Spatial Epidemiological Approaches for the Control of Infection and Morbidity Associated with Neglected Tropical Diseases in sub-Saharan Africa

Soares Magalhaes, Ricardo (2011). Spatial Epidemiological Approaches for the Control of Infection and Morbidity Associated with Neglected Tropical Diseases in sub-Saharan Africa PhD Thesis, School of Population Health, The University of Queensland.

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Author Soares Magalhaes, Ricardo
Thesis Title Spatial Epidemiological Approaches for the Control of Infection and Morbidity Associated with Neglected Tropical Diseases in sub-Saharan Africa
School, Centre or Institute School of Population Health
Institution The University of Queensland
Publication date 2011-12-01
Thesis type PhD Thesis
Supervisor Archie Clements
Simon Brooker
Total pages 300
Total colour pages 100
Total black and white pages 200
Language eng
Subjects 010402 Biostatistics
111706 Epidemiology
Abstract/Summary Background: Funding agencies are dedicating substantial resources to tackling helminth infections. Recently there has been increased advocacy for an integrated approach to control which can be guided by maps that show the co-distribution of multiple parasite infections. The socioeconomic environment, which impacts on the availability of water supply, sanitation and hygiene (WASH), is an important determinant of helminth infection and recent studies have shown substantial regional disparities in WASH. Morbidity associated with helminth infections includes iron-deficiency anaemia, reduced growth and impaired cognition and is marked in those with intense infections (high worm burden) and coinfections (infections with multiple parasite species). However, helminth prevalence, infection intensity and coinfections are indirect indicators of morbidity. Anaemia is the most well-studied morbidity outcome of helminth infections and measures of anaemia are often used as direct indicators of the success of helminth control programmes. Aims: The aims were, using spatial prediction methods in selected African countries, 1) to produce helminth coendemicity maps to guide integrated anthelminth therapy for schistosomiasis and soil-transmitted helminthiasis (STH); 2) quantify the role of WASH in the risk of schistosomiasis and STH ; 3) identify communities at highest risk of helminth morbidity and transmission; 4) estimate the spatial variability of anaemia in children aged 1–4 y (preschool children); 5) and, quantify the risk of anaemia in preschool children attributable to malnutrition, malaria, and helminth infections. Methods: The first helminth coendemicity map for Sierra Leone (SL) was generated using data collected in different surveys during 2008 and 2010. This involved predicting S. haematobium prevalence using model-based geostatistics (MBG); generating a combined map of schistosomiasis using S. mansoni predictions within a novel probabilistic model; and overlaying this map with a predictive prevalence map of hookworm in a geographical information system (GIS). I quantified the role of WASH as a driver of helminth risk using Demographic Health Survey (DHS) data on WASH from Burkina Faso, Ghana and Mali. This involved generating spatial predictions of WASH indicators across the region; using those predictions as covariates in MBG models for schistosomiasis and hookworm; and estimation of the population attributable fraction (PAF) of helminth risk that could be averted by improving WASH. The identification of communities at highest risk of helminth morbidity and transmission was possible using S. haematobium and hookworm data from Ghana. This involved developing MBG models of coinfection and helminth infection intensity and overlaying the intensity maps in a GIS. I then investigated spatial variation in preschool anaemia risk at the continental level in SSA and the role of malnutrition and parasite infections of preschool age anaemia in West Africa using environmental variables, DHS haemoglobin concentration (Hb) and malnutrition data, predicted Plasmodium falciparum parasite rate in the 2- to 10-y age group (Pf PR2–10) generated by the Malaria Atlas project and predicted prevalence of S. haematobium and hookworm infections which I had created using helminth survey data. Results: Using a combined schistosomiasis risk map and a co-endemicity map for SL, I identified high-risk communities for schistosomiasis infection in the north-eastern half of the country and predicted that 825,871 school-age children require annual treatment with praziquantel, 57% (466,575) of which also require annual treatment with albendazole. For West Africa, I estimated attributable fractions of water supply for S. mansoni and S. haematobium to be 47% and 71% respectively. The PAF of natural floor type was 21% for S. haematobium, 16% for S. mansoni and 86% for hookworm. Using coinfection and co-intensity maps in Ghana, I identified communities around Lake Volta at increased risk of severe morbidity and environmental contamination. In my assessment of spatial variation of preschool age anaemia in SSA, I found significant continent-wide associations between Hb and environmental variables, particularly in West Africa. Also in West Africa, I estimated that 36.8%, 14.9%, 3.7%, 4.2%, and 0.9% of anaemia cases could be averted by eliminating malnutrition, malaria, S. haematobium infections, hookworm infections, and S. haematobium/hookworm coinfections, respectively. Conclusions: In this thesis I present a novel mapping approach to coendemicity mapping that can help identify communities in which to integrate anthelminthic therapy. This thesis demonstrates that WASH plays a substantial role in helminth infections of school-age children and identify communities where anthelminthic therapy integrated with interventions to improve WASH will yield the greatest health benefits. In addition, it shows that combining intensity maps of two or more parasites can help identify communities in which to integrate anthelminthic therapy with the aim of reducing morbidity and helminth transmission. The research in this thesis demonstrates that preschool anaemia burden in SSA is spatially variable and associated with environmental drivers of known contributors. It shows that malnutrition, malaria and helminth infections play an important role in preschool anaemia and that anaemia maps adjusted for malnutrition and infectious contributors (such as malaria and helminths) can help identify communities in which to integrate not only anthelminthic therapy but other interventions aimed at other infections and nutritional contributors.
Keyword public health
disease control
Spatial analysis
Helminth Infection
sub-Saharan Africa
Additional Notes 22-24, 103, 107, 111, 114, 116, 129-134, 137-149, 154-163, 165-180, 197-227, 235-243, 249-253, 264, 265

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Created: Tue, 19 Jun 2012, 19:56:25 EST by Ricardo Soares Magalhaes on behalf of Library - Information Access Service