Environmental Predictors of Schistosomiasis Persistent Hotspots following Mass Treatment with Praziquantel

Diterpenoids with Schistosomula-Killing and Anti-Fibrosis Activities In Vitro from the Leaves of Croton tiglium

The leaves of C. tiglium have been comprehensively researched for their structurally novel bioactive natural compounds, especially those with anti-schistosomiasis liver fibrosis activity, because ethyl acetate extract, which can be extracted from the leaves of C. tiglium, has good anti-schistosomiasis liver fibrosis effects. One new tigliane-type diterpene, 20-acetyl-13-O-(2-metyl)butyryl-phorbol (1), and nine known (2-10) analogues were isolated from the leaves of C. tiglium. Their structures were elucidated on the basis of spectroscopic analysis and ECD analysis. All diterpenoids had a stronger insecticidal effect on schistosomula, and compounds 2, 4, and 10 had good anti-liver-fibrosis effects. Furthermore, compared with the model group, compound 2 significantly downregulated the protein and mRNA expression of COL-I, COL-III, α-SMA, and TGF-β1 on TGF-β1-induced liver fibrosis in LX-2 cells. Meanwhile, compound 2 also regulated the expression of TGF-β/Smad-pathway-related proteins. The results suggest that diterpenoids from C. tiglium may serve as potential schistosomula-killing and anti-liver-fibrosis agents in the future.

Defining schistosomiasis hotspots based on literature and shareholder interviews

The World Health Organization (WHO) recently proposed a new operational definition which designates communities with ≥10% prevalence of Schistosoma spp. infection as a persistent hotspot, when, after at least two rounds of high-coverage annual preventive chemotherapy, there is a lack of appropriate reduction. However, inconsistencies and challenges from both biological and operational perspectives remain, making the prescriptive use of this definition difficult. Here, we present a comprehensive analysis of the use of the term 'hotspot' across schistosomiasis research over time, including both literature searches and opinions from a range of stakeholders, to assess the utility and generalisability of the new WHO definition of a persistent hotspot. Importantly, we propose an updated definition based on our analyses.

Schistosoma Infection Burden and Risk Factors among School-Aged Children in a Rural Area of the Democratic Republic of the Congo

Despite continuous efforts to control schistosomiasis (SCH) in the Democratic Republic of the Congo (DRC), it still poses a significant challenge. In order to enhance control measures, additional research is necessary. This study documents the burden of SCH infection and its predictors in a rural area of the DRC. We conducted a household cross-sectional study from June to August 2021 among 480 school-aged children (SAC) aged 5-15 years living in a rural area of Kisangi, in the southwest DRC. We collected and examined stool, urine, and blood samples of each child. Additionally, we obtained data on anthropometry, socio-demographics, household information, and individual water contact behaviors. The overall prevalence of SCH infection was 55.8% (95% CI: 51.4-60.3), with prevalences of 41% (95% CI: 36.6-45.5), 36.3% (95% CI: 31.9-40.6), and 38.4% (95% CI: 32.6-44.3) for S. haematobium and S. mansoni infections and both infections, respectively. Among those with SCH infection, most had a light (67.5%) or heavy (51.7%) infection intensity. The geometric mean egg count was 16.6 EP 10 mL (95% CI: 12.9-21.3) for S. haematobium and 390.2 EPG (95% CI: 300.2-507.3) for S. mansoni. However, age (10 years and above (aOR: 2.1; 95% CI: 1.5-3.1; p < 0.001)) was an independent risk factor for SCH infection. The overall prevalence of malaria infection was 16.9% (95% CI: 13.5-20.2), that of stunting was 28.7% (95% CI: 24.7-32.8), that of underweight was 17.1% (95% CI: 12.8-21.4), and that of thinness was 7.1% (95% CI: 4.8-9.4). Anemia was prevalent at 49.4% (95% CI: 44.9-5), and the median Hb level of all participants was 11.6 g/dL (IQR: 10.5-12.6 g/dL). Anemia was strongly associated with SCH infection (aOR: 3.4; 95% CI: 2.3-5.1; p < 0.001) yet there was no association with the risk for malaria infection (aOR: 1.0; 95% CI: 0.6-1.8; p = 0.563). In addition, the risk of anemia increased with heavy infection intensities (p < 0.026 and p < 0.013 for S. haematobium and S. mansoni, respectively). However, stunting had a protective factor for anemia (aOR: 0.3; 95% CI: 0.2-0.4; p < 0.001). To conclude, SCH infection was widespread among the SAC and strongly linked to anemia. These results provide evidence of the hyperendemicity of infection in the study area, which requires preventative measures such as chemotherapy to reduce the schistosomiasis-associated morbidity, and micronutrient supplements to avoid anemia.

