HIV evolution reducing its effect
The rapid evolution of HIV is reducing its ability to cause Aids, according to a study.
The report found that developing resistance to patients' natural immunity is causing the virus to become less deadly.
Researchers, led by the University of Oxford, concluded that this is making "an important contribution" in the fight against HIV.
They found that widespread access to anti-retroviral drugs was also slowing HIV's progress to Aids.
More than 2,000 women with chronic HIV infection in South Africa and Botswana - among the countries worst affected - took part in the study.
Scientists studied a gene in the human body that gives patients some protection against the effects of HIV. In Botswana, the virus has adapted to resist that gene's immunity, but this evolution has led to a reduced ability to replicate, making HIV less infectious and meaning it takes longer to cause Aids.
In the second part of the study, researchers found that the selective treatment of people with a low number of CD4 cells - a type of white blood cell that protects the body from infection - with anti-retroviral therapy (ART) accelerates the adaptation of HIV variants with a weaker ability to replicate.
Lead scientist Professor Phillip Goulder, from the University of Oxford, said: "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.
"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."
Mike Turner, head of infection and immunobiology at the Wellcome Trust, which funded the research, said: "The widespread use of ART is an important step towards the control of HIV.
"This research is a good example of how further research into HIV and drug resistance can help scientists to eliminate HIV."
The study was published in the journal Proceedings of the National Academy of Sciences.