Hitting Hotspots: Spatial Targeting of Malaria for Control and Elimination

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Teun Bousema and colleagues argue that targeting malaria “hotspots” is a highly efficient way to reduce malaria transmission at all levels of transmission intensity.

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Increased proportions of outdoor feeding among residual malaria vector populations following increased use of insecticide-treated nets in rural Tanzania

Tanya Russell, Nicodem Govella, Salum Azizi … (2011)

Background Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) represent the front-line tools for malaria vector control globally, but are optimally effective where the majority of baseline transmission occurs indoors. In the surveyed area of rural southern Tanzania, bed net use steadily increased over the last decade, reducing malaria transmission intensity by 94%. Methods Starting before bed nets were introduced (1997), and then after two milestones of net use had been reached-75% community-wide use of untreated nets (2004) and then 47% use of ITNs (2009)-hourly biting rates of malaria vectors from the Anopheles gambiae complex and Anopheles funestus group were surveyed. Results In 1997, An. gambiae s.l. and An. funestus mosquitoes exhibited a tendency to bite humans inside houses late at night. For An. gambiae s.l., by 2009, nocturnal activity was less (p = 0.0018). At this time, the sibling species composition of the complex had shifted from predominantly An. gambiae s.s. to predominantly An. arabiensis. For An. funestus, by 2009, nocturnal activity was less (p = 0.0054) as well as the proportion biting indoors (p < 0.0001). At this time, An. funestus s.s. remained the predominant species within this group. As a consequence of these altered feeding patterns, the proportion (mean ± standard error) of human contact with mosquitoes (bites per person per night) occurring indoors dropped from 0.99 ± 0.002 in 1997 to 0.82 ± 0.008 in 2009 for the An. gambiae complex (p = 0.0143) and from 1.00 ± <0.001 to only 0.50 ± 0.048 for the An. funestus complex (p = 0.0004) over the same time period. Conclusions High usage of ITNs can dramatically alter African vector populations so that intense, predominantly indoor transmission is replaced by greatly lowered residual transmission, a greater proportion of which occurs outdoors. Regardless of the underlying mechanism, the residual, self-sustaining transmission will respond poorly to further insecticidal measures within houses. Additional vector control tools which target outdoor biting mosquitoes at the adult or immature stages are required to complement ITNs and IRS.

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Epidemiology and infectivity of Plasmodium falciparum and Plasmodium vivax gametocytes in relation to malaria control and elimination.

Teun Bousema, Chris Drakeley (2011)

Malaria remains a major cause of morbidity and mortality in the tropics, with Plasmodium falciparum responsible for the majority of the disease burden and P. vivax being the geographically most widely distributed cause of malaria. Gametocytes are the sexual-stage parasites that infect Anopheles mosquitoes and mediate the onward transmission of the disease. Gametocytes are poorly studied despite this crucial role, but with a recent resurgence of interest in malaria elimination, the study of gametocytes is in vogue. This review highlights the current state of knowledge with regard to the development and longevity of P. falciparum and P. vivax gametocytes in the human host and the factors influencing their distribution within endemic populations. The evidence for immune responses, antimalarial drugs, and drug resistance influencing infectiousness to mosquitoes is reviewed. We discuss how the application of molecular techniques has led to the identification of submicroscopic gametocyte carriage and to a reassessment of the human infectious reservoir. These components are drawn together to show how control measures that aim to reduce malaria transmission, such as mass drug administration and a transmission-blocking vaccine, might better be deployed.

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Heterogeneities in the transmission of infectious agents: implications for the design of control programs.

M. E. Woolhouse, C. Dye, J F Etard … (1997)

From an analysis of the distributions of measures of transmission rates among hosts, we identify an empirical relationship suggesting that, typically, 20% of the host population contributes at least 80% of the net transmission potential, as measured by the basic reproduction number, R0. This is an example of a statistical pattern known as the 20/80 rule. The rule applies to a variety of disease systems, including vector-borne parasites and sexually transmitted pathogens. The rule implies that control programs targeted at the "core" 20% group are potentially highly effective and, conversely, that programs that fail to reach all of this group will be much less effective than expected in reducing levels of infection in the population as a whole.

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Journal

Journal ID (nlm-ta): PLoS Med

Journal ID (publisher-id): PLoS

Journal ID (pmc): plosmed

Title: PLoS Medicine

Publisher: Public Library of Science (San Francisco, USA )

ISSN (Print): 1549-1277

ISSN (Electronic): 1549-1676

Publication date Collection: January 2012

Publication date (Print): January 2012

Publication date (Electronic): 31 January 2012

Volume: 9

Issue: 1

Electronic Location Identifier: e1001165

Affiliations

[1 ]Department of Immunity and Infection, London School of Hygiene & Tropical Medicine, London, United Kingdom

[2 ]Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands

[3 ]Department of Epidemiology, Biostatistics, and HTA, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands

[4 ]Department of Infectious Disease Epidemiology, MRC Centre for Outbreak Analysis and Modeling, Imperial College London, London, United Kingdom

[5 ]Johns Hopkins Malaria Research Institute and Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America

[6 ]Laboratory of Entomology, Wageningen University and Research Centre, Wageningen, The Netherlands

[7 ]Global Health Group, University of California, San Francisco, San Francisco, California, United States of America

Author notes

* E-mail: teun.bousema@ 123456lshtm.ac.uk

Conceived and designed the experiments: TB JTG CD RG. Performed the experiments: TB JTG TSC. Analyzed the data: TB JTG TSC DLS AG. Contributed reagents/materials/analysis tools: JTG TSC AG. Wrote the first draft of the manuscript: TB CD RG. Contributed to the writing of the manuscript: TB JTG RWS DLS TSC WT AG CD RG. ICMJE criteria for authorship read and met: TB JTG RWS DLS TSC WT AG CD RG. Agree with manuscript results and conclusions: TB JTG RWS DLS TSC WT AG CD RG.

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Publisher ID: PMEDICINE-D-11-02340

DOI: 10.1371/journal.pmed.1001165

PMC ID: 3269430

PubMed ID: 22303287

SO-VID: 84df18e4-c32b-493f-92f3-53b54c81ce08

Copyright © Bousema et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Hitting Hotspots: Spatial Targeting of Malaria for Control and Elimination

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Abstract

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Malaria vaccine development

Most cited references 52

Increased proportions of outdoor feeding among residual malaria vector populations following increased use of insecticide-treated nets in rural Tanzania

Epidemiology and infectivity of Plasmodium falciparum and Plasmodium vivax gametocytes in relation to malaria control and elimination.

Heterogeneities in the transmission of infectious agents: implications for the design of control programs.

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