HIV This Week

Nagelkerke N, de Vlas SJ, Jha P, Luo M, Plummer FA, Kaul R. Heterogeneity in host HIV susceptibility as a potential contributor to recent HIV prevalence declines in Africa. AIDS. 2009;23(1):125-30.

HIV prevalence has recently declined in several African countries, and prior to this the risk of HIV acquisition per unprotected sex contact also declined in Kenyan sex workers. Nagelkerke and colleagues hypothesized that heterogeneity in HIV host susceptibility might underpin both of these observations. A compartmental mathematical model was used to explore the potential impact of heterogeneity in susceptibility to HIV infection on epidemic behaviour, in the absence of other causative mechanisms. Studies indicated that a substantial heterogeneity in susceptibility to HIV infection may lead to an epidemic that peaks and then declines due to a depletion of the most susceptible individuals, even without changes in sexual behaviour. This effect was most notable in high-risk groups such as female sex workers and was consistent with empirical data. Declines in HIV prevalence may have other causes in addition to behaviour change, including heterogeneity in host HIV susceptibility. There is a need to further study this heterogeneity and its correlates, particularly as it confounds the ability to attribute HIV epidemic shifts to specific interventions, including behaviour change.

Editors’ note: Although there is compelling evidence that the HIV prevalence declines observed in many parts of Africa were likely caused by changes in risk behaviour, this model predicts that unevenly distributed susceptibility may have played a role. Genetic, immune, and infectious correlates of altered susceptibility mean that early HIV acquisition by more susceptible hosts may leave behind more resistant populations with reduced HIV incidence. Despite these underlying epidemic currents, HIV prevalence levels can remain high and each day the millions of young people who become sexually active join the ranks of the susceptible, underscoring the need for intensified combination prevention.