WASHINGTON, Dec. 1 (Xinhua) -- The rapid evolution of human immunodeficiency virus (HIV), which has allowed the virus to develop resistance to patients' natural immunity, is at the same time slowing its ability to cause AIDS, according to new research conducted in over 2,000 African women.

The study, published Monday in the U.S. journal Proceedings of the National Academy of Sciences, also indicated that people infected by HIV are likely to progress to AIDS more slowly -- in other words the virus becomes less "virulent" -- because of widespread access to antiretroviral therapy (ART).

"If this proves to be the case, this process would substantially accelerate the success of current prevention and treatment programs that are designed ultimately to bring about population-level eradication of HIV," said the study.

Researchers enrolled over 2000 women with chronic HIV infection in Botswana and South Africa, two countries that have been worst affected by the HIV epidemic.

The first part of the study looked at whether the interaction between the body's natural immune response and HIV leads to the virus becoming less virulent.

People with a gene called HLA-B*57 are known to benefit from a 'protective effect' to HIV and progress more slowly than usual to AIDS.

This study showed that in Botswana, where HIV has evolved to adapt to HLA-B*57 more than in South Africa, patients no longer benefit from this gene's protective effect.

However, the team's data show that the cost of this adaptation to HIV is that its ability to replicate is significantly reduced, therefore making the virus less virulent.

The researchers then developed a mathematical model to examine the impact of ART on HIV virulence and found that selective treatment of people with low CD4 counts will accelerate the evolution of HIV variants with a weaker ability to replicate.

"This research highlights the fact that HIV adaptation to the most effective immune responses we can make against it comes at a significant cost to its ability to replicate," Professor Phillip Goulder from the University of Oxford, who led the study, said in a statement.

"Anything we can do to increase the pressure on HIV in this way may allow scientists to reduce the destructive power of HIV over time."

The study also included researchers from South Africa, Canada, Japan and the United States.