Dataset Information

Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission.

ABSTRACT: Recently, the World Health Organization recognized that efforts to interrupt schistosomiasis transmission through mass drug administration have been ineffective in some regions; one of their new recommended strategies for global schistosomiasis control emphasizes targeting the freshwater snails that transmit schistosome parasites. We sought to identify robust indicators that would enable precision targeting of these snails. At the site of the world's largest recorded schistosomiasis epidemic-the Lower Senegal River Basin in Senegal-intensive sampling revealed positive relationships between intermediate host snails (abundance, density, and prevalence) and human urogenital schistosomiasis reinfection (prevalence and intensity in schoolchildren after drug administration). However, we also found that snail distributions were so patchy in space and time that obtaining useful data required effort that exceeds what is feasible in standard monitoring and control campaigns. Instead, we identified several environmental proxies that were more effective than snail variables for predicting human infection: the area covered by suitable snail habitat (i.e., floating, nonemergent vegetation), the percent cover by suitable snail habitat, and size of the water contact area. Unlike snail surveys, which require hundreds of person-hours per site to conduct, habitat coverage and site area can be quickly estimated with drone or satellite imagery. This, in turn, makes possible large-scale, high-resolution estimation of human urogenital schistosomiasis risk to support targeting of both mass drug administration and snail control efforts.

SUBMITTER: Wood CL

PROVIDER: S-EPMC6859407 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission.

Wood Chelsea L CL Sokolow Susanne H SH Jones Isabel J IJ Chamberlin Andrew J AJ Lafferty Kevin D KD Kuris Armand M AM Jocque Merlijn M Hopkins Skylar S Adams Grant G Buck Julia C JC Lund Andrea J AJ Garcia-Vedrenne Ana E AE Fiorenza Evan E Rohr Jason R JR Allan Fiona F Webster Bonnie B Rabone Muriel M Webster Joanne P JP Bandagny Lydie L Ndione Raphaël R Senghor Simon S Schacht Anne-Marie AM Jouanard Nicolas N Riveau Gilles G De Leo Giulio A GA

Proceedings of the National Academy of Sciences of the United States of America 20191028 46

Recently, the World Health Organization recognized that efforts to interrupt schistosomiasis transmission through mass drug administration have been ineffective in some regions; one of their new recommended strategies for global schistosomiasis control emphasizes targeting the freshwater snails that transmit schistosome parasites. We sought to identify robust indicators that would enable precision targeting of these snails. At the site of the world's largest recorded schistosomiasis epidemic-the ...[more]

PMID: 31659025

Similar Datasets

Project description:BackgroundSchistosomiasis is a neglected tropical disease endemic in 54 countries. A major Schistosoma species, Schistosoma mansoni, is sustained via a life cycle that includes both human and snail hosts. Mathematical models of S. mansoni transmission, used to elucidate the complexities of the transmission cycle and estimate the impact of intervention efforts, often focus primarily on the human host. However, S. mansoni incurs physiological costs in snails that vary with the age of the snail when first infected. Snail demography and the age of snail infection could thus affect the force of infection experienced by humans, which is frequently used to predict the impact of various control strategies.MethodsTo address how these snail host and parasite interactions influence model predictions, we developed deterministic models of schistosomiasis transmission that include varying complexity in the snail population age structure. Specifically, we examined how model outputs, such as schistosome prevalence in human and snail populations, respond to the inclusion of snail age structure.ResultsOur models suggest that snail population age structure modifies the force of infection experienced by humans and the relationship between snail infection prevalence and corresponding human infection prevalence. There are significant differences in estimated snail infection, cercarial density and mean worm burden between models without snail population dynamics and those with snail populations, and between models with a homogeneous snail population and those with age stratification. The variation between finely age-stratified snail populations and those grouped into only juvenile and adult life stages is, however, minimal.ConclusionsThese results indicate that including snails and snail age structure in a schistosomiasis transmission model alters the relationship between snail and human infection prevalence. This highlights the importance of accounting for a heterogeneous intermediate host population in models of schistosomiasis transmission where the impact of proposed control measures is being considered.

Project description:IntroductionSchistosomiasis 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.Methodology and principal findingsWe 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 conventional model in terms of their predictions. A longitudinal dataset generated in Kenya field studies was used for model calibration and validation. For each sample community, we calibrated modified and conventional model systems, then used them to model outcomes for a range of MDA regimens. In most cases, the modified model predicted more vigorous post-MDA rebound, with faster relapse to baseline levels of infection. The effect was pronounced in higher risk communities. When compared to observed data, only the modified system was able to successfully predict persistent rebound of Schistosoma infection.Conclusion and significanceThe observed impact of varying location-specific snail inputs sheds light on the diverse MDA response patterns noted in operational research on schistosomiasis control, such as the recent SCORE project. Efficiency of human-to-snail transmission is likely to be much higher than predicted by standard models, which, in practice, will make local elimination by implementation of MDA alone highly unlikely, even over a multi-decade period.

Project description:BackgroundLike many trematodes of human health significance, the carcinogenic liver fluke, Opisthorchis viverrini, is spread via fecal contamination of snail habitat. Methods for assessing snail exposure to fecal waste can improve our ability to identify snail infection hotspots and potential sources of snail infections. We evaluated the feasibility of culturing fecal indicator bacteria from Bithynia snail intestinal tubes as a method for assessing snail exposure to fecal waste. Snails and water samples were collected from a site with a historically high prevalence of O. viverrini infected snails ("hotspot" site) and a site with historically no infected snails ("non-hotspot" site) on two sampling days. Snails were tested for O. viverrini and a stratified random sample of snails from each site was selected for intestinal tube removal and culture of gut contents for the fecal indicator bacteria, Escherichia coli. Water samples were tested for E. coli and nearby households were surveyed to assess sources of fecal contamination.ResultsAt the hotspot site, 26 of 2833 Bithynia siamensis goniomphalos snails were infected with O. viverrini compared to 0 of 1421 snails at the non-hotspot site. A total of 186 snails were dissected and cultured. Escherichia coli were detected in the guts of 20% of uninfected snails, 4% of O. viverrini-positive snails and 8% of snails not examined for cercarial infection at the hotspot site. Only one of 75 snails from the non-hotspot site was positive for E. coli. Accounting for sampling weights, snails at the hotspot site were more likely to have gut E. coli than snails from the non-hotspot site. The concentration of fecal indicator bacteria in surface water was higher at the hotspot vs non-hotspot site on only the first sampling day.ConclusionsFecal indicator bacteria can be detected in the intestinal tubes of Bithynia snails. The presence of fecal indicator bacteria in Bithynia snail guts may indicate risk of O. viverrini infection in snail populations. This method has the potential to aid in identifying locations and time windows of peak snail infection risk and may be applicable to other trematodes of human-health significance.

Dataset Information

Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission.

Publications

Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets