Modelling the Expansion of the Highly Active Anti-retroviral Therapy for HIV, within Risk Behaviour Environment

One of the key contributors to the spread of the HIV epidemic is the prevalence of risk behaviour, such as unprotected sexual contact and the sharing of infected hypodermic syringes, within the susceptible population. We assume that risk behaviour is a social phenomenon and that the propensity of any given individual to engage in such behaviour depends on the norms within their social environment. The likelihood of any given susceptible individual engaging in risky behaviour then becomes a function of the prevalence of risk behaviour in their immediate social group. In this view, behavioural interventions could target either the frequency and intensity of risk behaviour (harm reduction strategies) or the ability of those engaging in risk behaviour to recruit others (education and risk awareness campaigns).

Another important factor influencing HIV epidemics (particularly in rich countries) is the increased use of Highly Active Antiretroviral Therapy (HAART), which both prolongs the healthy life of the treated individual and dramatically reduces their infectiousness. Presence of HAART program can impact the risk-behavioural patterns in a variety of ways - not least by "normalizing" the risky behaviour by reducing apparent treat of HIV (in so-called "HAART optimism"). Our model studies the interplay between HAART and various behavioural interventions and their combined impact on the spread of HIV in the population.