Heterogeneity and Changes in Inequality of Malaria Risk after Introduction of Insecticide-Treated Bed Nets in Macha, Zambia

Laura C. Norris W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland

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Douglas E. Norris W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland

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In 2007, the first free mass distribution of insecticide-treated bed nets (ITNs) occurred in southern Zambia. To determine the effect of ITNs on heterogeneity in biting rates, human DNA from Anopheles arabiensis blood meals was genotyped to determine the number of hosts that had contributed to the blood meals. The multiple feeding rate decreased from 18.9% pre-ITN to 9.1% post-ITN, suggesting that mosquito biting had focused onto a smaller fraction of the population. Pre-ITN, 20% of persons in a household provided 40% of blood meals, which increased to 59% post-ITN. To measure heterogeneity over a larger scale, mosquitoes were collected in 90 households in two village areas. Of these households, 25% contributed 78.1% of An. arabiensis, and households with high frequencies of An. arabiensis were significantly spatially clustered. The results indicate that substantial heterogeneity in malaria risk exists at local and household levels, and household-level heterogeneity may be influenced by interventions, such as ITNs.

Author Notes

* Address correspondence to Laura C. Norris, W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins School of Public Health, 615 North Wolfe Street, Baltimore, MD 21205. E-mail: lcnorris@ucdavis.edu

Financial support: This study was supported by a National Institutes of Health Training Grant (T32 AI 007417) to Laura C. Norris, research support to Douglas E. Norris from the National Institutes of Health (International Centers of Excellence for Malaria Research) (U19 AI089680) and the Johns Hopkins Malaria Research Institute, and additional training support from the Fogarty International Center (D43 TW001587).

Authors' addresses: Laura C. Norris and Douglas E. Norris, W. Harry Feinstone Department of Molecular Microbiology and Immunology, The Johns Hopkins School of Public Health, Baltimore, MD, E-mails: lcnorris@ucdavis.edu and dnorris@jhsph.edu.

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