Bayesian risk mapping and model-based estimation of Schistosoma haematobium-Schistosoma mansoni co-distribution in Côte d'Ivoire

Potential associations between Schistosoma mansoni infection and physico-chemical characteristics and water-related human activities in Côte d'Ivoire: a cross-sectional study

BACKGROUND

Schistosomiasis remains a public health problem, particularly in sub-Saharan Africa. The disease is intimately connected to poverty and environmental factors. Our research was readily embedded into a multi-country schistosomiasis oversampling study. The aim of the study presented here was to determine the prevalence of Schistosoma mansoni and to investigate the role of water body characteristics and water-related human activities in disease transmission.

METHODS

In August and September 2022, a cross-sectional study was conducted in the western part of Côte d'Ivoire. Stool and urine samples were collected from 1602 and 1729 children aged 5-14 years, respectively, in 65 villages in the health districts of Biankouma, Ouaninou and Touba. Additionally, data were collected from direct observation of water-related activities at water bodies and interviews conducted with community leaders and health workers. The prevalence and risk factors for Schistosoma infection were assessed using generalised estimating equation models.

RESULTS

The prevalence ofS. mansoni and S. haematobium were 27.4% (95% confidence interval [CI] 21.5-34.3%) and 0.1% (95% CI 0.03-0.5%), respectively. Low prevalence of soil-transmitted helminths was observed with 2.4%, 0.4% and 0.2% for hookworm, Trichuris trichiura and Ascaris lumbricoides, respectively. At the health district level, we found S. mansoni prevalence of 34.4% (95% CI 25.0-45.3%), 34.3% (95% CI 24.0-46.2%) and 16.3% (95% CI 9.5-26.6%) for Biankouma, Ouaninou and Touba, respectively. Female and male participants were at a similar risk of infection (29.0% vs. 26.0%, odds ratio [OR]: 1.18, 95% CI 0.92-1.50). Children aged 9-14 years showed a higher prevalence than their younger counterparts aged 5-8 years (34.5% vs. 22.7%, OR: 1.80, 95% CI 1.42-2.27). High infection prevalence was observed in villages where children were washing clothes and dishes at open surface water sites and pursued recreational activities (e.g. swimming and playing in the water). The temperature, total dissolved solids and pH of water samples showed no significant association with S. mansoni infection at the village unit.

CONCLUSIONS

Human water-related activities such as washing clothes and playing in the water are risk factors for S. mansoni transmission. Hence, preventive chemotherapy should be combined with information, education and communication to avoid or reduce the frequency of water exposure in children as part of a comprehensive package of interventions towards elimination of schistosomiasis as a public health problem.

A systematic review and guide for using multi-response statistical models in co-infection research

The simultaneous infection of organisms with two or more co-occurring pathogens, otherwise known as co-infections, concomitant infections or multiple infections, plays a significant role in the dynamics and consequences of infectious diseases in both humans and animals. To understand co-infections, ecologists and epidemiologists rely on models capable of accommodating multiple response variables. However, given the diversity of available approaches, choosing a model that is suitable for drawing meaningful conclusions from observational data is not a straightforward task. To provide clearer guidance for statistical model use in co-infection research, we conducted a systematic review to (i) understand the breadth of study goals and host-pathogen systems being pursued with multi-response models and (ii) determine the degree of crossover of knowledge among disciplines. In total, we identified 69 peer-reviewed primary studies that jointly measured infection patterns with two or more pathogens of humans or animals in natural environments. We found stark divisions in research objectives and methods among different disciplines, suggesting that cross-disciplinary insights into co-infection patterns and processes for different human and animal contexts are currently limited. Citation network analysis also revealed limited knowledge exchange between ecology and epidemiology. These findings collectively highlight the need for greater interdisciplinary collaboration for improving disease management.

Effectiveness of Three Sampling Approaches for Optimizing Mapping and Preventive Chemotherapy against Schistosoma mansoni in the Western Part of Côte d'Ivoire

The elimination of schistosomiasis as a public health problem by 2030 is one of the main goals put forth in the World Health Organization's roadmap for neglected tropical diseases. This study aimed to compare different sampling approaches to guide mapping and preventive chemotherapy. A cross-sectional parasitological survey was conducted from August to September 2022 in the health districts of Biankouma, Ouaninou, and Touba in the western part of Côte d'Ivoire. The prevalence and intensity of Schistosoma mansoni infection were assessed in children aged 5-14 years using three sampling approaches. The first approach involved a random selection of 50% of the villages in the health districts. The second approach involved a random selection of half of the villages selected in approach 1, thus constituting 25% of the villages in the health district. The third approach consisted of randomly selecting 15 villages from villages selected by approach 2 in each health district. The overall prevalence of S. mansoni was 23.5% (95% confidence interval (CI): 19.9-27.6%), 21.6% (95% CI: 17.1-26.8%), and 18.3% (95% CI: 11.9-27.1%) with the first, second, and third approach, respectively. The respective geometric mean S. mansoni infection intensity was 117.9 eggs per gram of stool (EPG) (95% CI: 109.3-127.3 EPG), 104.6 EPG (95% CI: 93.8-116.6 EPG), and 94.6 EPG (95% CI 79.5-112.7 EPG). We conclude that, although randomly sampling up to 50% of villages in a health district provides more precise population-based prevalence and intensity measures of S. mansoni, randomly selecting only 15 villages in a district characterized by low heterogeneity provides reasonable estimates and is less costly.

