Evaluation of the effectiveness of mass drug administration strategies for reducing scabies burden in Monrovia, Liberia: An agent-based modelling approach

Background Scabies is a parasitic infestation with high global burden. Mass drug administrations (MDAs) are recommended for communities with a scabies prevalence of >10%. Quantitative analyses are needed to demonstrate the likely effectiveness of MDA recommendations. In this study, we compare the effectiveness of differing MDA strategies, supported by improved treatment access, on scabies prevalence in Monrovia, Liberia. Methods We developed an agent-based model of scabies transmission calibrated to demographic and epidemiological data from Monrovia. We used this model to compare the effectiveness of MDA scenarios for achieving scabies elimination and reducing scabies burden, as measured by time until recrudescence following delivery of an MDA and disability-adjusted-life-years (DALYs) averted. We also investigated the additional impact of improving access to scabies treatment following delivery of an MDA. Results Our model showed that 3 rounds of MDA delivered at 6-month intervals and reaching 80% of the population could reduce prevalence below 2% for 3 years following the final round, before recrudescence. When MDAs were followed by increased treatment uptake, prevalence was maintained below 2% indefinitely. Increasing the number of and coverage of MDA rounds increased the probability of achieving elimination and the DALYs averted. Conclusions Our results suggest that acute reduction of scabies prevalence by MDA can support a transition to improved treatment access. This study demonstrates how modelling can be used to estimate the expected impact of MDAs by projecting future epidemiological dynamics and health gains under alternative scenarios. Summary We use an agent-based model to demonstrate that mass drug administration (MDA) programs can achieve sustained reduction in scabies prevalence. However, effective MDAs must be accompanied by systemic changes that increase the rate of scabies treatment to prevent recrudescence.