Modelling the distribution and transmission intensity of lymphatic filariasis in sub-Saharan Africa prior to scaling up interventions: integrated use of geostatistical and mathematical modelling

Parasites & Vectors, Oct 2015

Background Lymphatic filariasis (LF) is one of the neglected tropical diseases targeted for global elimination. The ability to interrupt transmission is, partly, influenced by the underlying intensity of transmission and its geographical variation. This information can also help guide the design of targeted surveillance activities. The present study uses a combination of geostatistical and mathematical modelling to predict the prevalence and transmission intensity of LF prior to the implementation of large-scale control in sub-Saharan Africa. Methods A systematic search of the literature was undertaken to identify surveys on the prevalence of Wuchereria bancrofti microfilaraemia (mf), based on blood smears, and on the prevalence of antigenaemia, based on the use of an immuno-chromatographic card test (ICT). Using a suite of environmental and demographic data, spatiotemporal multivariate models were fitted separately for mf prevalence and ICT-based prevalence within a Bayesian framework and used to make predictions for non-sampled areas. Maps of the dominant vector species of LF were also developed. The maps of predicted prevalence and vector distribution were linked to mathematical models of the transmission dynamics of LF to infer the intensity of transmission, quantified by the basic reproductive number (R 0 ). Results The literature search identified 1267 surveys that provide suitable data on the prevalence of mf and 2817 surveys that report the prevalence of antigenaemia. Distinct spatial predictions arose from the models for mf prevalence and ICT-based prevalence, with a wider geographical distribution when using ICT-based data. The vector distribution maps demonstrated the spatial variation of LF vector species. Mathematical modelling showed that the reproduction number (R 0 ) estimates vary from 2.7 to 30, with large variations between and within regions. Conclusions LF transmission is highly heterogeneous, and the developed maps can help guide intervention, monitoring and surveillance strategies as countries progress towards LF elimination.

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Modelling the distribution and transmission intensity of lymphatic filariasis in sub-Saharan Africa prior to scaling up interventions: integrated use of geostatistical and mathematical modelling

Moraga et al. Parasites & Vectors Modelling the distribution and transmission intensity of lymphatic filariasis in sub-Saharan Africa prior to scaling up interventions: integrated use of geostatistical and mathematical modelling Paula Moraga 0 Jorge Cano 0 Rebecca F. Baggaley John O. Gyapong Sammy M. Njenga Birgit Nikolay 0 Emmanuel Davies Maria P. Rebollo Rachel L. Pullan 0 Moses J. Bockarie T. Déirdre Hollingsworth Manoj Gambhir Simon J. Brooker 0 0 Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine , London , UK Background: Lymphatic filariasis (LF) is one of the neglected tropical diseases targeted for global elimination. The ability to interrupt transmission is, partly, influenced by the underlying intensity of transmission and its geographical variation. This information can also help guide the design of targeted surveillance activities. The present study uses a combination of geostatistical and mathematical modelling to predict the prevalence and transmission intensity of LF prior to the implementation of large-scale control in sub-Saharan Africa. Methods: A systematic search of the literature was undertaken to identify surveys on the prevalence of Wuchereria bancrofti microfilaraemia (mf), based on blood smears, and on the prevalence of antigenaemia, based on the use of an immuno-chromatographic card test (ICT). Using a suite of environmental and demographic data, spatiotemporal multivariate models were fitted separately for mf prevalence and ICT-based prevalence within a Bayesian framework and used to make predictions for non-sampled areas. Maps of the dominant vector species of LF were also developed. The maps of predicted prevalence and vector distribution were linked to mathematical models of the transmission dynamics of LF to infer the intensity of transmission, quantified by the basic reproductive number (R0). Results: The literature search identified 1267 surveys that provide suitable data on the prevalence of mf and 2817 surveys that report the prevalence of antigenaemia. Distinct spatial predictions arose from the models for mf prevalence and ICT-based prevalence, with a wider geographical distribution when using ICT-based data. The vector distribution maps demonstrated the spatial variation of LF vector species. Mathematical modelling showed that the reproduction number (R0) estimates vary from 2.7 to 30, with large variations between and within regions. Conclusions: LF transmission is highly heterogeneous, and the developed maps can help guide intervention, monitoring and surveillance strategies as countries progress towards LF elimination. Lymphatic filariasis; Wuchereria bancrofti; Bayesian geostatistical modelling; Mathematical modelling; Basic reproductive number; Sub-Saharan Africa - Background Lymphatic filariasis (LF) is a mosquito-borne disease caused by the filarial worms, Wuchereria bancrofti, Brugia malayi and B. timori. Since the launch of the Global Programme to Eliminate Lymphatic Filariasis in 2000 an estimated total of 975 million people, including 198 million in sub-Saharan Africa, have benefitted from mass drug administration (MDA) programmes that deliver antifilarial drugs [1]. As a result of these efforts, it is estimated that the global prevalence of infection has decreased by 30 % and 18.2 million cases of LF morbidity have been averted [1]. At a country level, an increasing number of national LF control programmes have completed five or more rounds of MDA and, as a consequence, are conducting transmission assessment surveys (TAS) to determine whether prevalence of LF is <1 % and MDA can stop [2]. After stopping MDA, programmes will still need to conduct surveillance to ensure transmission has not re-emerged (i.e. there has been no recrudescence). This can either be achieved by periodic surveys, for example, by repeating a TAS 2–3 years after stopping MDA, or through screening of routine blood samples [3]. For the process of verification, countries will also need to conduct surveillance in areas judged to be non-endemic at the start of the programme. To help reduce costs, surveillance can be stratified according to the risk of recrudescence. This risk may be predicted from analysis of the historical, pre-intervention transmission levels, vector type and capacity and environmental and demographic factors known to influence the intrinsic sensitivity (receptivity) of transmission [4–6]. Recent work at the country level highlights the environmental, socio-demographic, and intervention drivers of LF and how this information can be used to stratify areas according to likelihood of transmission being interrupted or persisting [7–9]. Other work has used Bayesian geostatistical modelling to predict the distribution of LF at country [10] and continental [11] scales. In this paper, we use a combination of Bayesian geostatistical and mathematical modelling to develop maps of the prevalence and transmission intensity of bancroftian f (...truncated)


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Paula Moraga, Jorge Cano, Rebecca Baggaley, John Gyapong, Sammy Njenga, Birgit Nikolay, Emmanuel Davies, Maria Rebollo, Rachel Pullan, Moses Bockarie, T. Hollingsworth, Manoj Gambhir, Simon Brooker. Modelling the distribution and transmission intensity of lymphatic filariasis in sub-Saharan Africa prior to scaling up interventions: integrated use of geostatistical and mathematical modelling, Parasites & Vectors, 2015, pp. 560, 8, DOI: 10.1186/s13071-015-1166-x