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Uncertainty propagation through the process chain of mapping and modelling helminth infections. Pink box: uncertainty from information data sources. Orange box: uncertainty from the predictive model. Yellow box: uncertainty in the predictions. doi:10.1371/journal.pntd.0005208.g002
Source publication
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 i...
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Citations
... The resulting study estimated ward-level prevalence throughout the Lake Zone districts to facilitate targeted decision-making for MDA in spite of existing data scarcity issues. While other spatial and geostatistical models for estimating schistosomiasis prevalence have been developed [14,16,[18][19][20][21][22][23], few NTD programs in high burden countries have integrated such tools into their decision making processes for MDA planning. ...
Introduction
To address problems of over- and under-treatment with preventive chemotherapy resulting in ongoing transmission of schistosomiasis, the World Health Organization (WHO) recommends targeted mass drug administration (MDA) interventions at a sub-district level. In Tanzania, the lack of sub-district (ward) prevalence data has inhibited a transition to targeted treatment. Model-based prevalence estimation combined with routine surveillance data can be used to overcome this gap. We created a geostatistical model to estimate parasitological prevalence in the wards of the Lake Zone regions of Tanzania to investigate opportunities for enabling targeted MDA for schistosomiasis. With no precedent on how outputs from a geostatistical model could be used to inform decision-making in Tanzania, this qualitative study explores perceptions on what may challenge and motivate program staff in Tanzania’s national schistosomiasis control program to integrate the models into routine planning to guide disease control interventions.
Methods
Seven semi-structured, key informant interviews were conducted in 2022 examining perceived programmatic challenges and motivations of integrating the geostatistical model into current programming through various thematic areas: information systems, financing, services and operational capacity, policy and planning, and coordination. Key informants included decision-making staff in the Ministry of Health’s neglected tropical diseases (NTD) control program, WHO NTD staff, schistosomiasis MDA implementing partners, academic experts studying the control of schistosomiasis, and central-level NTD coordinators.
Results
Informants unanimously acknowledged that the geostatistical model could be useful in guiding targeted interventions, and found several factors that may motivate programmatic uptake including providing a financially feasible method to comprehensive prevalence estimates, facilitation of essential implementation tasks like site selection for MDA and screening, as well as annual calculation of treatments required for requesting medicine. Key challenges to integration were seen in limitation of existing modeling expertise, sensitization, and most importantly in the lack of WHO recommendations surrounding model use, as national disease control strategies and policies are built around WHO guidelines.
Conclusions
Geostatistical models like the one presented can feasibly be integrated in decision-making for targeted interventions based on domestic capacity, financial availability and readiness. However, the lack of WHO guidance on the use of these tools calls for action to translate the potential of such models into recommendations that encourage routine integration from national programs. Overcoming this key inhibiting factor will be a crucial first step toward the integration of such models.
... Although schistosomiasis is treatable and preventable, but it can lead to debilitating clinical complications such as bladder ulceration and deformities, infertility, kidney blockage as well as liver and spleen enlargement when left untreated [9]. People working in contact with natural water bodies especially women and children continue to be at great risk of schistosomiasis infection across Sub-Saharan Africa [10]. Houweling et al. (2016) [8] reported that there would be ultimate reduction in the population prevalence of schistosomiasis when maximum prevention is achieved among these susceptible groups as this can reduce the transmission rate among the general population. ...
Schistosomiasis is the most common parasitic disease in the world caused by digenetic blood trematode worms of the family Schistosomatidae. It is one of the most prevalent neglected tropical diseases and the second most important human parasitic disease in the world, after malaria. Over 700 million people worldwide are at risk of infection, most of whom live in sub-Saharan Africa. While, children are especially vulnerable to the disease, Ogun State was rated as the most endemic state for schistosomiasis infection in Nigeria. Therefore, the epidemiology of Urinary Schistosomiasis among School-age children in Ogun State was conducted in this study. Midday urine samples were collected from 1,812 school-age children from ten selected Local Government Areas in Ogun State and were examined for the presence of haematuria (blood in urine) and Schistosoma haematobium ova. Out of the 1812 school-children examined, 92 (5.1%) tested positive for haematuria and 455 (25.1%) also tested positive for the presence of Schistosome ova. The highest infection prevalence rate (12.9%) was among female students infected with the parasite. The age group 10-12years had the highest rate of infection (12.2%), while the group 4-6 years had the lowest (1.3%) in the study areas. Therefore, urinary schistosomiasis is a major disease of major public health concern in Ogun State that requires prompt attention from relevant government and non-governmental agencies.
