Behaviour change and treatment of core groups: its effect on the spread of HIV/AIDS.

A general model is considered for treatment and behaviour change of the Human Immunodeficiency Virus (HIV) infected in a highly sexually active core group of female commercial sex workers (CSWs) and a 'bridge population' of young unpartnered males. In this model, the spread of HIV/AIDS in the community is carried out mainly through the sexual interaction between the core group and the bridge population which acts as a bridge for the spread of disease to the general population. We will consider the effect of treatment of the infected and/or the subsequent behaviour change when targeted toward the core group and the bridge population. Analytical results will be given for a strategy which targets treatment and behaviour change at either the core group or the bridge population. Numerical examples are also provided to illustrate the biological significance of the treatment/behaviour change and its effect on the threshold parameter values. The results show that if the contact rates and transmission probabilities of the treated individuals are sufficiently reduced, the treatment/behaviour change can eradicate the disease provided that the level of treatment in the infected population is sufficiently high. However, an ill-planned treatment program which fails to meet the required reductions in contact rate or transmission probability could have a detrimental effect on the spread of the epidemic.