Prevalence and risk factors of schistosomiasis and hookworm infection in seasonal transmission settings in northern Côte d'Ivoire: A cross-sectional study

BACKGROUND

Schistosomiasis and hookworm infection remain public health problems in large parts of sub-Saharan Africa. The epidemiology of schistosomiasis and hookworm was studied in seasonal transmission settings in the northern part of Côte d'Ivoire.

METHODOLOGY

In August 2018, a cross-sectional study was conducted. Urine and stool samples were collected from 742 individuals aged 6-96 years in 16 localities from four departments in northern Côte d'Ivoire. Urine samples were examined by a filtration method for quantification of Schistosoma haematobium eggs. Stool samples were subjected to duplicate Kato-Katz thick smears and eggs of Schistosoma mansoni and soil-transmitted helminths (STHs) were counted. Additionally, a questionnaire was administered to determine demographic characteristics and to identify risk factors of schistosomiasis and STHs. Malacologic surveys were carried out at water points that are contacted by humans and animals.

PRINCIPAL FINDINGS

The prevalence of schistosomiasis was very low. Only two cases of S. mansoni were found (0.3%, 95% confidence interval [CI]: 0.1-1.0%). The distribution of S. haematobium was focal, with cases found only in two departments; Ferkessédougou (5.4%, 95% CI: 2.5-9.9%) and Ouangolodougou (2.7%, 95% CI: 0.9-6.3%). Hookworm was the only STH species observed with a prevalence of 1.5% (95% CI: 0.8-2.8%). A higher risk of S. haematobium infection was observed in males compared to females, but the difference was not statistically significant (2.3% versus 1.3%, odds ratio [OR]: 1.5, 95% CI: 0.8-2.7). Participants aged 16-20 years showed the highest prevalence of S. haematobium. A total of 111 human- and animal-water contact points were identified at 47 water sources. Three potential intermediate host snails of schistosomes were collected; namely, Bulinus forskalii (n = 761), Bulinus truncatus (n = 205), and Biomphalaria pfeifferi (n = 1). Yet, only one specimen of Bu. truncatus was found to be shedding schistosome cercariae.

CONCLUSIONS/SIGNIFICANCE

This study confirms very low transmission of schistosomiasis and hookworm in northern Côte d'Ivoire. The establishment and rigorous implementation of integrated surveillance-response systems could lead to the elimination of schistosomiasis and hookworm in this part of Côte d'Ivoire.

Geostatistical analysis of active human cysticercosis: Results of a large-scale study in 60 villages in Burkina Faso

Cysticercosis is a neglected tropical disease caused by the larval stage of the zoonotic tapeworm (Taenia solium). While there is a clear spatial component in the occurrence of the parasite, no geostatistical analysis of active human cysticercosis has been conducted yet, nor has such an analysis been conducted for Sub-Saharan Africa, albeit relevant for guiding prevention and control strategies. The goal of this study was to conduct a geostatistical analysis of active human cysticercosis, using data from the baseline cross-sectional component of a large-scale study in 60 villages in Burkina Faso. The outcome was the prevalence of active human cysticercosis (hCC), determined using the B158/B60 Ag-ELISA, while various environmental variables linked with the transmission and spread of the disease were explored as potential explanatory variables for the spatial distribution of T. solium. A generalized linear geostatistical model (GLGM) was run, and prediction maps were generated. Analyses were conducted using data generated at two levels: individual participant data and grouped village data. The best model was selected using a backward variable selection procedure and models were compared using likelihood ratio testing. The best individual-level GLGM included precipitation (increasing values were associated with an increased odds of positive test result), distance to the nearest river (decreased odds) and night land temperature (decreased odds) as predictors for active hCC, whereas the village-level GLGM only retained precipitation and distance to the nearest river. The range of spatial correlation was estimated at 45.0 [95%CI: 34.3; 57.8] meters and 28.2 [95%CI: 14.0; 56.2] km for the individual- and village-level datasets, respectively. Individual- and village-level GLGM unravelled large areas with active hCC predicted prevalence estimates of at least 4% in the south-east, the extreme south, and north-west of the study area, while patches of prevalence estimates below 2% were seen in the north and west. More research designed to analyse the spatial characteristics of hCC is needed with sampling strategies ensuring appropriate characterisation of spatial variability, and incorporating the uncertainty linked to the measurement of outcome and environmental variables in the geostatistical analysis. Trial registration: ClinicalTrials.gov; NCT0309339.

Optimizing Implementation of Preventive Chemotherapy against Soil-Transmitted Helminthiasis and Intestinal Schistosomiasis Using High-Resolution Data: Field-Based Experiences from Côte d’Ivoire

