  A simple deterministic model is proposed to represent the basic aspects
concerning the effects of different antiretroviral treatment schedules on HIV
incidence and prevalence of affected populations. The model mimics current
treatment guidelines applied in Brazil. However, the model does not intend to
fit the data with any acceptable degree of accuracy since uncertainties on the
values of the parameters and on the precise effect of the treatment put some
limits on the practical implications of our model from which only orders of
magnitude and some qualitative effects can be deduced. So, this paper intends
to provide a conceptual and mechanistic understanding of the possible long term
effects of treatment on the dynamics of HIV transmission.
  According to the model, the effect of the treatment depends on the level of
sexual activity of the subpopulations considered, being more pronounced on the
subpopulations with the highest sexual activity levels. Also, inefficient
treatment can be prejudicial depending on the level of sexual activity and on
the capacity to provide adequate treatment coverages to the population
affected.
