Evaluating survey designs for targeting preventive chemotherapy against Schistosoma haematobium and Schistosoma mansoni across Sub-Saharan Africa: a geostatistical analysis and modelling study

Abstract Background Schistosomiasis control programmes primarily use school-based surveys to identify areas for mass drug administration of preventive chemotherapy. However, as the spatial distribution of schistosomiasis can be highly focal, transmission may not be detected by surveys implemented at districts or larger spatial units. Improved mapping strategies are required to accurately and cost effectively target preventive chemotherapy to remaining foci across all possible spatial distributions of schistosomiasis. Methods Here, we use geostatistical models to quantify the spatial heterogeneity of Schistosoma haematobium and S. mansoni across Sub-Saharan Africa using the most comprehensive dataset available on school-based surveys. Applying this information to parameterise simulations, we assess the accuracy and cost of targeting alternative implementation unit sizes across the range of plausible schistosomiasis distributions. We evaluate the consequences of decisions based on survey designs implemented at district and subdistrict levels sampling different numbers of schools. Cost data was obtained from field surveys conducted across multiple countries and years, with cost effectiveness evaluated as the cost per correctly identified school. Results Models identified marked differences in prevalence and spatial distributions between countries and species; however, results suggest implementing surveys at subdistrict level increase the accuracy of treatment classifications across most scenarios. While intensively at subdistrict level resulted in the highest classification accuracy, this sampling strategy resulted in the highest costs. Alternatively, sampling the same numbers of schools currently recommended at district levels but stratifying by subdistrict increased cost effectiveness. Conclusions This provides a new tool to evaluate schistosomiasis survey designs across a range of transmission settings. Results highlight the importance of considering spatial structure when designing sampling strategies, illustrating that a substantial proportion of children may be undertreated even when an implementation unit is correctly classified. Control programmes need to weigh the increased accuracy of more detailed mapping strategies against the survey costs and treatment priorities

Ivermectin and albendazole coadministration: opportunities for strongyloidiasis control

7 páginas.In 2020, WHO recognised the importance of strongyloidiasis alongside soil-transmitted helminths (STH) in their 2021–30 roadmap, which aspires to target Strongyloides stercoralis with preventive chemotherapy by use of ivermectin. Combination treatment with both albendazole, the primary drug used to treat STH, and ivermectin, would improve the efficiency of mass drug administration targeting both STH and S stercoralis. In this Personal View, we discuss the challenges and opportunities towards the development of an efficient control programme for strongyloidiasis, particularly if it is to run concurrently with STH control. We argue the need to define the prevalence threshold to implement preventive chemotherapy for S stercoralis, the target populations and optimal dosing schedules, and discuss the added benefits of a fixed-dose coformulation of ivermectin and albendazole. Implementation of an efficient control programme will require improvements to current diagnostics, and validation of new diagnostics, to target and monitor S stercoralis infections, and consideration of the challenges of multispecies diagnostics for S stercoralis and STH control. Finally, the evolution of ivermectin resistance represents a credible risk to control S stercoralis; we argue that genome-wide approaches, together with improved genome resources, are needed to characterise and prevent the emergence of resistance. Overcoming these challenges will help to reduce strongyloidiasis burden and enhance the feasibility of controlling it worldwide.Our group, the Stopping Transmission of intestinal Parasites (STOP) consortium, is funded by the EDCTP2 programme supported by the European Union (RIA2017NCT-1845-STOP). The Barcelona Institute for Global Health (ISGlobal) acknowledges support from the Spanish Ministry of Science and Innovation and State Research Agency through the Centro de Excelencia Severo Ochoa 2019–2023 Program (CEX2018-000806-S) and support from the Generalitat de Catalunya through the CERCA Program. SRD is supported by a UK Research and Innovation Future Leaders Fellowship [MR/T020733/1] and the Wellcome Trust through core funding to the Wellcome Sanger Institute [108413/A/15/D]. MC-P is supported by the Junta de Castilla y León and Fondo Social Europeo. The funders of the study had no role in the manuscript preparation or the decision to publish. The views, opinions, assumptions, or any other information set out in this Personal View are solely those of the authors and should not be attributed to the funders or any person connected with the funders.Peer reviewe

Assessing the feasibility of interrupting the transmission of soil-transmitted helminths through mass drug administration: The DeWorm3 cluster randomized trial protocol

DeWorm3 collectionThe file attached is the Published/publisher’s pdf version of the article.© 2018 Ásbjörnsdóttir 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

Downhole seismic logging for high‐resolution reflection surveying in unconsolidated overburden

Downhole seismic velocity logging techniques have been developed and applied in support of high‐resolution reflection seismic surveys. For shallow high‐resolution reflection surveying within unconsolidated overburden, velocity‐depth control can sometimes be difficult to achieve; as well, unambiguous correlation of reflections with overburden stratigraphy is often problematic. Data obtained from downhole seismic logging can provide accurate velocity‐depth functions and directly correlate seismic reflections to depth. The methodologies described in this paper are designed for slimhole applications in plastic‐cased boreholes (minimum ID of 50 mm) and with source and detector arrays that yield similar frequency ranges and vertical depth resolutions as the surface reflection surveys. Compressional- (P-) wave logging uses a multichannel hydrophone array with 0.5-m detector spacings in a fluid‐filled borehole and a high‐frequency, in‐hole shotgun source at the surface. Overlapping array positions downhole results in redundant first‐arrival data (picked using interactive computer techniques), which can be processed to provide accurate interval velocities. The data also can be displayed as a record suite, showing reflections and directly correlating reflection events with depths. Example applications include identification of gas zones, lithological boundaries within unconsolidated sediments, and the overburden‐bedrock interface. Shear- (S-) wave logging uses a slimhole, well‐locked, three‐component (3-C) geophone pod and a horizontally polarized, hammer‐and‐loaded‐plate source at ground surface. The pod is moved in successive 0.5- or 1-m intervals downhole with no redundancy of overlapping data as in the P-wave method. First‐arrival data can be obtained by picking the crossover onset of polarized energy or by closely examining particle‐motion plots using all three components of motion. In unconsolidated sediments, shear‐wave velocity contrasts can be associated with changes in material density or dynamic shear modulus, which in turn can be related to consolidation. Example applications include identification of a lithological boundary for earthquake hazard applications and mapping massive ice within permafrost materials.</p