Background: Despite efforts to control neglected tropical diseases (NTDs) using preventive chemotherapy (PC), soil-transmitted helminthiases and schistosomiasis remain widely prevalent in sub-Saharan Africa. The current PC regimen in endemic settings is defined based on health district-level prevalence. This work aims to highlight the need for high-resolution data when elimination, rather than morbidity control, is the targeted goal. Methodology: Cross-sectional parasitological surveys were conducted from July to August 2019 and from September to October 2019, respectively, across the entire Dabou and Jacqueville health districts in southern Côte d’Ivoire. From every village, 60 school-aged children (6–15 years) were randomly selected and invited to provide one fresh stool sample, whereof duplicate Kato–Katz thick smears were prepared and read by two independent technicians. Principal Findings: 4338 school-aged children from 77 villages were screened from the Dabou (n = 2174; 50.12%, 39 villages) and Jacqueville (n = 2164; 49.88%, 38 villages) health districts. The prevalence of any soil-transmitted helminth (STH) infection was 12.47% and 11.09% in the Dabou and Jacqueville health districts, respectively. Species-specific district-level prevalence remained below 10%, varying between 0.51% (hookworm in Jacqueville) and 9.06% (Trichuris trichiura in Dabou). However, when considering sub-districts or villages only, several STH infection hotspots (five sub-districts with ≥20% and four villages with more than 50% infected) were observed. Schistosoma mansoni infection was found in less than 1% of the examined children in each health district. Conclusions/Significance: We conclude that keeping health district-level prevalence as a reference for PC implementation leaves many high-risk sub-districts or villages requiring PC (≥20% prevalence) untreated. To avoid maintaining those high-risk villages as STH reservoirs by skipping control interventions and jeopardizing the successes already achieved in STH control through PC during the past two decades, precision mapping is required. Further investigation is needed to assess cost-efficient approaches to implement small-scale disease surveillance.

Population genetic structure of Schistosoma haematobium and Schistosoma haematobium × Schistosoma bovis hybrids among school-aged children in Côte d'Ivoire

While population genetics of Schistosoma haematobium have been investigated in West Africa, only scant data are available from Côte d’Ivoire. The purpose of this study was to analyze both genetic variability and genetic structure among S. haematobium populations and to quantify the frequency of S. haematobium × S. bovis hybrids in school-aged children in different parts of Côte d’Ivoire. Urine samples were subjected to a filtration method and examined microscopically for Schistosoma eggs in four sites in the western and southern parts of Côte d’Ivoire. A total of 2692 miracidia were collected individually and stored on Whatman^® FTA cards. Of these, 2561 miracidia were successfully genotyped for species and hybrid identification using rapid diagnostic multiplex mitochondrial cox1 PCR and PCR Restriction Fragment Length Polymorphism (PCR-RFLP) analysis of the nuclear ITS2 region. From 2164 miracidia, 1966 (90.9%) were successfully genotyped using at least 10 nuclear microsatellite loci to investigate genetic diversity and population structure. Significant differences were found between sites in all genetic diversity indices and genotypic differentiation was observed between the site in the West and the three sites in the East. Analysis at the infrapopulation level revealed clustering of parasite genotypes within individual children, particularly in Duekoué (West) and Sikensi (East). Of the six possible cox1-ITS2 genetic profiles obtained from miracidia, S. bovis cox1 × S. haematobium ITS2 (42.0%) was the most commonly observed in the populations. We identified only 15 miracidia (0.7%) with an S. bovis cox1 × S. bovis ITS2 genotype. Our study provides new insights into the population genetics of S. haematobium and S. haematobium × S. bovis hybrids in humans in Côte d’Ivoire and we advocate for researching hybrid schistosomes in animals such as rodents and cattle in Côte d’Ivoire.

Prevalence and effect of Plasmodium spp. and hookworm co-infection on malaria parasite density and haemoglobin level: a meta-analysis

The dual effects of co-infection of Plasmodium spp. and hookworm on malaria remain under debate. This study investigated prevalence, prevalence odds ratio (POR) of co-infection and impact of co-infection on malaria parasite density and haemoglobin levels in comparison to Plasmodium mono-infection. The protocol for this systematic review and meta-analysis is registered at PROPERO under ID: CRD42020202156. Relevant literatures were obtained from PubMed, ISI Web of Science, and Scopus on 25 December 2020. Mean difference (MD) and confidence interval (CI) of malaria parasite density and haemoglobin were compared using a random effect model. Heterogeneity was assessed using Cochrane Q and I2 statistics. Publication bias was determined by visualising funnel plot asymmetry. Of 1756 articles examined, 22,191 malaria cases across 37 studies included 6096 cases of co-infection of Plasmodium spp. and hookworm. The pooled prevalence was 20% (95% CI 15-26%, I2 99.6%, 37 studies) and was varied in terms of geographical region. Co-infection occurred by chance (OR 0.97, p 0.97, 95% CI 0.73-1.27, I2 95%, 30 studies). The mean malaria parasite density for co-infection (478 cases) was similar to Plasmodium mono-infection (920 cases) (p 0.24, MD 0.86, 95% CI - 0.58-2.29, I2 100%, 7 studies). The mean haemoglobin level for co-infection (90 cases) was similar to Plasmodium mono-infection (415 cases) (p 0.15, MD - 0.63, 95% CI - 1.49-0.23, I2 98%, 4 studies). Co-infection was common and occurred by chance but varied by geographic region. Further studies are required to investigate the mechanism of hookworm infection on malaria severity. Additionally, detection of hookworm infections among patients with malaria in endemic areas of both diseases is recommended to prevent severe malaria.

Development of New Technologies for Risk Identification of Schistosomiasis Transmission in China

Schistosomiasis is serious parasitic disease with an estimated global prevalence of active infections of more than 190 million. Accurate methods for the assessment of schistosomiasis risk are crucial for schistosomiasis prevention and control in China. Traditional approaches to the identification of epidemiological risk factors include pathogen biology, immunology, imaging, and molecular biology techniques. Identification of schistosomiasis risk has been revolutionized by the advent of computer network communication technologies, including 3S, mathematical modeling, big data, and artificial intelligence (AI). In this review, we analyze the development of traditional and new technologies for risk identification of schistosomiasis transmission in China. New technologies allow for the integration of environmental and socio-economic factors for accurate prediction of the risk population and regions. The combination of traditional and new techniques provides a foundation for the development of more effective approaches to accelerate the process of schistosomiasis elimination.

