At current rates of infection and mortality, a teenage boy in Botswana has about a 90% chance of dying of AIDS. Researchers have calculated that in some African countries over the next century, there will be natural selection for genotypes that decrease a personís susceptibility to HIV infection and increase the time to onset of AIDS. The payoff for extending this interval will be to prolong the victimís survival at his or her time of peak fertility.
One factor in susceptibility to HIV infection and the time taken for infection to progress to full-blown AIDS is the form of a receptor molecule found on the surface of cells, called CCR5 in some people. In a Brief Communication (Nature, Vol. 411, No. 6837, 31 May 200), Paul Schliekelman and colleagues, of the University of California, Berkeley, model how the more resistant forms of CCR5, which now extend the lifespan of an HIV-positive person by 2 to 4 years, will spread through sub-Saharan Africa. Over the 100-year timespan of the simulation, the AIDS-delaying form of CCR5 will rise in frequency so that more than 50% of the population will carry it.
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