Mosquito exposure and malaria morbidity; a micro-level analysis of household mosquito populations and malaria in a population-based longitudinal cohort in western Kenya

Background Malaria morbidity is highly overdispersed in the population. Fine-scale differences in mosquito exposure may partially explain this heterogeneity. However, exposure variability has not been related to individual malaria outcomes. Methods We established a cohort of 38 households to explore the effect of household-level mosquito exposure and individual insecticide treated net(ITN) use on relative risk(RR) of diagnostically-confirmed malaria. We conducted monthly active surveillance (n=254; 2,624 person-months) and weekly mosquito collection in all households (2,092 household-days of collection). We used molecular techniques to confirm human blood feeding and exposure to infectious mosquitoes. Results Of 1,494 female anopheles (89.8% Anopheles gambiae s . l .). 88.3% were fed, 51.9% had a human bloodmeal, and 9.2% were sporozoite-infected. 168 laboratory-confirmed malaria episodes were reported (incidence rate 0.064 episodes per person-month at risk, 95% confidence interval [CI]:0.055,0.074). Malaria risk was directly associated with exposure to sporozoite-infected mosquitoes (RR=1.24, 95%CI:1.11,1.38). No direct effect was measured between ITN use and malaria morbidity, however, ITN use did moderate the effect of mosquito exposure on morbidity. Conclusions Malaria risk increases linearly with vector density and feeding success for persons with low ITN use. In contrast, malaria risk among high ITN users is consistently low and insensitive to variation in mosquito exposure. Summary In this study, we measure the relationship between fine-scale spatio-temporal heterogeneity in exposure to infected and successfully-fed malaria vectors, the incidence of malaria, and their interaction with ITN use in a population-based cohort. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Research reported in this publication was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under Award Number R21AI126024. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health ### Author Declarations All relevant ethical guidelines have been followed and any necessary IRB and/or ethics committee approvals have been obtained. Yes All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes Any clinical trials involved have been registered with an ICMJE-approved registry such as ClinicalTrials.gov and the trial ID is included in the manuscript. Not Applicable I have followed all appropriate research reporting guidelines and uploaded the relevant Equator, ICMJE or other checklist(s) as supplementary files, if applicable. Yes Data will be available upon final publication of the peer-reviewed version of the manuscript