The Pacifying of HIV
One of the most deadly diseases in the world, HIV and its more advanced counterpart stage AIDS were estimated to be present in 35 million people in 2013. 1.5 million died in the same year, with the overall death toll estimated at 39 million, making it the world’s leading infectious killer. HIV/AIDS does not kill the host directly, but weakens the immune system to the point where they are vulnerable to other diseases. Treatment for the disease is limited but improving, with antiretroviral drugs being the main course of action.
A recent study by the University of Oxford however has indicated that the virulent effects of HIV may be decreasing. There is wide belief that viral strains reduce their virulence over time through Natural Selection. Selection pressures are conflicted, with increased virulence decreasing host survival but also increasing the rate of transmission. The team at Oxford has been studying the reduction in viral replicative capacity (VRC) in patients from Botswana and South Africa. HIV has been prevalent in the former population for longer, and this was reflected by a reduction in VRC compared to the latter.
This reduction comes as an adaptation to the production of HLA molecules by the body. HLA molecules recruit a type of white blood cell which is used to destroy infected body cells. Selection pressures in the virus therefore favour mutations that evade these molecules, and these are known as escape mutants. They allow the virus to avoid being destroyed, but in turn reduce the virulence of the strain. The study found that HIV in patients from Botswana is better adapted to 2 of these HLA molecules, so much so that they no longer have a protective effect, but as a result the VRC is also much lower.
Not only is the body driving these changes, but also the use of antiretroviral drugs, which are used to control the symptoms of the disease, has been found to reduce the VRC of HIV. Although we are a long way from the disease becoming harmless, and this point will probably be surpassed by a cure, it is nonetheless good news.
Payne, R., Muenchhoff, M., Mann, J., Roberts, H., Matthews, P., Adland, E., Hempenstall, A., Huang, K., Brockman, M., Brumme, Z., Sinclair, M., Miura, T., Frater, J., Essex, M., Shapiro, R., Walker, B., Ndung’u, T., McLean, A., Carlson, J. and Goulder, P. (2014). Impact of HLA-driven HIV adaptation on virulence in populations of high HIV seroprevalence. Proc Natl Acad Sci USA, p.201413339.
Who.int, (2014). WHO | 10 facts on HIV/AIDS. [online] Available at: http://www.who.int/features/factfiles/hiv/facts/en/index8.html [Accessed 3 Dec. 2014].