Open-source environmental data as an alternative to snail surveys to assess schistosomiasis risk in areas approaching elimination

BACKGROUND

Although the presence of intermediate snails is a necessary condition for local schistosomiasis transmission to occur, using them as surveillance targets in areas approaching elimination is challenging because the patchy and dynamic quality of snail host habitats makes collecting and testing snails labor-intensive. Meanwhile, geospatial analyses that rely on remotely sensed data are becoming popular tools for identifying environmental conditions that contribute to pathogen emergence and persistence.

METHODS

In this study, we assessed whether open-source environmental data can be used to predict the presence of human Schistosoma japonicum infections among households with a similar or improved degree of accuracy compared to prediction models developed using data from comprehensive snail surveys. To do this, we used infection data collected from rural communities in Southwestern China in 2016 to develop and compare the predictive performance of two Random Forest machine learning models: one built using snail survey data, and one using open-source environmental data.

RESULTS

The environmental data models outperformed the snail data models in predicting household S. japonicum infection with an estimated accuracy and Cohen's kappa value of 0.89 and 0.49, respectively, in the environmental model, compared to an accuracy and kappa of 0.86 and 0.37 for the snail model. The Normalized Difference in Water Index (an indicator of surface water presence) within half to one kilometer of the home and the distance from the home to the nearest road were among the top performing predictors in our final model. Homes were more likely to have infected residents if they were further from roads, or nearer to waterways.

CONCLUSION

Our results suggest that in low-transmission environments, leveraging open-source environmental data can yield more accurate identification of pockets of human infection than using snail surveys. Furthermore, the variable importance measures from our models point to aspects of the local environment that may indicate increased risk of schistosomiasis. For example, households were more likely to have infected residents if they were further from roads or were surrounded by more surface water, highlighting areas to target in future surveillance and control efforts.

Open-source environmental data as an alternative to snail surveys to assess schistosomiasis risk in areas approaching elimination

Background: Although the presence of intermediate snails is a necessary condition for local schistosomiasis transmission to occur, using them as surveillance targets in areas approaching elimination is challenging because the patchy and dynamic quality of snail host habitats makes collecting and testing snails labor-intensive. Meanwhile, geospatial analyses that rely on remotely sensed data are becoming popular tools for identifying environmental conditions that contribute to pathogen emergence and persistence. Methods: In this study, we assessed whether open-source environmental data can be used to predict the presence of human Schistosoma japonicum infections among households with a similar or improved degree of accuracy compared to prediction models developed using data from comprehensive snail surveys. To do this, we used infection data collected from rural communities in Southwestern China in 2016 to develop and compare the predictive performance of two Random Forest machine learning models: one built using snail survey data, and one using open-source environmental data. Results: The environmental data models outperformed the snail data models in predicting household S. japonicum infection with an estimated accuracy and Cohen’s kappa value of 0.89 and 0.49, respectively, in the environmental model, compared to an accuracy and kappa of 0.86 and 0.37 for the snail model. The Normalized Difference in Water Index (NDWI) within half to one kilometer of the home and the distance from the home to the nearest road were among the top performing predictors in our final model. Homes were more likely to have infected residents if they were further from roads, or nearer to waterways. Conclusion: Our results suggest that in low-transmission environments, investing in training geographic information systems professionals to leverage open-source environmental data could yield more accurate identification of pockets of human infection than using snail surveys. Furthermore, the variable importance measures from our models point to aspects of the local environment that may indicate increased risk of schistosomiasis. For example, households were more likely to have infected residents if they were further from roads or were surrounded by more surface water, highlighting areas to target in future surveillance and control efforts.

