Mosquito Exposure and Malaria Morbidity: A Microlevel Analysis of Household Mosquito Populations and Malaria in a Population-Based Longitudinal Cohort in Western Kenya

• Published in: The Journal of infectious diseases 2020-03, Vol.221 (7), p.1176-1184
• Main Authors: O’Meara, Wendy Prudhomme, Simmons, Ryan, Bullins, Paige, Freedman, Betsy, Abel, Lucy, Mangeni, Judith, Taylor, Steve M, Obala, Andrew A
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Animals; Anopheles - parasitology; Child; Child, Preschool; Culicidae; Environmental Exposure - statistics & numerical data; Female; Humans; Infant; Infant, Newborn; Insecticide-Treated Bednets - statistics & numerical data; Kenya; Longitudinal Studies; Major and Brief Reports; Malaria; Malaria - epidemiology; Malaria - prevention & control; Malaria - transmission; Morbidity; Mosquito Vectors - parasitology; Mosquitoes; Young Adult
• ISSN: 0022-1899; 1537-6613
• DOI: 10.1093/infdis/jiz561

Abstract Background Malaria morbidity is highly overdispersed in the population. Fine-scale differences in mosquito exposure may partially explain this heterogeneity in individual malaria outcomes. Methods In 38 households we explored the effect of household-level mosquito exposure and individual insecticide-treated net (ITN) use on relative risk (RR) of confirmed malaria. We conducted monthly active surveillance (n = 254; 2624 person-months) and weekly mosquito collection (2092 household-days of collection), and used molecular techniques to confirm human blood feeding and exposure to infectious mosquitoes. Results Of 1494 female Anopheles (89.8% Anopheles gambiae sensu lato), 88.3% were fed, 51.9% had a human blood meal, and 9.2% were sporozoite infected. In total, 168 laboratory-confirmed malaria episodes were reported (incidence rate 0.064 episodes per person-month at risk; 95% confidence interval [CI], .055–.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. In this study, we measure the relationship between fine-scale spatiotemporal heterogeneity in exposure to infected and successfully fed malaria vectors, the incidence of malaria, and their interaction with insecticide-treated net use in a population-based cohort.