Effect of preventive chemotherapy with praziquantel on schistosomiasis among school-aged children in sub-Saharan Africa: a spatiotemporal modelling study

Background

Over the past 20 years, schistosomiasis control has been scaled up. Preventive chemotherapy with praziquantel is the main intervention. We aimed to assess the effect of preventive chemotherapy on schistosomiasis prevalence in sub-Saharan Africa, comparing 2000–10 with 2011–14 and 2015–19.

Methods

In this spatiotemporal modelling study, we analysed survey data from school-aged children (aged 5–14 years) in 44 countries across sub-Saharan Africa. The data were extracted from the Global Neglected Tropical Diseases database and augmented by 2018 and 2019 survey data obtained from disease control programmes. Bayesian geostatistical models were fitted to Schistosoma haematobium and Schistosoma mansoni survey data. The models included data on climatic predictors obtained from satellites and other open-source environmental databases and socioeconomic predictors obtained from various household surveys. Temporal changes in Schistosoma species prevalence were estimated by a categorical variable with values corresponding to the three time periods (2000–10, 2011–14, and 2015–19) during which preventive chemotherapy interventions were scaled up.

Findings

We identified 781 references with relevant geolocated schistosomiasis survey data for 2000–19. There were 19 166 unique survey locations for S haematobium and 23 861 for S mansoni, of which 77% (14 757 locations for S haematobium and 18 372 locations for S mansoni) corresponded to 2011–19. Schistosomiasis prevalence among school-aged children in sub-Saharan Africa decreased from 23·0% (95% Bayesian credible interval 22·1–24·1) in 2000–10 to 9·6% (9·1–10·2) in 2015–19, an overall reduction of 58·3%. The reduction of S haematobium was 67·9% (64·6–71·1) and that of S mansoni 53·6% (45·2–58·3) when comparing 2000–10 with 2015–19.

Interpretation

Our model-based estimates suggest that schistosomiasis prevalence in sub-Saharan Africa has decreased considerably, most likely explained by the scale-up of preventive chemotherapy. There is a need to consolidate gains in the control of schistosomiasis by means of preventive chemotherapy, coupled with other interventions to interrupt disease transmission.

Funding

European Research Council and WHO.

Prevalence and distribution of livestock schistosomiasis and fascioliasis in Côte d'Ivoire: results from a cross-sectional survey

BACKGROUND

Schistosoma and Fasciola are zoonotic parasites of public health and veterinary importance. However, while the epidemiology of schistosomiasis in humans is well studied, little is known about fascioliasis and schistosomiasis in livestock in Côte d'Ivoire. This study aimed to determine the prevalence and the distribution of livestock schistosomiasis and fascioliasis across Côte d'Ivoire. In 2018, we conducted a cross-sectional survey in abattoirs and farms in 13 departments of Côte d'Ivoire. In abattoirs, the mesenteric veins and livers of slaughtered cattle, sheep and goats were examined for adult Schistosoma and Fasciola flukes. Faeces from live cattle, goats and sheep were collected and examined for Schistosoma and Fasciola eggs using a sedimentation technique.

RESULTS

A total of 386 cattle, 174 goats and 151 sheep from abattoirs and 435 cattle, 22 goats and 176 sheep from farms were sampled. The observed prevalence of schistosomiasis was higher in slaughtered animals. Fascioliasis was more prevalent in farm animals. The prevalence of schistosomiasis in slaughtered cattle varied between 5.9% (95% confidence interval (CI): 0.7-19.7%) and 53.3% (95% CI: 37.9-68.3%) with the highest prevalence observed in Ouangolodougou in the North. Cattle from farms had a relatively low prevalence of schistosomiasis, with the highest prevalence found in Ouangolodougou (2.4%, 95% CI: 0.7-6.1%). The prevalence of fascioliasis varied considerably from one department to another, ranging from nil (95% CI: 0.0-18.5%) to 50.8% (95% CI: 43.4-58.2%), with the highest prevalence found in farm cattle in Dikodougou in the North. Sheep and goats had a lower prevalence of schistosomiasis and fascioliasis than cattle. In slaughtered animals, cattle aged 4 years and older were at highest risk for schistosomiasis (odds ratio (OR): 2.4; 95% CI: 1.0-5.6) and fascioliasis (OR: 2.1; 95% CI: 1.1-3.9). In farm animals, male cattle had higher odds of being infected with Schistosoma (OR: 4.3; 95% CI: 0.7-26.9) than females.

CONCLUSIONS

Our study confirms that schistosomiasis and fascioliasis are endemic in livestock across Côte d'Ivoire. A strategic control programme should be considered, especially for cattle, including providing drinking water in troughs to reduce faecal contamination of water sources by cattle.

