Geostatistical Model-Based Estimates of Schistosomiasis Prevalence among Individuals Aged ≤20 Years in West Africa

Abstract

BackgroundSchistosomiasis is a water-based disease that is believed to affect over 200 million people with an estimated 97% of the infections concentrated in Africa. However, these statistics are largely based on population re-adjusted data originally published by Utroska and colleagues more than 20 years ago. Hence, these estimates are outdated due to large-scale preventive chemotherapy programs, improved sanitation, water resources development and management, among other reasons. For planning, coordination, and evaluation of control activities, it is essential to possess reliable schistosomiasis prevalence maps.MethodologyWe analyzed survey data compiled on a newly established open-access global neglected tropical diseases database (i) to create smooth empirical prevalence maps for Schistosoma mansoni and S. haematobium for individuals aged ≤20 years in West Africa, including Cameroon, and (ii) to derive country-specific prevalence estimates. We used Bayesian geostatistical models based on environmental predictors to take into account potential clustering due to common spatially structured exposures. Prediction at unobserved locations was facilitated by joint kriging.Principal FindingsOur models revealed that 50.8 million individuals aged ≤20 years in West Africa are infected with either S. mansoni, or S. haematobium, or both species concurrently. The country prevalence estimates ranged between 0.5% (The Gambia) and 37.1% (Liberia) for S. mansoni, and between 17.6% (The Gambia) and 51.6% (Sierra Leone) for S. haematobium. We observed that the combined prevalence for both schistosome species is two-fold lower in Gambia than previously reported, while we found an almost two-fold higher estimate for Liberia (58.3%) than reported before (30.0%). Our predictions are likely to overestimate overall country prevalence, since modeling was based on children and adolescents up to the age of 20 years who are at highest risk of infection.Conclusion/SignificanceWe present the first empirical estimates for S. mansoni and S. haematobium prevalence at high spatial resolution throughout West Africa. Our prediction maps allow prioritizing of interventions in a spatially explicit manner, and will be useful for monitoring and evaluation of schistosomiasis control programs.

Geographical analysis of the role of water supply and sanitation in the risk of helminth infections of children in West Africa

“…For the West African countries included in our analysis, the results highlight priority areas for targeting integrated helminth control that includes WASH interventions. These results holds particularly true in the Niger River basin where we found considerable geographical heterogeneity in the distribution of schistosomiasis and hookworm burden compared with previous work in the region (24,38,39). The results of this study show that the areas of maximal S. hematobium and hookworm predicted risk (>50%) straddling the southern borders of Burkina Faso and Mali were much smaller than predicted in our previous work (24,38).…”

Local spatial clustering of stunting and wasting among children under the age of 5 years: implications for intervention strategies

“…With an ultimate aim of optimizing interventions, spatial approaches have been used extensively in dealing with public health problems such as infectious diseases, malaria, intestinal nematodes and diarrhoea (9)(10)(11)(12)(13) . For example, spatial approaches through an identification of the local clustering of malaria cases have been used to identify 'hot spots' of malaria cases in an area (14) and to guide malaria control and response efforts (15) .…”

“…The clusters identified in using this analytical approach are areas having a higher risk than the expected risk for the underlying at-risk population (8) . This approach assists in appropriate geographical targeting and determining the scale of planned interventions through identifying and delineating the physical locations, sizes and intensity of the clusters (high-risk areas).With an ultimate aim of optimizing interventions, spatial approaches have been used extensively in dealing with public health problems such as infectious diseases, malaria, intestinal nematodes and diarrhoea (9)(10)(11)(12)(13) . For example, spatial approaches through an identification of the local clustering of malaria cases have been used to identify 'hot spots' of malaria cases in an area (14) and to guide malaria control and response efforts (15) .…”

Schistosomiasis transmission; socio-demographic, knowledge and practices as transmission risk factors in pregnant women

“…Nigeria is one of the most endemic regions of Africa with an overall estimate of about 26 million people (Schur et al 2011). The factors responsible for the spread of schistosomiasis in the tropics are not limited to the interplay between the human host, snail host and the parasite but also of complex demographic, environmental, biological, socioeconomic and cultural processes (WHO/ TDR 2008).…”