... Although the 3-30-300 rule allows the use of vegetation cover as an alternative indicator in areas not conducive to large-scale tree growth, future studies should still prioritize trees (Konijnendijk, 2021(Konijnendijk, , 2022. Meanwhile, the utilization of geospatial data can only approximate the evaluation of 3-30-300, the vertical imagery fails to capture true window visual information, the remote sensing vegetation index can only provide a proxy estimate rather than the exact number of tree canopies or area, and the POI as a focus of the greenspace probably suffers omissions (Hamm et al., 2015;Araujo Navas et al., 2016). Detailed canopy information is urgently needed for future studies related to the 3-30-300 rule. ...
... The use of geostatistical and spatial modeling has generated interest for its capacity to evaluate and map areas that may be endemic for schistosomiasis where there is limited surveillance or prevalence data [26][27][28], and has even been demonstrated to be a viable and cost-effective method of mapping schistosomiasis prevalence in certain settings (29). Regression techniques have additionally been used to estimate relationships between survey-based schistosomiasis prevalence and socio-ecological factors, and to predict prevalence at the un-sampled locations [30,31]. Some of these ecological factors, which have been shown to associate with the presence of schistosomiasis, are freely accessible and fairly well documented, and include distance to water bodies or wetlands, temperature, rainfalls, and altitude [32]. ...
... In subsequent modeling, it will be important to find a way to account for past PC coverage, particularly when sub-district MDA starts to become more commonly used in Tanzania. Further limitations of the study include the extraction and aggregation of data from different sources with varying timeframes, scales and methods, which may have reduced the accuracy of some of the predictions [31]. Additionally, the modeling approach used may have led to an underestimation of standard errors in the ZIP model, however, since the model did not exclude covariates based on their univariate associations, but rather the overall predictive accuracy of the model, it is unlikely this would have altered the variable composition of the geostatistical models. ...
Introduction
Schistosomiasis is a parasitic disease in Tanzania affecting over 50% of the population. Current control strategies involve mass drug administration (MDA) campaigns at the district level, which have led to problems of over- and under-treatment in different areas. WHO guidelines have called for more targeted MDA to circumvent these problems, however a scarcity of prevalence data inhibits decision makers from prioritizing sub-district areas for MDA. This study demonstrated how geostatistics can be used to inform planning for targeted MDA.
Methods
Geostatistical sub-district (ward-level) prevalence estimates were generated through combining a zero-inflated poisson model and kriging approach (regression kriging). To make predictions, the model used prevalence survey data collected in 2021 of 17,400 school children in six regions of Tanzania, along with several open source ecological and socio-demographic variables with known associations with schistosomiasis.
Results
The model results show that regression kriging can be used to effectively predict the ward level parasite prevalence of the two species of Schistosoma endemic to the study area. Kriging was found to further improve the regression model fit, with an adjusted R-squared value of 0.51 and 0.32 for intestinal and urogenital schistosomiasis, respectively. Targeted treatment based on model predictions would represent a shift in treatment away from 193 wards estimated to be over-treated to 149 wards that would have been omitted from the district level MDA.
Conclusions
Geostatistical models can help to support NTD program efficiency and reduce disease transmission by facilitating WHO recommended targeted MDA treatment through provision of prevalence estimates where data is scarce.
... The disease is common in resource poor locations and it has been established that groups whose economic livelihoods are as a consequence dependent on natural water bodies are at risk of infection. In this respect, women and children are particularly at greater risk of infection since they most commonly bath, fetch water and carry out household tasks in and near fresh water bodies (Manyangadze et al., 2016;Navas et al., 2016;Manyeh, 2021). Furthermore, this greater risk of infection among such groups is true for all Sub-Saharan African countries and is attributed mainly to risky water practices, poor sanitation, and lack of knowledge, negative attitudes and beliefs about schistosomiasis (Sacolo et al., 2018;UNAIDS, 2019). ...
Cryptosporidium and Giardia are significant causes of diarrhea and lungs illness. Adequate knowledge of the molecular diversity and geographical distribution of these parasites and the environmental and climatic variables that influence their prevalence is important for effective control of infection in at-risk populations, yet relatively little is known about the epidemiology of these parasites, globally. This review will confirm that Cryptosporidium is associated with moderate to severe diarrhea and increased mortality in the world and both parasites negatively affect child growth and development. Malnutrition and HIV status are also important contributors to the prevalence of Cryptosporidium and Giardia worldwide. Molecular typing of both parasites in humans, domestic animals and wildlife to date indicates a complex picture of both anthroponotic, zoonotic, and spill-back transmission cycles that require further investigation. For Cryptosporidium, the only available drug (Nitazoxanide) is ineffective in HIV and malnourished individuals and therefore more effective drugs are a high priority. Several classes of drugs with good efficacy exist for Giardia, but dosing regimens are suboptimal and emerging resistance threatens clinical utility. Climate change and population growth are also predicted to increase both malnutrition and the prevalence of these parasites in water sources. Dedicated and co-ordinate commitments from African governments involving “One Health” initiatives with multidisciplinary teams of veterinarians, microbiologist, medical workers, relevant government authorities, and public health specialists working
together are essential to control and prevent the burden of diseases caused by these parasites.