Schistosoma haematobium infection and environmental factors in Southwestern Tanzania: A cross-sectional, population-based study

Schistosomiasis is a leading cause of morbidity in Africa. Understanding the disease ecology and environmental factors that influence its distribution is important to guide control efforts. Geographic information systems have increasingly been used in the field of schistosomiasis environmental epidemiology. This study reports prevalences of Schistosoma haematobium infection and uses remotely sensed and questionnaire data from over 17000 participants to identify environmental and socio-demographic factors that are associated with this parasitic infection. Data regarding socio-demographic status and S. haematobium infection were obtained between May 2006 and May 2007 from 17280 participants (53% females, median age = 17 years) in the Mbeya Region, Tanzania. Combined with remotely sensed environmental data (vegetation cover, altitude, rainfall etc.) this data was analyzed to identify environmental and socio-demographic factors associated with S. haematobium infection, using mixed effects logistic regression and geostatistical modelling. The overall prevalence of S. haematobium infection was 5.3% (95% confidence interval (CI): 5.0-5.6%). Multivariable analysis revealed increased odds of infection for school-aged children (5-15 years, odds ratio (OR) = 7.8, CI: 5.9-10.4) and the age groups 15-25 and 25-35 years (15-25 years: OR = 5.8, CI: 4.3-8.0, 25-35 years: OR = 1.6, CI: 1.1-2.4) compared to persons above 35 years of age, for increasing distance to water courses (OR = 1.4, CI: 1.2-1.6 per km) and for proximity to Lake Nyasa (<1 km, OR = 4.5, CI: 1.8-11.4; 1-2 km, OR = 3.5, CI: 1.7-7.5; 2-4 km; OR = 3.3, CI: 1.7-6.6), when compared to distances >4 km. Odds of infection decreased with higher altitude (OR = 0.7, CI: 0.6-0.8 per 100 m increase) and with increasing enhanced vegetation index EVI (OR = 0.2, CI: 0.1-0.4 per 0.1 units). When additionally adjusting for spatial correlation population density became a significant predictor of schistosomiasis infection (OR = 1.3, CI: 1.1-1.5 per 1000 persons/km2) and altitude turned non-significant. We found highly focal geographical patterns of S. haematobium infection in Mbeya Region in Southwestern Tanzania. Despite low overall prevalence our spatially heterogeneous results show that some of the study sites suffer from a considerable burden of S. haematobium infection, which is related to various socio-demographic and environmental factors. Our results could help to design more effective control strategies in the future, especially targeting school-aged children living in low altitude sites and/or crowded areas as the persons at highest need for preventive chemotherapy.

High prevalence of Schistosoma haematobium × Schistosoma bovis hybrids in schoolchildren in Côte d'Ivoire

Schistosomiasis is a neglected tropical disease, though it is highly prevalent in many parts of sub-Saharan Africa. While Schistosoma haematobium-bovis hybrids have been reported in West Africa, no data about Schistosoma hybrids in humans are available from Côte d'Ivoire. This study aimed to identify and quantify S. haematobium-bovis hybrids among schoolchildren in four localities of Côte d'Ivoire. Urine samples were collected and examined by filtration to detect Schistosoma eggs. Eggs were hatched and 503 miracidia were individually collected and stored on Whatman® FTA cards for molecular analysis. Individual miracidia were molecularly characterized by analysis of mitochondrial cox1 and nuclear internal transcribed spacer 2 (ITS 2) DNA regions. A mitochondrial cox1-based diagnostic polymerase chain reaction was performed on 459 miracidia, with 239 (52.1%) exhibiting the typical band for S. haematobium and 220 (47.9%) the S. bovis band. The cox1 and ITS 2 amplicons were Sanger sequenced from 40 randomly selected miracidia to confirm species and hybrids status. Among the 33 cox1 sequences analysed, we identified 15 S. haematobium sequences (45.5%) belonging to seven haplotypes and 18 S. bovis sequences (54.5%) belonging to 12 haplotypes. Of 40 ITS 2 sequences analysed, 31 (77.5%) were assigned to pure S. haematobium, four (10.0%) to pure S. bovis and five (12.5%) to S. haematobium-bovis hybrids. Our findings suggest that S. haematobium-bovis hybrids are common in Côte d'Ivoire. Hence, intense prospection of domestic and wild animals is warranted to determine whether zoonotic transmission occurs.

Prevalence and Risk Factors for Schistosomiasis among Schoolchildren in two Settings of Côte d'Ivoire

Schistosomiasis is a parasitic disease affecting more than 250 million people, primarily in sub-Saharan Africa. In Côte d’Ivoire both Schistosoma haematobium (causing urogenital schistosomiasis) and Schistosoma mansoni (causing intestinal schistosomiasis) co-exist. This study aimed to determine the prevalence of S. haematobium and S. mansoni and to identify risk factors among schoolchildren in the western and southern parts of Côte d’Ivoire. From January to April 2018, a cross-sectional study was carried out including 1187 schoolchildren aged 5–14 years. Urine samples were examined by a filtration method to identify and count S. haematobium eggs, while stool samples were subjected to duplicate Kato-Katz thick smears to quantify eggs of S.mansoni and soil-transmitted helminths. Data on sociodemographic, socioeconomic, and environmental factors were obtained using a pretested questionnaire. Multivariate logistic regression was employed to test for associations between variables. We found a prevalence of S. haematobium of 14.0% (166 of 1187 schoolchildren infected) and a prevalence of S. mansoni of 6.1% (66 of 1089 schoolchildren infected). In the southern part of Côte d’Ivoire, the prevalence of S. haematobium was 16.1% with a particularly high prevalence observed in Sikensi (35.6%), while S. mansoni was most prevalent in Agboville (11.2%). Swimming in open freshwater bodies was the main risk factor for S. haematobium infection (adjusted odds ratio (AOR) = 127.0, 95% confidence interval (CI): 25.0–634.0, p < 0.001). Fishing and washing clothes in open freshwater bodies were positively associated with S. haematobium and S. mansoni infection, respectively. Preventive chemotherapy using praziquantel should be combined with setting-specific information, education, and communication strategies in order to change children’s behavior, thus avoiding contact with unprotected open freshwater.

