Figure 1

SIS two-stage model. Susceptible individuals (S) become infected (I) with wild-type infections at the rate h _w (1-ξ _i ) and resistant infections at the rate h _x , where h _i is the happenings rate (see text) and ξ _i is the rate at which new infections result in clinically manifested symptoms that are treated and resolved prior to the formation of gametocytes. Infected individuals naturally clear resistant infections at rate r _xi , and they clear wild-type infections at the rate ρ _i +r _wi , where ρ _i is the rate of drug treatment. Infected individuals acquire semi-immunity at rate θ and lose immunity at rate γ if they are no longer infected. Individuals die from all states at a background rate of μ and are born at rate B as nonimmune susceptibles (process not shown).