From high to low malaria transmission in Zanzibar—challenges and opportunities to achieve elimination

BACKGROUND: Substantial global progress in the control of malaria in recent years has led to increased commitment to its potential elimination. Whether this is possible in high transmission areas of sub-Saharan Africa remains unclear. Zanzibar represents a unique case study of such attempt, where mo...

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Autores principales: Björkman, A., Shakely, D., Ali, A. S., Morris, U., Mkali, H., Abbas, A. K., Al-Mafazy, A-W, Haji, K. A., Mcha, J., Omar, R., Cook, J., Elfving, K., Petzold, M., Sachs, M. C., Aydin-Schmidt, B., Drakeley, C., Msellem, M., Mårtensson, A.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BioMed Central 2019
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6341737/
https://www.ncbi.nlm.nih.gov/pubmed/30665398
http://dx.doi.org/10.1186/s12916-018-1243-z
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author Björkman, A.
Shakely, D.
Ali, A. S.
Morris, U.
Mkali, H.
Abbas, A. K.
Al-Mafazy, A-W
Haji, K. A.
Mcha, J.
Omar, R.
Cook, J.
Elfving, K.
Petzold, M.
Sachs, M. C.
Aydin-Schmidt, B.
Drakeley, C.
Msellem, M.
Mårtensson, A.
author_facet Björkman, A.
Shakely, D.
Ali, A. S.
Morris, U.
Mkali, H.
Abbas, A. K.
Al-Mafazy, A-W
Haji, K. A.
Mcha, J.
Omar, R.
Cook, J.
Elfving, K.
Petzold, M.
Sachs, M. C.
Aydin-Schmidt, B.
Drakeley, C.
Msellem, M.
Mårtensson, A.
author_sort Björkman, A.
collection PubMed
description BACKGROUND: Substantial global progress in the control of malaria in recent years has led to increased commitment to its potential elimination. Whether this is possible in high transmission areas of sub-Saharan Africa remains unclear. Zanzibar represents a unique case study of such attempt, where modern tools and strategies for malaria treatment and vector control have been deployed since 2003. METHODS: We have studied temporal trends of comprehensive malariometric indices in two districts with over 100,000 inhabitants each. The analyses included triangulation of data from annual community-based cross-sectional surveys, health management information systems, vital registry and entomological sentinel surveys. RESULTS: The interventions, with sustained high-community uptake, were temporally associated with a major malaria decline, most pronounced between 2004 and 2007 and followed by a sustained state of low transmission. In 2015, the Plasmodium falciparum community prevalence of 0.43% (95% CI 0.23–0.73) by microscopy or rapid diagnostic test represented 96% reduction compared with that in 2003. The P. falciparum and P. malariae prevalence by PCR was 1.8% (95% CI 1.3–2.3), and the annual P. falciparum incidence was estimated to 8 infections including 2.8 clinical episodes per 1000 inhabitants. The total parasite load decreased over 1000-fold (99.9%) between 2003 and 2015. The incidence of symptomatic malaria at health facilities decreased by 94% with a trend towards relatively higher incidence in age groups > 5 years, a more pronounced seasonality and with reported travel history to/from Tanzania mainland as a higher risk factor. All-cause mortality among children < 5 years decreased by 72% between 2002 and 2007 mainly following the introduction of artemisinin-based combination therapies whereas the main reduction in malaria incidence followed upon the vector control interventions from 2006. Human biting rates decreased by 98% with a major shift towards outdoor biting by Anopheles arabiensis. CONCLUSIONS: Zanzibar provides new evidence of the feasibility of reaching uniquely significant and sustainable malaria reduction (pre-elimination) in a previously high endemic region in sub-Saharan Africa. The data highlight constraints of optimistic prognostic modelling studies. New challenges, mainly with outdoor transmission, a large asymptomatic parasite reservoir and imported infections, require novel tools and reoriented strategies to prevent a rebound effect and achieve elimination. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12916-018-1243-z) contains supplementary material, which is available to authorized users.
