New research indicates that the most pervasive global strain of HIV began spreading among humans between 1884 and 1924, not during the 1930s, as previously reported. The earlier period of origin coincides with the establishment of urban centers in the west-central African region where the epidemic of this particular HIV strain--HIV-1 group M--emerged. This suggests that urbanization and associated high-risk behaviors set the stage for the HIV/AIDS pandemic.
The research, led by Michael Worobey, D. Phil., of the University of Arizona in Tucson, was co-sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.
To reach this earlier estimation of the origin of HIV, a team of scientists from four continents screened multiple tissue samples and uncovered the world's second-oldest genetic sequence of HIV-1 group M, which dates from 1960. The scientists then used it along with dozens of other previously known HIV-1 genetic sequences to construct a range of plausible family trees for this viral strain. The lengths of the tree branches represent the periods of time when the virus genetically diverged from its ancestors. The timing and number of these genetic mutations enabled the scientists to calibrate the probable range of rates at which the trees have grown--that is, the probable rates of evolution of HIV-1 group M. Based on this range of rates, the scientists projected back in time to the period when the trees most likely took root: around the turn of the 20th century. This marks the probable time of origin of HIV-1 group M, according to the researchers.
Using newly developed techniques, the scientists recovered the 48-year-old HIV gene fragments from a wax-embedded lymph-node tissue biopsy from a woman in Kinshasa in the Democratic Republic of the Congo. The oldest known HIV-1 group M genetic sequence comes from a 1959 blood sample from a man also from Kinshasa. A comparison of the same genetic region in the 1959 virus and the 1960 virus provided additional evidence that their common ancestor existed around 1900. The comparison revealed that the amount of genetic divergence between these two HIV sequences took more than 40 years to evolve.
ARTICLE: Worobey et al. Direct evidence of extensive diversity of HIV-1 in Kinshasa by 1960. Nature DOI: 10.1038/nature07390 (2008).
WHO: Anthony S. Fauci, M.D., NIAID Director, and Rosemary McKaig, M.P.H., Ph.D., a program officer in NIAID's Division of AIDS, are available to comment on this article.
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