Modeling Schistosoma japonicum Infection under Pure Specification Bias: Impact of Environmental Drivers of Infection

Uncertainties in spatial modeling studies of schistosomiasis (SCH) are relevant for the reliable identification of at-risk populations. Ecological fallacy occurs when ecological or group-level analyses, such as spatial aggregations at a specific administrative level, are carried out for an individual-level inference. This could lead to the unreliable identification of at-risk populations, and consequently to fallacies in the drugs’ allocation strategies and their cost-effectiveness. A specific form of ecological fallacy is pure specification bias. The present research aims to quantify its effect on the parameter estimates of various environmental covariates used as drivers for SCH infection. This is done by (i) using a spatial convolution model that removes pure specification bias, (ii) estimating group and individual-level covariate regression parameters, and (iii) quantifying the difference between the parameter estimates and the predicted disease outcomes from the convolution and ecological models. We modeled the prevalence of Schistosoma japonicum using group-level health outcome data, and city-level environmental data as a proxy for individual-level exposure. We included environmental data such as water and vegetation indexes, distance to water bodies, day and night land surface temperature, and elevation. We estimated and compared the convolution and ecological model parameter estimates using Bayesian statistics. Covariate parameter estimates from the convolution and ecological models differed between 0.03 for the nearest distance to water bodies (NDWB), and 0.28 for the normalized difference water index (NDWI). The convolution model presented lower uncertainties in most of the parameter estimates, except for NDWB. High differences in uncertainty were found in night land surface temperature (0.23) and elevation (0.13). No significant differences were found between the predicted values and their uncertainties from both models. The proposed convolution model is able to correct for a pure specification bias by presenting less uncertain parameter estimates. It shows a good predictive performance for the mean prevalence values and for a positive number of infected people. Further research is needed to better understand the spatial extent and support of analysis to reliably explore the role of environmental variables.

Association of riverine prawns and intermediate host snails and correlation with human schistosomiasis in two river systems in south-eastern Côte d'Ivoire

The current emphasis of schistosomiasis control is placed on preventive chemotherapy using praziquantel. However, reinfection may occur rapidly in the absence of complementary interventions. Recent studies from Senegal suggest that predatory prawns might feed on intermediate host snails and thus impact on schistosomiasis transmission. We designed a study with four repeated cross-sectional surveys pertaining to prawns and snails, coupled with a single cross-sectional parasitological survey among humans. We assessed for potential associations between the presence/density of prawns and snails and correlation with Schistosoma infection in a composite sample of school-aged children and adults. The study was carried out between October 2015 and December 2016 in 24 villages located near the Agnéby and Mé coastal river systems in south-eastern Côte d'Ivoire. At each site, snails and prawns were collected, and in each village, 150 individuals were subjected to stool and urine examination for the diagnosis of Schistosoma mansoni and S. haematobium. We found peaks of relative abundance of intermediate host snails in the villages of the Agnéby River system, while predatory prawns were predominantly recorded in the Mé River system. A negative association was observed between intermediate host snail densities and riverine prawns; however, no pattern was found between this trend in the predator-prey relationship and the prevalence of human schistosomiasis.

Community knowledge, attitudes and practices related to schistosomiasis and associated healthcare-seeking behaviours in northern Côte d'Ivoire and southern Mauritania

Background

Among parasitic infections, schistosomiasis ranks second after malaria in terms of worldwide morbidity. Despite efforts to contain transmission, more than 230 million people are infected, of which 85% live in Sub-Saharan Africa. While the epidemiologic characteristics of schistosomiasis have been extensively studied across endemic settings, social factors have been paid less attention. The current study assesses community knowledge of schistosomiasis causes, transmission, signs, symptoms and prevention, as well as healthcare-seeking behaviours in two West African settings, with the aim of strengthening schistosomiasis control interventions.

Methods

From August 2014 to June 2015, we conducted two cross-sectional surveys in Korhogo, Côte d’Ivoire and Kaédi, Mauritania. We applied a questionnaire to collect quantitative data at the household level in Korhogo (n = 1456) and Kaédi (n = 1453). Focus group discussions (Korhogo: n = 32, Kaédi: n = 32) and participatory photography (photovoice) (Korhogo: n = 16, Kaédi: n = 16) were conducted within the communities to gather qualitative data. In addition, semi-structured interviews were used to discuss with key informants from control programmes, non-governmental organizations and health districts (Korhogo: n = 8, Kaédi: n = 7).

Results

The study demonstrated that schistosomiasis is not well known by the communities; 64.1% claimed to know the causes of the disease, but the reality is different. This knowledge is more from cultural than biomedical source. It was observed that social construction of the disease is different from the biomedical definition. In Korhogo, schistosomiasis was often associated with several other diseases, notably stomach ulcer and gonorrhoea. The populations believe that schistosomiasis is caused by exposure to goat or dog urine in the environment. In Kaédi, schistosomiasis is considered as a disease transmitted by environmenal elements such as sunshine and dirty water. In both settings, the care-seeking pathways were found to be strongly influenced by local customs and self-medication acquired from the informal sector.