Predictive Risk Mapping of Schistosomiasis in Madagascar Using Ecological Niche Modeling and Precision Mapping

Schistosomiasis is a neglected tropical disease (NTD) found throughout tropical and subtropical Africa. In Madagascar, the condition is widespread and endemic in 74% of all administrative districts in the country. Despite the significant burden of the disease, high-resolution risk maps have yet to be produced to guide national control programs. This study used an ecological niche modeling (ENM) and precision mapping approach to estimate environmental suitability and disease transmission risk. The results show that suitability for schistosomiasis is widespread and covers 264,781 km2 (102,232 sq miles). Covariates of significance to the model were the accessibility to cities, distance to water, enhanced vegetation index (EVI), annual mean temperature, land surface temperature (LST), clay content, and annual precipitation. Disease transmission risk is greatest in the central highlands, tropical east coast, arid-southwest, and northwest. An estimated 14.9 million people could be at risk of schistosomiasis; 11.4 million reside in rural areas, while 3.5 million are in urban areas. This study provides valuable insight into the geography of schistosomiasis in Madagascar and its potential risk to human populations. Because of the focal nature of the disease, these maps can inform national surveillance programs while improving understanding of areas in need of medical interventions.

ABO Blood Groups Do Not Predict Schistosoma mansoni Infection Profiles in Highly Endemic Villages of Uganda

Schistosoma mansoni is a parasite which causes significant public-health issues, with over 240 million people infected globally. In Uganda alone, approximately 11.6 million people are affected. Despite over a decade of mass drug administration in this country, hyper-endemic hotspots persist, and individuals who are repeatedly heavily and rapidly reinfected are observed. Human blood-type antigens are known to play a role in the risk of infection for a variety of diseases, due to cross-reactivity between host antibodies and pathogenic antigens. There have been conflicting results on the effect of blood type on schistosomiasis infection and pathology. Moreover, the effect of blood type as a potential intrinsic host factor on S. mansoni prevalence, intensity, clearance, and reinfection dynamics and on co-infection risk remains unknown. Therefore, the epidemiological link between host blood type and S. mansoni infection dynamics was assessed in three hyper-endemic communities in Uganda. Longitudinal data incorporating repeated pretreatment S. mansoni infection intensities and clearance rates were used to analyse associations between blood groups in school-aged children. Soil-transmitted helminth coinfection status and biometric parameters were incorporated in a generalised linear mixed regression model including age, gender, and body mass index (BMI), which have previously been established as significant factors influencing the prevalence and intensity of schistosomiasis. The analysis revealed no associations between blood type and S. mansoni prevalence, infection intensity, clearance, reinfection, or coinfection. Variations in infection profiles were significantly different between the villages, and egg burden significantly decreased with age. While blood type has proven to be a predictor of several diseases, the data collected in this study indicate that it does not play a significant role in S. mansoni infection burdens in these high-endemicity communities.

Exposure, hazard, and vulnerability all contribute to Schistosoma haematobium re-infection in northern Senegal

Background

Infectious disease risk is driven by three interrelated components: exposure, hazard, and vulnerability. For schistosomiasis, exposure occurs through contact with water, which is often tied to daily activities. Water contact, however, does not imply risk unless the environmental hazard of snails and parasites is also present in the water. By increasing reliance on hazardous activities and environments, socio-economic vulnerability can hinder reductions in exposure to a hazard. We aimed to quantify the contributions of exposure, hazard, and vulnerability to the presence and intensity of Schistosoma haematobium re-infection.

