Studies on the Spatial Ecology of Malaria and the Impact of Mass Trapping of Anopheles Mosquitoes on Malaria Transmission in Southern Ethiopia

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Addis Ababa University


The sustainability of current indoor vector control methods is challenged by the emergence of insecticide resistance in malaria mosquito populations and the behavioural shift of vectors, resulting in increased outdoor biting activities. As a result, there is a dire need for novel vector control tools, which complement the existing strategies, particularly targeting the outdoor-active mosquitoes. Effective control of mosquitoes outdoors can be achieved through in-depth understandings of their spatial and behavioural ecology. The effect of landscape elements on the resting site selection of the outdoor Anopheles mosquito population was assessed. Fine-scale characterization of landscape factors within 10 m radius from resting clay pots was conducted and their association with the number of resting anophelines was determined. Canopy cover, distance from the nearest focal house, and land cover type significantly influenced the aggregation of resting mosquitoes. Canopy cover was the strongest predictor for both the number and presence of Anopheles mosquitoes in the clay pots. Female Anopheles were most frequently found resting in the pots placed within the banana plantations, and at sampling points that were ≥75 m from the focal house. To identify the factors underlying hotspots for higher vector densities and malaria incidence, and associated landscape features, monthly entomological monitoring, and fourstage repeated seasonal malaria prevalence surveys were conducted in two rural villages in southern Ethiopia. Moreover, characterization of the landscape features in and around every household of the study villages was conducted. Spatial analyses using Getis-Ord Gi* statistics were used to identify hotspots for malaria incidence, as well as malaria vector density and associated sporozoite prevalence. The result from the regression models revealed that household occupancy, location and housing conditions were the main iv predictors of vector density, entomological inoculation rate, and malaria incidence. The spatial analyses revealed that statistically significant hotspots for malaria vector densities and Plasmodium-infected individuals were identified at village edges. The impact of mass trapping of Anopheles mosquitoes using odour-baited traps was assessed in a controlled before-and-after study design in two rural villages of Southern Ethiopia. Baseline monthly entomological and seasonal cross-sectional malaria prevalence surveys were conducted in the two villages for a year. Then, mass trapping was implemented in one of the villages immediately before the beginning of the rainy season, while the monthly entomological monitoring and the seasonal malaria prevalence surveys continued in both villages for nine months, throughout the long and short rainy seasons. The impact of the mass trapping was then assessed by computing the relative reduction of entomological indices and malaria incidence in the intervention village in a seasonal comparison with the control village. The mass trapping resulted in a significant reduction in the population of the primary malaria vector in the area, An. arabiensis and the associated entomological indices (the human biting-, sporozoite-, and entomological inoculation rates) in the intervention compared to the control village. This resulted in a relative reduction of malaria incidence by 61 %, 44 %, and 49 % in the long rain, short rain, and dry seasons, respectively.



Exophilic, Hotspot, Malaria Incidence, Mass Trapping, Relative Reduction, Anopheles