The rapid evolution of HIV in response to widespread drug treatment is making the virus less virulent and less likely to cause Aids, according to a study in Africa led by Oxford university.
The research, published in the journal Proceedings of the National Academy of Sciences, shows that HIV is following one of the theoretical predictions of epidemiology: that epidemics in new hosts gradually cause less severe disease as the pathogens evolve. HIV moved into humans from apes in the early 20th century.
In the case of HIV, this natural weakening has been accelerated by the extensive use of antiretroviral therapy (ART) drugs in Africa.
“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,” said Phillip Goulder, the study leader. “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 widespread use of ART is an important step towards the control of HIV,” added Mike Turner, head of immunobiology at the Wellcome Trust, which funded the study. “This research is a good example of how further research into HIV and drug resistance can help scientists to eliminate HIV.”
The research was carried out with more than 2,000 HIV-infected women in Botswana and South Africa, two countries hit hard by the virus. The key difference is that the epidemic has lasted a decade or so longer in Botswana.
The first part of the study showed that interaction between the human immune response and HIV leads to the virus becoming less virulent. People carrying a particular immune system gene called HLA-B*57 progress more slowly than usual to Aids.
In Botswana, where HIV has evolved further to adapt to HLA-B*57 than in South Africa, patients no longer benefit from the gene’s protective effect. But the data show that the cost of this adaptation is that HIV’s ability to replicate is significantly reduced, making it less virulent.
In the second part of the study the researchers developed a mathematical model, which concluded that drug treatment is accelerating the evolution of HIV variants with a weaker ability to replicate.
Independent experts said the study showed the benefit of maintaining and expanding HIV treatments while developing new drugs – and should not lead to complacency.
“If left untreated HIV still leads to Aids and death,” said Michael Brady, medical director at Terrence Higgins Trust, the leading UK Aids charity. “Our efforts should remain focused on encouraging the quarter of people with HIV in the UK who remain undiagnosed to come forward for testing and ensuring they have access to treatment and care as early as possible.”