Conclusions

This study revealed that knowledge about the aetiology, transmission, symptoms, prevention and treatment of schistosomiasis among the populations in Korhogo and Kaédi is based on their local culture. Deep-rooted habits could therefore pose a significant obstacle to the elimination of schistosomiasis.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0453-0) contains supplementary material, which is available to authorized users.

Schistosoma haematobium Egg Excretion does not Increase after Exercise: Implications for Diagnostic Testing

Children are frequently invited to exercise before micturition, as it is believed that this activity will result in higher Schistosoma haematobium egg excretion, and hence, increases sensitivity of microscopic diagnoses. However, the evidence of this recommendation is scant. In the study presented here, 257 children, aged 2-15 years from south Côte d'Ivoire, provided urine samples for microscopy on consecutive days; one sample without prior exercise and one sample after exercise. Comparing the same individuals without and with prior exercise, sample positivity for S. haematobium (25.7% versus 23.0%, P = 0.31) and mean egg counts (10.2 eggs/10 mL versus 8.5 eggs/10 mL, P = 0.45) did not differ. Exercise before urine collection does not appear to increase S. haematobium egg excretion.

Spatio-temporal analysis of small-area intestinal parasites infections in Ghana

Intestinal parasites infection is a major public health burden in low and middle-income countries. In Ghana, it is amongst the top five morbidities. In order to optimize scarce resources, reliable information on its geographical distribution is needed to guide periodic mass drug administration to populations of high risk. We analyzed district level morbidities of intestinal parasites between 2010 and 2014 using exploratory spatial analysis and geostatistics. We found a significantly positive Moran’s Index of spatial autocorrelation for each year, suggesting that adjoining districts have similar risk levels. Using local Moran’s Index, we found high-high clusters extending towards the Guinea and Sudan Savannah ecological zones, whereas low-low clusters extended within the semi-deciduous forest and transitional ecological zones. Variograms indicated that local and regional scale risk factors modulate the variation of intestinal parasites. Poisson kriging maps showed smoothed spatially varied distribution of intestinal parasites risk. These emphasize the need for a follow-up investigation into the exact determining factors modulating the observed patterns. The findings also underscored the potential of exploratory spatial analysis and geostatistics as tools for visualizing the spatial distribution of small area intestinal worms infections.

Mapping Soil Transmitted Helminths and Schistosomiasis under Uncertainty: A Systematic Review and Critical Appraisal of Evidence

BACKGROUND

Spatial modelling of STH and schistosomiasis epidemiology is now commonplace. Spatial epidemiological studies help inform decisions regarding the number of people at risk as well as the geographic areas that need to be targeted with mass drug administration; however, limited attention has been given to propagated uncertainties, their interpretation, and consequences for the mapped values. Using currently published literature on the spatial epidemiology of helminth infections we identified: (1) the main uncertainty sources, their definition and quantification and (2) how uncertainty is informative for STH programme managers and scientists working in this domain.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a systematic literature search using the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) protocol. We searched Web of Knowledge and PubMed using a combination of uncertainty, geographic and disease terms. A total of 73 papers fulfilled the inclusion criteria for the systematic review. Only 9% of the studies did not address any element of uncertainty, while 91% of studies quantified uncertainty in the predicted morbidity indicators and 23% of studies mapped it. In addition, 57% of the studies quantified uncertainty in the regression coefficients but only 7% incorporated it in the regression response variable (morbidity indicator). Fifty percent of the studies discussed uncertainty in the covariates but did not quantify it. Uncertainty was mostly defined as precision, and quantified using credible intervals by means of Bayesian approaches.

CONCLUSION/SIGNIFICANCE

None of the studies considered adequately all sources of uncertainties. We highlighted the need for uncertainty in the morbidity indicator and predictor variable to be incorporated into the modelling framework. Study design and spatial support require further attention and uncertainty associated with Earth observation data should be quantified. Finally, more attention should be given to mapping and interpreting uncertainty, since they are relevant to inform decisions regarding the number of people at risk as well as the geographic areas that need to be targeted with mass drug administration.

Evaluation of a Urine Pooling Strategy for the Rapid and Cost-Efficient Prevalence Classification of Schistosomiasis

BACKGROUND

A key epidemiologic feature of schistosomiasis is its focal distribution, which has important implications for the spatial targeting of preventive chemotherapy programs. We evaluated the diagnostic accuracy of a urine pooling strategy using a point-of-care circulating cathodic antigen (POC-CCA) cassette test for detection of Schistosoma mansoni, and employed simulation modeling to test the classification accuracy and efficiency of this strategy in determining where preventive chemotherapy is needed in low-endemicity settings.

METHODOLOGY

We performed a cross-sectional study involving 114 children aged 6-15 years in six neighborhoods in Azaguié Ahoua, south Côte d'Ivoire to characterize the sensitivity and specificity of the POC-CCA cassette test with urine samples that were tested individually and in pools of 4, 8, and 12. We used a Bayesian latent class model to estimate test characteristics for individual POC-CCA and quadruplicate Kato-Katz thick smears on stool samples. We then developed a microsimulation model and used lot quality assurance sampling to test the performance, number of tests, and total cost per school for each pooled testing strategy to predict the binary need for school-based preventive chemotherapy using a 10% prevalence threshold for treatment.

