A new study suggests that HIV may have affected humans much longer than is currently believed. In fact, the virus might have been around undetected for so many centuries that a human community developed some degree of resistance to the virus.

It is generally believed that HIV originated from chimpanzees in central Africa that were infected with simian immunodeficiency virus (SIV), which is also 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," said Alfred Roca, an assistant professor in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois.

The type of HIV that is associated with 90 percent of all HIV infections - HIV-1 M - is said to have migrated from chimps to humans between 1884 and 1924.

However, Roca said that this virus might have been infecting isolated groups of people many years before it was detected.

"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," Roca said.

Another important factor is that the modern medicine with drugs and vaccines can keep people alive for many years. Earlier, people with a compromised immune system, characteristic of HIV infection, died early meaning that the virus didn't get a chance to spread.

Roca and colleagues then hypothesized that if HIV was affecting people for such a long time, then selection might have favored genetic traits that had a protective effect on the human population. To look for evidence, his team analyzed genetic map of people belonging to BiAka people.

The BiAka are nomadic pygmy people that live in the forests of Africa inhabited by the chimpanzee subspecies believed to be the source of the current HIV outbreak. Researchers compared genome of this community with four other African communities that live outside the chimpanzee's range.

They found that out of the five communities, the BiAka people had the genetic variations that increased their resistance against HIV infection. The genetic traits either affected the virus' ability to infect host cells or the progression of the disease.

However, Roca said that the study results are inconclusive and that there is a possibility of false positives affecting the study results.

"If additional studies confirm that these genes have undergone selection and that human populations in the region have some genetic resistance to HIV-1, one could try to find additional genes in the population that may also be protective against HIV but have not yet been identified," he said.

Roca added that further research could determine the mechanism by which the genes fight HIV and this in turn could open up new ways of defeating the virus.

Around 34 million people in the world are now living with HIV. Of these, 54 percent have access to antiretroviral therapy, according to World Health Organization. Sub-Saharan Africa is highly affected by HIV where one in every 20 adults is HIV positive. About 69 percent of all people who have HIV live in this region.

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