... The disease is common in resource poor locations and it has been established that groups whose economic livelihoods are as a consequence dependent on natural water bodies are at risk of infection. In this respect, women and children are particularly at greater risk of infection since they most commonly bath, fetch water and carry out household tasks in and near fresh water bodies (Manyangadze et al., 2016;Navas et al., 2016;Manyeh, 2021). Furthermore, this greater risk of infection among such groups is true for all Sub-Saharan African countries and is attributed mainly to risky water practices, poor sanitation, and lack of knowledge, negative attitudes and beliefs about schistosomiasis (Sacolo et al., 2018;UNAIDS, 2019). ...
Cryptosporidium and Giardia are significant causes of diarrhea and lungs illness. Adequate knowledge of the molecular diversity and geographical distribution of these parasites and the environmental and climatic variables that influence their prevalence is important for effective control of infection in at-risk populations, yet relatively little is known about the epidemiology of these parasites, globally. This review will confirm that Cryptosporidium is associated with moderate to severe diarrhea and increased mortality in the world and both parasites negatively affect child growth and development. Malnutrition and HIV status are also important contributors to the prevalence of Cryptosporidium and Giardia worldwide. Molecular typing of both parasites in humans, domestic animals and wildlife to date indicates a complex picture of both anthroponotic, zoonotic, and spill-back transmission cycles that require further investigation. For Cryptosporidium, the only available drug (Nitazoxanide) is ineffective in HIV and malnourished individuals and therefore more effective drugs are a high priority. Several classes of drugs with good efficacy exist for Giardia, but dosing regimens are suboptimal and emerging resistance threatens clinical utility. Climate change and population growth are also predicted to increase both malnutrition and the prevalence of these parasites in water sources. Dedicated and co-ordinate commitments from African governments involving “One Health” initiatives with multidisciplinary teams of veterinarians, microbiologist, medical workers, relevant government authorities, and public health specialists working
together are essential to control and prevent the burden of diseases caused by these parasites.
... The first applied an unsupervised machine learning technique to a clustering of S. stercoralis and S. fuelleborni genotypes in humans and dogs, while the other used a supervised machine learning model to demonstrate an association between the presence of gastrointestinal parasites (including Strongyloides) and the gut microbiome composition of a Cameroonian population [48,49]. However, the uncertainties that can lead to imprecision or inaccuracy within such mathematical models of soil-transmitted helminth infections should be carefully delineated, considered, and estimated, with a previous meta-analysis highlighting deficiencies in this regard in the studies that they analyzed [50]. The sources of uncertainty impacting Strongyloides epidemiologic modeling include not only imperfections in the sampling methods and the limitations of the diagnostic testing used, which can cause incorrect disease state assignments, but also epistemic biological factors such as the heterogeneity of detectability of the Strongyloides in different hosts, variations in the distribution and intensity of Strongyloides organisms among host populations, and the impact of host demographic factors. ...
Strongyloides stercoralis is a soil transmitted helminth endemic to tropical and subtropical areas that can persist for decades in immunocompetent human hosts as a chronic asymptomatic infection. The use of corticosteroids, a mainstay of treatment for patients hospitalized with severe coronavirus disease (COVID-19), can trigger a life-threatening Strongyloides hyperinfection syndrome and disseminated disease. We identified 22 previously published cases of strongyloidiasis occurring in individuals with COVID-19, with one death reported among the seven patients who had Strongyloides hyperinfection syndrome. A total of seventeen patients had previously received corticosteroids, and of the five with no prior corticosteroid use, one presented with hyperinfection syndrome. We identify the key challenges in the diagnosis and treatment of Strongyloides within the context of COVID-19, including our imprecise knowledge of the global distribution of Strongyloides, the overlapping symptoms and signs of COVID-19 and Strongyloides hyperinfection syndrome, the limited utility of eosinophilia as a clinical marker for strongyloidiasis in this setting, the lack of validated algorithms to screen for Strongyloides prior to corticosteroid use, and the paucity of treatment options for critically ill patients with COVID-19 who cannot take oral ivermectin. Future research should focus on improved diagnostic methods and population prevalence estimates, optimizing the approaches for Strongyloides screening in persons with COVID-19 (including clinical trial participants and strategies for resource-limited settings) and better defining the role of pre-emptive treatment.
... The uncertainty in model results also reflects the distribution of sampling points; visualisation of this uncertainty allows prioritisation of areas for future surveys. This has important implications both when planning surveillance and when allocating treatment at larger administrative units, as is commonly done for mass drug administration [49]. ...