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spelling pubmed-63417372019-01-24 From high to low malaria transmission in Zanzibar—challenges and opportunities to achieve elimination Björkman, A. Shakely, D. Ali, A. S. Morris, U. Mkali, H. Abbas, A. K. Al-Mafazy, A-W Haji, K. A. Mcha, J. Omar, R. Cook, J. Elfving, K. Petzold, M. Sachs, M. C. Aydin-Schmidt, B. Drakeley, C. Msellem, M. Mårtensson, A. BMC Med Research Article BACKGROUND: Substantial global progress in the control of malaria in recent years has led to increased commitment to its potential elimination. Whether this is possible in high transmission areas of sub-Saharan Africa remains unclear. Zanzibar represents a unique case study of such attempt, where modern tools and strategies for malaria treatment and vector control have been deployed since 2003. METHODS: We have studied temporal trends of comprehensive malariometric indices in two districts with over 100,000 inhabitants each. The analyses included triangulation of data from annual community-based cross-sectional surveys, health management information systems, vital registry and entomological sentinel surveys. RESULTS: The interventions, with sustained high-community uptake, were temporally associated with a major malaria decline, most pronounced between 2004 and 2007 and followed by a sustained state of low transmission. In 2015, the Plasmodium falciparum community prevalence of 0.43% (95% CI 0.23–0.73) by microscopy or rapid diagnostic test represented 96% reduction compared with that in 2003. The P. falciparum and P. malariae prevalence by PCR was 1.8% (95% CI 1.3–2.3), and the annual P. falciparum incidence was estimated to 8 infections including 2.8 clinical episodes per 1000 inhabitants. The total parasite load decreased over 1000-fold (99.9%) between 2003 and 2015. The incidence of symptomatic malaria at health facilities decreased by 94% with a trend towards relatively higher incidence in age groups > 5 years, a more pronounced seasonality and with reported travel history to/from Tanzania mainland as a higher risk factor. All-cause mortality among children < 5 years decreased by 72% between 2002 and 2007 mainly following the introduction of artemisinin-based combination therapies whereas the main reduction in malaria incidence followed upon the vector control interventions from 2006. Human biting rates decreased by 98% with a major shift towards outdoor biting by Anopheles arabiensis. CONCLUSIONS: Zanzibar provides new evidence of the feasibility of reaching uniquely significant and sustainable malaria reduction (pre-elimination) in a previously high endemic region in sub-Saharan Africa. The data highlight constraints of optimistic prognostic modelling studies. New challenges, mainly with outdoor transmission, a large asymptomatic parasite reservoir and imported infections, require novel tools and reoriented strategies to prevent a rebound effect and achieve elimination. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12916-018-1243-z) contains supplementary material, which is available to authorized users. BioMed Central 2019-01-22 /pmc/articles/PMC6341737/ /pubmed/30665398 http://dx.doi.org/10.1186/s12916-018-1243-z Text en © The Author(s). 2019 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
spellingShingle Research Article
Björkman, A.
Shakely, D.
Ali, A. S.
Morris, U.
Mkali, H.
Abbas, A. K.
Al-Mafazy, A-W
Haji, K. A.
Mcha, J.
Omar, R.
Cook, J.
Elfving, K.
Petzold, M.
Sachs, M. C.
Aydin-Schmidt, B.
Drakeley, C.
Msellem, M.
Mårtensson, A.
From high to low malaria transmission in Zanzibar—challenges and opportunities to achieve elimination
title From high to low malaria transmission in Zanzibar—challenges and opportunities to achieve elimination
title_full From high to low malaria transmission in Zanzibar—challenges and opportunities to achieve elimination
title_fullStr From high to low malaria transmission in Zanzibar—challenges and opportunities to achieve elimination
title_full_unstemmed From high to low malaria transmission in Zanzibar—challenges and opportunities to achieve elimination
title_short From high to low malaria transmission in Zanzibar—challenges and opportunities to achieve elimination
title_sort from high to low malaria transmission in zanzibar—challenges and opportunities to achieve elimination
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6341737/
https://www.ncbi.nlm.nih.gov/pubmed/30665398
http://dx.doi.org/10.1186/s12916-018-1243-z
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