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Serological Markers Suggest Heterogeneity of Effectiveness of Malaria Control Interventions on Bioko Island, Equatorial Guinea
Jackie Cook1, Immo Kleinschmidt2, Christopher Schwabe3, Gloria Nseng4, Teun Bousema1, Patrick H. Corran1, Eleanor M. Riley1, Chris J. Drakeley1*
1 Department of Immunology and Infection, London School of Hygiene and Tropical Medicine, London, United Kingdom, 2Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom, 3 Medicinal Care Development International, Silver Spring, Maryland, United States of America, 4 Ministry of Health and Social Welfare, Malabo, Equatorial Guinea

Abstract
Background: In order to control and eliminate malaria, areas of on-going transmission need to be identified andtargeted for malaria control interventions. Immediately following intense interventions, malaria transmission can become more heterogeneous if interventions are more successful in some areas than others. Bioko Island, Equatorial Guinea, has been subject to comprehensive malaria control interventions since 2004. This has resulted in substantial reductions in the parasite burden, although this drophas not been uniform across the island. Methods/Principal Findings: In 2008, filter paper blood samples were collected from 7387 people in a cross-sectional study incorporating 18 sentinel sites across Bioko, Equatorial Guinea. Antibodies were measured to P. falciparum Apical Membrane Antigen-1 (AMA-1) by Enzyme Linked Immunosorbent Assay (ELISA). Age-specific seropositivity rates were used toestimate seroconversion rates (SCR). Analysis indicated there had been at least a 60% decline in SCR in four out of five regions on the island. Changes in SCR showed a high degree of congruence with changes in parasite rate (PR) and with regional reductions in all cause child mortality. The mean age adjusted concentration of anti-AMA-1 antibodies was mapped to identify areas where individualantibody responses were higher than expected. This approach confirmed the North West of the island as a major focus of continuing infection and an area where control interventions need to be concentrated or re-evaluated. Conclusion/Interpretation: Both SCR and PR revealed heterogeneity in malaria transmission and demonstrated the variable effectiveness of malaria control measures. This work confirmsthe utility of serological analysis as an adjunct measure for monitoring transmission. Age-specific seroprevalence based evidence of changes in transmission over time will be of particular value when no baseline data are available. Importantly, SCR data provide additional evidence to link malaria control activities to contemporaneous reductions in all-cause child mortality.
Citation: Cook J,Kleinschmidt I, Schwabe C, Nseng G, Bousema T, et al. (2011) Serological Markers Suggest Heterogeneity of Effectiveness of Malaria Control Interventions on Bioko Island, Equatorial Guinea. PLoS ONE 6(9): e25137. doi:10.1371/journal.pone.0025137 Editor: Lorenz von Seidlein, Menzies School of Health Research, Australia Received February 4, 2011; Accepted August 26, 2011; Published September 27, 2011Copyright: ß 2011 Cook 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. Funding: The malariometric surveys and serological analysis were funded by Marathon Oil and Government of Equatorial Guinea. Addtionalfunding was provided by by a grant from the Wellcome Trust (078925). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: This research was supported with funds from the Marathon Oil Company. This does not alter the authors’ adherence to all the PLoS ONE policies on sharing data and materials. * E-mail:...
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