Methodology/Principal findings

In 13 villages along the Senegal River, we collected parasitological data from 821 school-aged children, survey data from 411 households where those children resided, and ecological data from all 24 village water access sites. We fit mixed-effects logistic and negative binomial regressions with indices of exposure, hazard, and vulnerability as explanatory variables of Schistosoma haematobium presence and intensity, respectively, controlling for demographic variables. Using multi-model inference to calculate the relative importance of each component of risk, we found that hazard (Ʃw_{i =} 0.95) was the most important component of S. haematobium presence, followed by vulnerability (Ʃw_i = 0.91). Exposure (Ʃw_i = 1.00) was the most important component of S. haematobium intensity, followed by hazard (Ʃw_i = 0.77). Model averaging quantified associations between each infection outcome and indices of exposure, hazard, and vulnerability, revealing a positive association between hazard and infection presence (OR = 1.49, 95% CI 1.12, 1.97), and a positive association between exposure and infection intensity (RR 2.59–3.86, depending on the category; all 95% CIs above 1)

Conclusions/Significance

Our findings underscore the linkages between social (exposure and vulnerability) and environmental (hazard) processes in the acquisition and accumulation of S. haematobium infection. This approach highlights the importance of implementing both social and environmental interventions to complement mass drug administration.

While the impacts of natural hazards tend to be described in terms of social determinants such as exposure and vulnerability, the risk for infectious disease is often expressed in terms of environmental determinants without fully considering the socio-ecological processes that put people in contact with infective agents of disease. In the case of schistosomiasis, risk is determined by human interactions with freshwater environments where schistosome parasites circulate between people and aquatic snails. In this study, we quantified the relative contributions of exposure, hazard, and vulnerability to schistosome re-infection among schoolchildren in an endemic region of northern Senegal. We find that hazard and vulnerability influence whether a child becomes infected, while exposure and hazard influence the burden of worms once infection is acquired. Increasing numbers of worms is known to be positively associated with increasing severity of disease. Our findings underscore the importance of evaluating social and environmental determinants of disease simultaneously; omitting measures of exposure, hazard or vulnerability may limit our understanding of risk.

Schistosome infection in Senegal is associated with different spatial extents of risk and ecological drivers for Schistosoma haematobium and S. mansoni

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 (i) the area of remotely-sensed snail habitat across spatial extents ranging from 1 to 120 m from shorelines, and (ii) water access site size and shape characteristics. We compared the influence of snail habitat across spatial extents because, while snail sampling is traditionally done near shorelines, we hypothesized that snails further from shore also contribute to infection risk. We found that, controlling for demographic variables, human risk for S. haematobium infection was positively correlated with snail habitat when snail habitat was measured over a much greater radius from shore (45 m to 120 m) than usual. S. haematobium risk was also associated with large, open water access sites. However, S. mansoni infection risk was associated with small, sheltered water access sites, and was not positively correlated with snail habitat at any spatial sampling radius. Our findings highlight the need to consider different ecological and environmental factors driving the transmission of each schistosome species in co-endemic landscapes.

Schistosome parasites infect more than 200 million people worldwide, mainly in sub-Saharan Africa, where many people are at-risk for infection by multiple schistosome species simultaneously. To reduce the global burden of schistosomiasis, control of the parasites’ intermediate host–specific species of freshwater snails–has been elevated in priority to complement mass drug administration campaigns in endemic areas. To maximize the efficacy and efficiency of snail control efforts, a better understanding of where to target intermediate host snails is badly needed. This includes a better understanding of the spatial scale at which snails in the environment contribute to human infection risk, and, in co-endemic settings, how ecological determinants of infection risk vary by schistosome species. We used quantitative snail sampling and remotely-sensed data at 16 villages in the Senegal River Basin to compare and contrast ecological correlates and spatial scales of infection risk from freshwater snails that transmit Schistosoma haematobium versus S. mansoni. We found that infection risk for S. haematobium was associated with snail habitat at a larger spatial radius than is typically considered for schistosomiasis monitoring and control, whereas infection risk for S. mansoni was not positively correlated with snail habitat at any spatial sampling radius, but was associated with small water access sites enclosed by emergent vegetation. Our findings highlight the need to consider the different ecological and environmental factors driving the transmission of each schistosome species in co-endemic landscapes.

Effectiveness of mass treatment of Schistosoma mansoni infection in socially vulnerable areas of a state in northeastern Brazil, 2011-2014

Background

To assess the effectiveness of mass treatment of Schistosoma mansoni infection in socially vulnerable endemic areas in northeastern Brazil.

