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. 2017 Mar;33(3):175–184. doi: 10.1016/j.pt.2016.09.004

Figure 1.

Figure 1

Schematic of the Relationship between an Individual's Course of Infection, Their Contribution to the Population Infectious Reservoir and the Impact of Treatment. Panel (A) shows a hypothetical typical course of infection for untreated and treated clinical disease (i.e., symptomatic infection) and asymptomatic infection. The black horizontal line indicates the limit of detection for microscopy (200 parasites per μL). Panel (B) combines the duration of infection with the infectivity to mosquitoes to produce a relative measure of onwards infectiousness for individuals with different types of infection and treatment based on parameter values presented in [88]. We assume individuals with untreated clinical disease are highly infectious for 25 days, followed by a period of 200 days where they have patent asymptomatic infection, then 100 days where they have subpatent asymptomatic infection. During these periods they are 65% and 9% as infectious as at their peak, respectively. Individuals with clinical disease who are treated with a non-artemisinin combination therapy (ACT) with no gametocytocidal (GX) activity (dark blue) are assumed to remain highly infectious for 25 days after treatment, whereas treatment with an ACT (medium blue) reduces the total duration to 10 days and the infectiousness after treatment to 9% of the pretreatment amount 22, 40, 88. A drug with perfect GX activity (light blue) renders individuals instantly noninfectious after treatment 22, 24, 25. Panel (C) considers the population-level contribution of untreated (red) and treated (dark blue) symptomatic and asymptomatic (orange) individuals based on the individual-level durations of infection presented in (A) and the relative onwards infectiousness presented in (B). We assume that 80% of individuals with clinical disease are treated, and that 30% of new infections are symptomatic in a high transmission setting and 60% in a low transmission setting [88]. Converting individual-level infectiousness to the population level allows us to see that treated individuals only contribute 5% or 14% (high and low transmission settings respectively) to the total infectiousness of a population. This indicates that improving the gametocytocidal activity of an antimalarial drug used for treatment of symptomatic cases can only potentially impact a small proportion of the total infectiousness of the population.