Chimps are not the only primates that carry viruses related to HIV. Earlier this decade scientists linked HIV-2 (a much rarer form of the virus found primarily in West Africa) to a monkey called the sooty mangabey. Mandrils and African green monkeys carry still other simian immuno-deficiency viruses (SIVs). The closest links to HIV-1 seemed to be three viral samples isolated in chimpanzees. But one of the three was so divergent from the other two that scientists doubted they were HIV-1’s immediate ancestors. To solve this puzzle, Hahn and her international team first had to fit the human and simian viruses into genetic ““family trees’’ that accounted for their similarities and differences. They next had to show that the chimps were in the same region where AIDS got its start in humans. In fact, the chimp subspecies lives in West Central Africa, the region where HIV-1 is thought to have originated. There was even a plausible mode of transmission from chimp to human. The animals have long been hunted for food, so blood from the carcasses could easily have entered the hunters’ bodies through superficial wounds. Hahn’s group showed how, after jumping species on at least three occasions, chimpanzee SIV evolved into the three families of HIV-1 strains recognized today.
The question is not merely of academic interest. The chimps, it seems, carry their version of the virus but do not get sick from it. In theory at least, they could reveal important clues about controlling AIDS. ““Humans share 98.5 percent of their genes with chimpanzees,’’ points out Dr. Feng Gao of UAB, one of Hahn’s collaborators. But just as scientists are learning the chimps’ value in AIDS research, this critical subpopulation is being hunted to the brink of extinction. Not only does that mean that hunters may be contracting additional viral strains; it also means that mankind is losing a living database of AIDS information. ““It’s like burning a whole library of books without having read them,’’ says Hahn. Given the similarity of man and chimp, it could prove a tragic loss. Who knows what other mysteries may be answered in those ““books’'?
