Researchers led by Alfred Roca from the University of Illinois believe that the genomes of an isolated West African human population provide important clues about how the disease has evolved.
HIV is thought to have originated from chimpanzees in central Africa that were infected with simian immunodeficiency virus (SIV), a retrovirus.
"If you look at the diversity present across SIV in chimpanzees, it suggests that they have had it for tens of thousands of years," Roca said in a statement.
HIV-1 Type M, which accounts for 90 per cent of human infections, is believed to have crossed the species barrier into human populations between 1884 and 1924.
Roca said that it may have crossed much earlier and many times, selecting for genetic resistance in isolated rural populations while remaining undetected.
"Some of the scientific literature suggests that the persistence of HIV in humans required population densities typical of the larger cities that appeared in West Central Africa during the colonial era," he said.
Perhaps an even more important factor is that, before modern medicine and vaccinations, infectious diseases such as smallpox killed large numbers of people. People with compromised immune systems may have succumbed first, preventing the immunodeficiency virus from spreading.
If HIV crossed the species barrier many times, it is possible that selection favoured protective genetic variants in the affected populations. Roca and his co-investigators looked for evidence of this selection in the Biaka genomes.
The Biaka are a human community that inhabits forests in the range of the chimpanzee subspecies believed to be the source of the current HIV pandemic.
Researchers compared Biaka genomes with the genomes of four other African populations who live outside the chimpanzee's range.
Biaka genotypes were available through the Human Genome Diversity Project, which collected biological samples from 52 different population groups across the world.
They identified four genes in these overlaps that code for proteins affecting either the ability of HIV to infect the host cell or the disease progression. The researchers also found that for several genes, SNPs associated with protection against HIV-1 were common among the Biaka.
Roca cautions that these results should not be considered definitive. It is not possible to rule out false positives.