Method

An ecological study was conducted, in which 118 localities in 30 municipalities in the state of Pernambuco were screened before 2011 and in 2014 (after mass treatment). Information on the endemic baseline index, mass treatment coverage, socio-environmental conditions and social vulnerability index were used in the multiple correspondence analysis. One hundred fourteen thousand nine hundred eighty-seven people in 118 locations were examined.

Results

The first two dimensions of the multiple correspondence analysis represented 55.3% of the variability between locations. The human capital component of the social vulnerability index showed an association with the baseline endemicity index. There was a significant reduction in positivity for schistosomes. For two rounds, for every extra 1% of initial endemicity index, the fixed effect of 13.62% increased by 0.0003%, achieving at most 15.94%.

Conclusions

The mass treatment intervention helped to reduce transmission of schistosomiasis in areas of high endemicity. Thus, it can be recommended that application of mass treatment should be accompanied by other control actions, such as basic sanitation, monitoring of intermediate vectors and case surveillance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13690-021-00549-9.

Evaluation of prophylactic efficacy and safety of praziquantel-miltefosine nanocombination in experimental Schistosomiasis mansoni

The control of schistosomiasis depends exclusively on praziquantel (PZQ) monotherapy with treatment failure due to minor activity against the juvenile stage, re-infection and emerging drug resistance. Improving the antischistosomal therapeutic/prophylactic profile of PZQ is a sensible option to save the clinical benefits of the drug if achieved effectively and safely via a single oral dose. Recently, we developed praziquantel-miltefosine lipid nanocapsules (PZQ 250 mg/kg-MFS 20 mg/kg LNCs) as a nanotechnology-enabled novel drug combination with significant multistage activity against Schistosoma mansoni (S. mansoni) in a murine model. The present study aimed at providing a proof of concept of the chemoprophylactic effect of this nanocombination. A single oral dose of the nanocombination was administered to mice one and seven days before challenge infection with S. mansoni. The protective effect of the nanocombination was assessed parasitologically and histopathologically relative to LNCs singly-loaded with PZQ or MFS and non-treated infected controls. In addition, the safety of the nanocombination was assessed biochemically and histopathologically. Administration of the nanocombination one or seven days pre-infection resulted in a statistically significant reduction in mean worm burden and granulomas size associated with amelioration of hepatic pathology compared to infected non-treated control. Although, the prophylactic effect was significantly reduced upon administration seven days pre-infection compared to administration one day pre-infection, yet, it still exists. Results were explained based on the spectrum of activity of PZQ and MFS and their complementary pharmacokinetic (PK) profiles in addition to the effect of nanoencapsulation on these factors. The novel PZQ-MFS nanocombination offers valuable potentials in PZQ-based mass drug administration programmes by granting radical cure, preventing re-infection, and delaying development of resistance to the component drugs.

Molecular Tools and Schistosomiasis Transmission Elimination

Large-scale control efforts in sub-Saharan Africa may leave long-term lingering transmission. Large-scale screening of snail infection prevalence by loop-mediated isothermal amplification will enable accurate determination of man-to-snail transmission, as well as the effects of biota in snail habitat on host capacity and thus on snail-to-man transmission. Next-generation sequencing will enable identification of gut content of snails and thus their feeding preferences in hot spots and in non–hot spots, as well as for identification of attractive vegetation types for attracting snails to molluscicides.

Challenges in Protocol Development and Interpretation of the Schistosomiasis Consortium for Operational Research and Evaluation Intervention Studies

In 2010, the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) began the design of randomized controlled trials to compare different strategies for praziquantel mass drug administration, whether for gaining or sustaining control of schistosomiasis or for approaching local elimination of Schistosoma transmission. The goal of this operational research was to expand the evidence base for policy-making for regional and national control of schistosomiasis in sub-Saharan Africa. Over the 10-year period of its research programs, as SCORE operational research projects were implemented, their scope and scale posed important challenges in terms of research performance and the final interpretation of their results. The SCORE projects yielded valuable data on program-level effectiveness and strengths and weaknesses in performance, but in most of the trials, a greater-than-expected variation in community-level responses to assigned schedules of mass drug administration meant that identification of a dominant control strategy was not possible. This article critically reviews the impact of SCORE’s cluster randomized study design on performance and interpretation of large-scale operational research such as ours.