PRINCIPAL FINDINGS

The sensitivity of the urine pooling strategy for S. mansoni diagnosis using pool sizes of 4, 8, and 12 was 85.9%, 79.5%, and 65.4%, respectively, when POC-CCA trace results were considered positive, and 61.5%, 47.4%, and 30.8% when POC-CCA trace results were considered negative. The modeled specificity ranged from 94.0-97.7% for the urine pooling strategies (when POC-CCA trace results were considered negative). The urine pooling strategy, regardless of the pool size, gave comparable and often superior classification performance to stool microscopy for the same number of tests. The urine pooling strategy with a pool size of 4 reduced the number of tests and total cost compared to classical stool microscopy.

CONCLUSIONS/SIGNIFICANCE

This study introduces a method for rapid and efficient S. mansoni prevalence estimation through examining pooled urine samples with POC-CCA as an alternative to widely used stool microscopy.

Sustaining the Control of Schistosoma mansoni in Western Côte d'Ivoire: Baseline Findings Before the Implementation of a Randomized Trial

We report baseline findings before the implementation of a 4-year intervention trial designed to assess the impact of three different school-based treatment schedules with praziquantel to sustain the control of intestinal schistosomiasis. The baseline survey was conducted in 75 schools of western Côte d'Ivoire previously identified with moderate Schistosoma mansoni endemicity (prevalence: 10-24% in children aged 13-14 years). Three stool samples collected over consecutive days were subjected to duplicate Kato-Katz thick smears each. A questionnaire was administered to collect village-specific information that is relevant for schistosomiasis transmission. Overall, 4,953 first graders (aged 5-8 years) and 7,011 school children (aged 9-12 years) had complete parasitologic data. The overall prevalence of S. mansoni was 5.4% among first graders and 22.1% in 9- to 12-year-old children. Open defecation was practiced in all villages. The current baseline findings will be important to better understand the dynamics of S. mansoni prevalence and intensity over the course of this trial that might be governed by village characteristics and specific treatment interventions.

Access to, and use of, water by populations living in a schistosomiasis and fascioliasis co-endemic area of northern Côte d'Ivoire

Water is an essential element of life, but it can also be a source of disease. Apart from direct consumption of unsafe water, direct contact and indirect consumption puts people at risk of many different types of pathogens. Employing a mixed methods approach, consisting of questionnaires and direct observations, we assessed access to, and use of, different water sources by the participants of the district des Savanes in northern Côte d'Ivoire. The use of water sources was put in relation to the potential risk of acquiring schistosomiasis and fascioliasis. Overall, 489 people aged 8 to 82 years participated. While all participants had access to safe water, 63% were in direct contact with unimproved water and 31% directly consumed unsafe water. More than a third of the people who otherwise reported using only improved water for all activities came in contact with unimproved water through crossing open water when going to their workplace, school or other destinations. Self-reported blood in urine - a marker for Schistosoma haematobium with reasonable sensitivity and specificity - was reported by 6% (n=30), self-reported blood in stool - an unspecific marker for Schistosoma mansoni - was reported by 7% (n=35), while blood co-occurring in both urine and stool was reported by another 10% (n=48) of participants. Accessing unimproved water for any activity (including crossing) was associated with higher odds of reporting blood in urine and/or blood in stool (odds ratio: 1.90; 95% confidence interval: 1.07-3.36). Our results have important rami-fications for intervention programmes targeting neglected tropical diseases, and emphasize the need for a wider supply of safe water to rural populations, since the water supply at the workplace needs to be considered as well next to the water supply at home. Crossing of open water sources is an important risk factor for sustained transmission of schistosomiasis.

Spatial distribution of schistosomiasis and treatment needs in sub-Saharan Africa: a systematic review and geostatistical analysis

BACKGROUND

Schistosomiasis affects more than 200 million individuals, mostly in sub-Saharan Africa, but empirical estimates of the disease burden in this region are unavailable. We used geostatistical modelling to produce high-resolution risk estimates of infection with Schistosoma spp and of the number of doses of praziquantel treatment needed to prevent morbidity at different administrative levels in 44 countries.

METHODS

We did a systematic review to identify surveys including schistosomiasis prevalence data in sub-Saharan Africa via PubMed, ISI Web of Science, and African Journals Online, from inception to May 2, 2014, with no restriction of language, survey date, or study design. We used Bayesian geostatistical meta-analysis and rigorous variable selection to predict infection risk over a grid of 1 155 818 pixels at 5 × 5 km, on the basis of environmental and socioeconomic predictors and to calculate the number of doses of praziquantel needed for prevention of morbidity.

FINDINGS

The literature search identified Schistosoma haematobium and Schistosoma mansoni surveys done in, respectively, 9318 and 9140 unique locations. Infection risk decreased from 2000 onwards, yet estimates suggest that 163 million (95% Bayesian credible interval [CrI] 155 million to 172 million; 18·5%, 17·6-19·5) of the sub-Saharan African population was infected in 2012. Mozambique had the highest prevalence of schistosomiasis in school-aged children (52·8%, 95% CrI 48·7-57·8). Low-risk countries (prevalence among school-aged children lower than 10%) included Burundi, Equatorial Guinea, Eritrea, and Rwanda. The numbers of doses of praziquantel needed per year were estimated to be 123 million (95% CrI 121 million to 125 million) for school-aged children and 247 million (239 million to 256 million) for the entire population.

INTERPRETATION

Our results will inform policy makers about the number of treatments needed at different levels and will guide the spatial targeting of schistosomiasis control interventions.

FUNDING

European Research Council, China Scholarship Council, UBS Optimus Foundation, and Swiss National Science Foundation.