Background
As prevalence decreases in pre-elimination settings, identifying the spatial distribution of remaining infections to target control measures becomes increasingly challenging. By measuring multiple antibody responses indicative of past exposure to different pathogens, integrated serological surveys enable simultaneous characterisation of residual transmission of multiple pathogens.
Methodology/Principal findings
Here, we combine integrated serological surveys with geostatistical modelling and remote sensing-derived environmental data to estimate the spatial distribution of exposure to multiple diseases in children in Northern Ghana. The study utilised the trachoma surveillance survey platform (cross-sectional two-stage cluster-sampled surveys) to collect information on additional identified diseases at different stages of elimination with minimal additional cost. Geostatistical modelling of serological data allowed identification of areas with high probabilities of recent exposure to diseases of interest, including areas previously unknown to control programmes. We additionally demonstrate how serological surveys can be used to identify areas with exposure to multiple diseases and to prioritise areas with high uncertainty for future surveys. Modelled estimates of cluster-level prevalence were strongly correlated with more operationally feasible metrics of antibody responses.
Conclusions/Significance
This study demonstrates the potential of integrated serological surveillance to characterise spatial distributions of exposure to multiple pathogens in low transmission and elimination settings when the probability of detecting infections is low.
... MDA campaigns targeting villages located closer to the lake may better reach SAC with higher rates of parasite exposure but, not necessarily, with a higher intensity of infection. There is a need to conduct more focal, precision mapping to reduce the size of MDA implementation units and to better locate high-risk populations [45][46][47][48]. One remaining challenge to consider is the mobility of populations. ...
Background
The interaction of socio-demographic and ecological factors with Schistosoma mansoni (S. mansoni) infection risk by age and the household clustering of infections between individuals are poorly understood.
Methods
This study examined 1,832 individuals aged 5–90 years across 916 households in Mayuge District, Uganda. S. mansoni infection status and intensity were measured using Kato-Katz microscopy. Socio-demographic and ecological factors were examined as predictors of infection status and intensity using logistic and negative binomial regression models, respectively, with standard errors clustered by household. A subgroup analysis of children was conducted to examine the correlation of infection status between children and their caretakers.
Findings
Infection varied within age groups based on the distance to Lake Victoria. Children aged 9–17 years and young adults aged 18–29 years who lived ≤0.50km from Lake Victoria were more likely to be infected compared to individuals of the same age who lived further away from the lake. Infections clustered within households. Children whose caretakers were heavily infected were 2.67 times more likely to be infected.
Conclusion
These findings demonstrate the focality of schistosome transmission and its dependence on socio-demographic, ecological and household factors. Future research should investigate the sampling of households within communities as a means of progressing towards precision mapping of S. mansoni infections.
... These populations are living in areas that have a low socioeconomic status with limited access to clean water and adequate sanitation. In most of the schistosomiasis endemic countries, people who have frequent contact with infected natural water bodies, because of the nature of their work are at a greater risk of infection [4]. The high Schistosoma infection risk among these groups is mainly due to risky water contact practices, poor sanitation, and lack of knowledge, and misconceptions about schistosomiasis [5]. ...
Background
Understanding the health behavior of the target population is crucial for sustainable schistosomiasis control. The aim of this study was to assess schistosomiasis related levels of knowledge, attitude, and practices of communities in lowland areas of western Ethiopia, where schistosomiasis is endemic.
Methods
A community-based multilevel triangulation mixed-methods design was conducted in three schistosomiasis endemic villages in the Abbey and Didessa valleys of the Benishangul Gumuz Region of Western Ethiopia, where mass drug administration (MDA) was done 30 years back and again the last 5 years. A structured survey questionnaire, in-depth interviews, focused group discussions, and observation was conducted to assess levels of knowledge, attitude, and practices related to schistosomiasis in the communities.
Results
Among the survey participants, 13% reported having heard of schistosomiasis, locally called Pecka (meaning worm). The majority of this 13% believe that schistosomiasis is caused by the biting of the worm Pecka, while others say drinking dirty water is the cause of infection, or they didn’t know what the cause is. A majority of respondents answered “I don’t know” to most of the questions about established knowledge of schistosomiasis. Male participants and students were more aware of schistosomiasis than their counterparts, and awareness increased with the educational level. Only one participant perceived that schistosomiasis was a serious disease. There were negative attitudes and misconceptions about the drug used in the mass treatment and many complaints were raised related to the size of the tablet and its side effects. There was no local budget and specific plan to prevent and control the disease. Local health personnel had insufficient knowledge about schistosomiasis, and the diagnosis and treatment capacities of local health institutions were poor.
Conclusion
In the current research area, schistosomiasis prevention and control recommendations should be redesigned to change the knowledge, attitudes, and practices of the community and local health workers. It is also necessary to have the local budget and trained manpower in order to diagnose and treat schistosomiasis locally. There is a great need to have a safer Praziquantel pediatric formulation.
