzees in Africa between 1910 and 1940. The calculations also found that the D sub-type (common in Africa) began to evolve before 1950, and that the B sub-type (common in Europe and North America) began to emerge from the D sub-type in the early 1960s.
However, Prof. Robin Weiss of the Windeyer Institute, University College, London, said that the findings did not completely rule out a role for polio vaccination campaigns in amplifying the epidemic, due to the re-use of needles.
A stimulating summary of debates about the origins of HIV can be found at http://weber.ucsd.edu/~jmoore/publications/HIVorigin.html
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Korber B et al. Timing the origin of the HIV-1 pandemic. Abstract L5, Seventh Conference on Retroviruses, San Francisco, 2000.