Targeting Asymptomatic Malaria Infections: Active Surveillance in Control and Elimination

PLoS Medicine, Jun 2013

Hugh Sturrock and colleagues discuss the role of active case detection in low malaria transmission settings. They argue that the evidence for its effectiveness is sparse and that targeted mass drug administration should be evaluated as an alternative or addition to active case detection. Please see later in the article for the Editors' Summary

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Targeting Asymptomatic Malaria Infections: Active Surveillance in Control and Elimination

et al. (2013) Targeting Asymptomatic Malaria Infections: Active Surveillance in Control and Elimination. PLoS Med 10(6): e1001467. doi:10.1371/ journal.pmed.1001467 Targeting Asymptomatic Malaria Infections: Active Surveillance in Control and Elimination Hugh J. W. Sturrock 1 2 Michelle S. Hsiang 1 2 Justin M. Cohen 1 2 David L. Smith 1 2 Bryan Greenhouse 1 2 Teun Bousema 1 2 Roly D. Gosling 1 2 0 AI089674]. TB is supported by a Grand Challenge Grant of the Bill & Melinda Gates Foundation (No. OPP1024438). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript 1 Funding: HJWS and RDG are supported by a grant from the Bill & Melinda Gates Foundation [ 2 1 Malaria Elimination Initiative, Global Health Group, University of California, San Francisco, United States of America, 2 Department of Pediatrics, University of California, San Francisco, United States of America , 3 Clinton Health Access Initiative, Boston, MA , United States of America, 4 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, United States of America, 5 Department of Medicine, University of California, San Francisco, United States of America, 6 Department of Immunology and Infection, London School of Hygiene and Tropical Medicine , London , United Kingdom , 7 Department of Medical Microbiology, Radboud University Nijmegen Medical Centre , Nijmegen , The Netherlands - The scale-up of interventions has reduced malaria burden and transmission across a number of countries [13]. As transmission declines, it often becomes increasingly focal [4], and programs need to adapt and target the remaining parasite reservoirs, deploying resources with increasing granularity. At very low transmission intensity, elimination of malaria may involve finding and treating individual infections. At large spatial scales, infections tend to cluster into foci related to environmental, climatic, and ecological suitability for vectors and transmission [5]. At smaller scales within these foci, hotspots, which consist of a household or groups of households, maintain higher transmission of malaria and a consistent reservoir of parasites throughout the year [4,68] (Figure 1, Box 1). Infections are also clustered in certain demographic hot populations, or hotpops, associated with demographic risk factors for transmission [911] (Figure 2, Box 1). In low transmission or elimination settings, strategies for detecting and targeting these clusters of infection, whether geographic or demographic, become important strategies to reduce the local parasite reservoir and interrupt transmission [12]. All malaria control programs have passive surveillance systems that, to greater or lesser degrees, identify, treat, and report individuals with malaria who present to health facilities. While useful for intelligence gathering, passive surveillance alone has a limited impact on malaria transmission as only symptomatic patients The Policy Forum allows health policy makers around the world to discuss challenges and opportunities for improving health care in their societies. receive treatment when they seek medical care. It is well known, however, that whether transmission is low or high, the majority of infections, including carriers of gametocytes (the life parasite stage responsible for onward transmission to mosquitoes), are asymptomatic [1318]. To overcome the inherent limitations of passive surveillance and to target the asymptomatic parasite pool, as well as symptomatic infections in individuals who do not or cannot seek treatment, a number of programs have adopted active case detection (ACD) strategies [12]. Despite its increasing popularity across a number of countries, and recommendation by the World Health Organization (WHO) for use in malaria elimination [12], the diversity of ACD methods and the relative strengths and weaknesses of the various approaches are poorly described. In this Policy Forum, we discuss the potential role of ACD in malaria control and elimination. While we focus on P. falciparum, the discussion also includes the potential role of ACD in the control and elimination of P. vivax. Active Case Detection Methods ACD for malaria infection has a variety of definitions and designs [19]. The WHO recently revised the definition of ACD [12] (Box 2) to differentiate methods that test only febrile individuals (fever screening) from those that target all individuals (active infection detection, aggressive active case detection, or mass screen and treat) [14,20,21]. While requiring more resources, approaches that target all people at risk of infection enable the targeting of the asymptomatic parasite pool. For the remainder of this discussion we use the term ACD to refer to the active detection of malaria infections in both symptomatically and asymptomatically infected individuals. Competing Interests: The authors have declared that no competing interests exist. (...truncated)


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Hugh J. W. Sturrock, Michelle S. Hsiang, Justin M. Cohen, David L. Smith, Bryan Greenhouse, Teun Bousema, Roly D. Gosling. Targeting Asymptomatic Malaria Infections: Active Surveillance in Control and Elimination, PLoS Medicine, 2013, 6, DOI: 10.1371/journal.pmed.1001467