Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission (original) (raw)
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Schistosomiasis Control in Ethiopia: The Role of Snail Mapping in Endemic Communities
Tropical Medicine and Infectious Disease
Introduction: Schistosomiasis, a neglected tropical disease (NTD), remains a public health problem in Ethiopia. Freshwater snails, acting as intermediate hosts, release cercariae, the infectious parasite, into the water, which penetrate human skin that encounters infested waters. The objective of this study was to map snail abundance along rivers and study its association with schistosomiasis infection in communities using these rivers. Materials and Methods: A cross-sectional study was carried out at 20 river sites in Mizan Aman city administration, Bench Sheko zone, South West Ethiopia Peoples (SWEP) region, Ethiopia, to study the distribution of host snails and transmission sites for intestinal schistosomiasis. This study used a quantitative database consisting of data on the prevalence of infected snails, the characteristics of rivers and riverbanks, and the prevalence of schistosomiasis in the community, based on stool samples collected from community members near the sampling ...
BackgroundThere is growing recognition that mass drug administration must be complemented with environmental interventions to interrupt schistosomiasis transmission. Accurate mapping of snails and schistosome parasite distribution is critical to identify foci of human exposure and prioritize sites for interventions.MethodologyWe conducted longitudinal environmental surveys of snails and schistosomes in 467 waterbodies across 86 villages in northwestern Tanzania to describe spatial and temporal variation in snail and schistosome parasites presence and identify relevant underlying predictors. We conducted time constrained net sampling ofBulinussnails from vegetation, sediments, and floating objects and then examined all collected snails for patent infections.Principal findingsA total of 43,272Bulinussnails were collected across the three visits to each waterbody spanning November 2020 – August 2021, and we conducted statistical analyses on the latter two visits with more in-depth surv...
PLoS neglected tropical diseases, 2018
Schistosomiasis is a chronic parasitic trematode disease that affects over 240 million people worldwide. The Schistosoma lifecycle is complex, involving transmission via specific intermediate-host freshwater snails. Predictive mathematical models of Schistosoma transmission have often chosen to simplify or ignore the details of environmental human-snail interaction in their analyses. Schistosome transmission models now aim to provide better precision for policy planning of elimination of transmission. This heightens the importance of including the environmental complexity of vector-pathogen interaction in order to make more accurate projections. We propose a nonlinear snail force of infection (FOI) that takes into account an intermediate larval stage (miracidium) and snail biology. We focused, in particular, on the effects of snail force of infection (FOI) on the impact of mass drug administration (MDA) in human communities. The proposed (modified) model was compared to a convention...
PLoS neglected tropical diseases, 2016
Despite control efforts, human schistosomiasis remains prevalent throughout Africa, Asia, and South America. The global schistosomiasis burden has changed little since the new anthelmintic drug, praziquantel, promised widespread control. We evaluated large-scale schistosomiasis control attempts over the past century and across the globe by identifying factors that predict control program success: snail control (e.g., molluscicides or biological control), mass drug administrations (MDA) with praziquantel, or a combined strategy using both. For data, we compiled historical information on control tactics and their quantitative outcomes for all 83 countries and territories in which: (i) schistosomiasis was allegedly endemic during the 20th century, and (ii) schistosomiasis remains endemic, or (iii) schistosomiasis has been "eliminated," or is "no longer endemic," or transmission has been interrupted. Widespread snail control reduced prevalence by 92 ± 5% (N = 19) vs....
PLOS Neglected Tropical Diseases, 2021
Schistosome parasites infect more than 200 million people annually, mostly in sub-Saharan Africa, where people may be co-infected with more than one species of the parasite. Infection risk for any single species is determined, in part, by the distribution of its obligate intermediate host snail. As the World Health Organization reprioritizes snail control to reduce the global burden of schistosomiasis, there is renewed importance in knowing when and where to target those efforts, which could vary by schistosome species. This study estimates factors associated with schistosomiasis risk in 16 villages located in the Senegal River Basin, a region hyperendemic for Schistosoma haematobium and S. mansoni. We first analyzed the spatial distributions of the two schistosomes’ intermediate host snails (Bulinus spp. and Biomphalaria pfeifferi, respectively) at village water access sites. Then, we separately evaluated the relationships between human S. haematobium and S. mansoni infections and ...
Spatial patterns of urinary schistosomiasis infection in a highly endemic area of coastal Kenya
The American journal of tropical medicine and hygiene, 2004
Urinary schistosomiasis remains a major contributor to the disease burden along the southern coast of Kenya. Selective identification of transmission hot spots offers the potential for more effective, highly-focal snail control and human chemotherapy to reduce Schistosoma haematobium transmission. In the present study, a geographic information system was used to integrate demographic, parasitologic, and household location data for an endemic village and neighboring households with the biotic, abiotic, and location data for snail collection/water contact sites. A global spatial statistic was used to detect area-wide trends of clustering for human infection at the household level. Local spatial statistics were then applied to detect specific household clusters of infection, and, as a focal spatial statistic, to evaluate clustering of infection around a putative transmission site. High infection intensities were clustered significantly around a water contact site with high numbers of s...
Schistosomiasis remains a major public health problem with estimated 240 million cases worldwide whereby more than 90% of these occur in Sub-Saharan Africa. Tanzania is ranked second after Nigeria in terms of disease burden with prevalence of infection as higher as 100% in some communities. We conducted a cross-sectional malacological survey to examine for abundance, identity and disease transmission potential of snails in fishing communities of Mwanza region, Tanzania. Snails were collected from selected sites with high human water contact using standard methods. The most abundant snails species were Biomphalaria sudanica which accounted for 81.25% (n=1470) of snails collected.. Bulinus nasutus was the second abundant snail accounting for 13.87% (n=251) while Bulinus globosus was the least abundant snail accounting for 4.86% (n=88). Only 0.57% (n=11) of collected Biomphalaria snails were shedding S. mansoni cercariae while none of the Bulinus snail species were shedding cercariae. Vegetation cover was significantly associated with snail abundance (P<0.001). A positive correlation between water temperature and snail abundance was observed. No correlation was found between pH and snail abundance. The low numbers of snails shedding schistosome cercariae could be as a result of many factors including timing of the study in relation to transmission season.