Modeling the effectiveness of Esperanza Window Traps as a complementary vector control strategy for achieving the community-wide elimination of Onchocerciasis
Authors: Bilal Shakir , Smith Morgan E. , Sharma Swarnali , Zaatour Wajdi , Newcomb Ken , Unnasch Thomas R. , Michael Edwin 
Published: October 2024

Mathematical models of parasite transmission provide powerful quantitative tools for evaluating the impact of interventions for bringing about the control or elimination of community-level disease transmission. A key attribute of such tools is that they allow integration of field observations regarding the effectiveness of an intervention with the processes of parasite transmission in communities to allow the exploration of parameters connected with the optimal deployment of the intervention to meet various community-wide control or elimination goals. In this work, we analyze the effectiveness of the Esperanza Window Trap (EWT), a recently developed black fly control tool, for eliminating the transmission ofOnchocera volvulusin endemic settings by coupling seasonally-driven onchocerciasis transmission models identified for representative villages in Uganda with a landscape-level, spatially-informed model of EWT trap configurations for reducing Simulid fly populations in a given endemic setting. Our results indicate that when EWT traps are used in conjunction with MDA programs there are significant savings in the number of years needed to reach a specified set of elimination targets compared to the use of MDA alone. Adding EWT after the meeting of these thresholds and stoppage of MDA also significantly enhances the long-term sustained elimination of onchocerciasis. The number of traps required is driven by the trap black fly killing efficiency, capture range, desired coverage, inter-trap distance, size of location, and the spatial heterogeneity obtaining for the fly population in a given village/site. These findings provide important new knowledge regarding the feasibility and effectiveness of the community-wide use of EWT as a supplementary intervention alongside MDA for accelerating and sustaining the achievement of sustainable onchocerciasis elimination. Our coupling of landscape models of EWT deployment with the seasonal onchocerciasis transmission model also highlights how population-level macroparasite models may be extended effectively for modeling the effects of spatio-temporal processes on control efforts.

Author summary

While empirical studies have highlighted the effectiveness of the Esperanza Window Trap (EWT) as a potential tool for reducing biting black fly populations, information regarding how to implement these traps in the field to bring about community-wide elimination of onchocerciasis transmission is lacking. Here, we show how coupling a data-driven seasonal onchocerciasis transmission model with a landscape model of EWT trap networks can provide a flexible and powerful quantitative framework for addressing the effectiveness of deploying EWT in the field for bringing about parasite elimination in conjunction with mass drug administration (MDA). Our results demonstrate that including EWT traps with ivermectin MDA can significantly reduce timelines to reach elimination thresholds, while introducing these traps post-MDA can ensure the sustained long-term elimination of parasite transmission. The optimal trap configuration for meeting these goals will depend on the trap efficiencies for fly capture and killing, trap attractant range, field coverage, inter-trap distance, number of traps used, area of a control setting and the spatial variation observed for the density of biting black flies. This work also highlights how population-level models of macroparasite transmission dynamics could be extended successfully to effectively investigate these questions.