Real-World Impact of Next Generation Insecticidal Nets for Malaria Control in Rural Western Kenya

PROJECT SUMMARY Long-lasting Insecticidal Nets (LLINs) have been associated with declining malaria infections in Sub-Saharan Africa, but recently several threats have emerged that may be undermining their continued efficacy. These include emerging insecticide resistance, human behavior such as inconsistent use, and possible changes in mosquito behavior. Among these three, attention has primarily been focused on insecticide resistance. To mitigate against resistance, LLINs have been modified to include an insecticide coupled with a synergist (piperonyl butoxide, PBO) which restores metabolic sensitivity in otherwise resistant vectors. In mid-2021, PBO LLINs were distributed in a pilot program in three counties in Kenya, including within our existing longitudinal cohort in Bungoma County. Preliminary data from our cohort indicates high initial uptake followed by a sharp decline in use. Initial feedback from the community points towards some concerns with these PBO-LLINs. The objective of the proposed work is to study the efficacy decay of the PBO-LLINs in an implementation phase over a period of five years. We will leverage our long-standing community-based cohort of more than 500 people which includes monthly active- and passively-detected cases of malaria, weekly collections of vectors, and monthly surveys of bednet use and quality. Given the rich longitudinal data pre- and post-adoption of PBO-LLINs and the close engagement with community participants, our study offers an important setting in which to understand the human, entomological, and parasitologic impacts of these bednets in African settings. In Aim 1, we describe changes in ITN use over time, including pre-and post-PBO LLIN distribution, coupled with qualitative data collection to further explore contextual and human behavioral factors affecting ITN utilization. We will also monitor PBO-LLIN integrity and bioefficacy over time. In Aim 2, we will quantify changes in malaria vector populations before and after PBO-LLINs, including species distribution, feeding success, and insecticide resistance, using an archive of more than 5,000 female anopheles’ samples. To understand aspects of mosquito behavior that impact the effectiveness of PBO nets, we will target exophilic/exophagic vectors using outdoor trapping techniques. To monitor for emergence of resistance to the PBO synergist, we will conduct standardized phenotypic assays using field caught mosquitoes. In Aim 3, we will correlate individual and household-level differences in malaria infection and disease with coverage and use of conventional LLINs vs PBO-LLINs. Generalized linear models that incorporate the longitudinal structure of the data will be used to elucidate how the complex relationship between malaria and type of net is affected by vector abundance, vector species, insecticide resistance and human behavior. This study will generate evidence on contextual factors contributing to PBO LLIN efficacy decay and correlate this with both parasitological and entomological indicators. This could inform co-interventions that will maximize benefits from the next generation LLINs.