Transmission Dynamics Of Schistosomiasis Research Articles

Exploring the interplay between climate change and schistosomiasis transmission dynamics

Schistosomiasis, a neglected tropical disease caused by parasitic worms, poses a major public health challenge in economically disadvantaged regions, especially in Sub-Saharan Africa. Climate factors, such as temperature and rainfall patterns, play a crucial role in the transmission dynamics of the disease. This study presents a deterministic model that aims to evaluate the temporal and seasonal transmission dynamics of schistosomiasis by examining the influence of temperature and rainfall over time. Equilibrium states are examined to ascertain their existence and stability employing the center manifold theory, while the basic reproduction number is calculated using the next-generation technique. To validate the model's applicability, demographic and climatological data from Uganda, Kenya, and Tanzania, which are endemic East African countries situated in the tropical region, are utilized as a case study region. The findings of this study provide evidence that the transmission of schistosomiasis in human populations is significantly influenced by seasonal and monthly variations, with incidence rates varying across countries depending on the frequency of temperature and rainfall. Consequently, the region is marked by both schistosomiasis emergencies and re-emergences. Specifically, it is observed that monthly mean temperatures within the range of 22–27 °C create favorable conditions for the development of schistosomiasis and have a positive impact on the reproduction numbers. On the other hand, monthly maximum temperatures ranging from 27 to 33 °C have an adverse effect on transmission. Furthermore, through sensitivity analysis, it is projected that by the year 2050, factors such as the recruitment rate of snails, the presence of parasite egg-containing stools, and the rate of miracidia shedding per parasite egg will contribute significantly to the occurrence and control of schistosomiasis infections. This study highlights the significant influence of seasonal and monthly variations, driven by temperature and rainfall patterns, on the transmission dynamics of schistosomiasis. These findings underscore the importance of considering climate factors in the control and prevention strategies of schistosomiasis. Additionally, the projected impact of various factors on schistosomiasis infections by 2050 emphasizes the need for proactive measures to mitigate the disease's impact on vulnerable populations. Overall, this research provides valuable insights to anticipate future challenges and devise adaptive measures to address schistosomiasis transmission patterns.

Sampling collections and metadata of planorbidae (Mollusca: Gastropoda) in Brazil: a comprehensive analysis of the Oswaldo Cruz Institute’s Mollusk Collection from 1948 to 2023

Planorbidae comprises approximately 40 genera of freshwater gastropods, including roughly 250 species. Among the Planorbidae subfamilies, the significance of Planorbinae is due to its genus Biomphalaria, whose species are intermediate hosts of the trematode Schistosoma mansoni Sambon, 1907, which causes schistosomiasis in humans and animals. Here, we present the analysis of the dataset of Planorbidae housed in the Collection of Mollusks of the Oswaldo Cruz Institute, with a special focus on Biomphalaria species. This dataset includes 7,267 lots originating from 55 countries, representing 20 genera and 75 species collected from 1948 to 2023. Collections were performed in all regions of Brazil, comprising specimens from 26 states and the Federal District, particularly from the Southeast and Northeast. Within the dataset, Biomphalaria includes 3,926 lots of 31 species from 42 countries. These records will help improve our comprehension of schistosomiasis transmission dynamics and the geographic distributions of these medically important species.

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Modelling the Role of Treatment, Public Health Education, and Chemical Control Strategies on Transmission Dynamics of Schistosomiasis

In this study, a mathematical model for the transmission dynamics and control of schistosomiasis is studied using a system of nonlinear ordinary differential equations. The basic reproduction number ℛ 0 for the model is obtained, and its dependence on model parameters is discussed. Analytical results reveal that the disease-free equilibrium point is globally stable if and only if the basic reproduction number ℛ 0 < 1 , indicating that the disease would be wiped out of the community, and the endemic equilibrium point is globally stable if ℛ 0 > 1 and the disease would persist at the endemic steady state. Numerical simulations reveal that a combination of treatment, public health education, and chemical control intervention strategies significantly increased the number of susceptible human population and susceptible snail population while significantly decreasing the number of infected humans, miracidia, infected snails, and cercariae. The results further indicate that a combination of treatment, public health education, and chemical control intervention strategies can effectively manage the transmission of schistosomiasis in endemic areas.

On the mathematical modeling of schistosomiasis transmission dynamics with heterogeneous intermediate host

Schistosomiasis is a neglected disease affecting almost every region of the world, with its endemicity mainly experience in sub-Saharan Africa. It remains difficult to eradicate due to heterogeneity associated with its transmission mode. A mathematical model of Schistosomiasis integrating heterogeneous host transmission pathways is thus formulated and analyzed to investigate the impact of the disease in the human population. Mathematical analyses are presented, including establishing the existence and uniqueness of solutions, computation of the model equilibria, and the basic reproduction number (R0). Stability analyses of the model equilibrium states show that disease-free and endemic equilibrium points are locally and globally asymptotically stable whenever R0 < 1 and R0>1, respectively. Additionally, bifurcation analysis is carried out to establish the existence of a forward bifurcation around R0 = 1. Using Latin-hypercube sampling, global sensitivity analysis was performed to examine and investigate the most significant model parameters in R0 which drives the infection. The sensitivity analysis result indicates that the snail's natural death rate, cercariae, and miracidia decay rates are the most influential parameters. Furthermore, numerical simulations of the model were done to show time series plots, phase portraits, and 3-D representations of the model and also to visualize the impact of the most sensitive parameters on the disease dynamics. Our numerical findings suggest that reducing the snail population will directly reduce Schistosomiasis transmission within the human population and thus lead to its eradication.

A Mathematical Model for the Transmission Dynamics of Schistosomiasis with Treatment

A Mathematical Model for the Transmission Dynamics of Schistosomiasis with Treatment

Mathematical Analysis and Optimal Control of Schistosomiasis Transmission Model

Schistosomiasis, a health challenge in many communities, is prevalent as the rate of infection is one in every thirty individuals. In this work, a deterministic model for schistosomiasis transmission dynamics is studied. The stability properties of equilibrium states, disease-free and endemic equilibria are established in terms of the basic reproduction number, R_0. The sensitivity analysis of R_0 with respect to the model parameters is carried out using Partial rank correlation coefficients (PRCCs). The optimal control model with control measures, public health education, diagnosis and treatment and snail control, is formulated and its optimality system is derived using Pontragyin's maximum Principle. Simulation results showed that simultaneous implementation of public health education, diagnosis and treatment and snail control will reduce the burden of the schistosomiasis infection in the population. However due to toxicity of some snail controls to other aquatic bodies and difficulty to single out the chemical control that will focus only on the snail population even though snails are special food in Africa, it is preferable to implement public health education and diagnosis and treatment simultaneously in order to eradicate schistosomiasis transmission in the affected regions.

Schistosoma mansoni miracidia: revisiting motility and survival parameters for improved computational modelling.

Schistosoma mansoni is the main causative agent of intestinal schistosomiasis which affects millions of people worldwide. At the larval stage, miracidia are released into bodies of water where they utilize their motility to successfully infect their intermediate host, snails. Here, we revisit the motility and survival of S. mansoni miracidia throughout its life span. Briefly, miracidia motility was monitored at 30-min and 60-min intervals under the presence/absence of natural/artificial light. Based on a subjective evaluation of activity, body shape and transparency, 6 categories of miracidia activity were established from its fully active stage to its immobile larva stage. The estimated life span of miracidia was 5.8 and 3.5 h in the experiments with 60-min and 30-min observation intervals, respectively. Death was defined by an absence of cilia and body movement. When mobility was used as a proxy for infectivity, infective miracidia were detected at 2.5 and 4.5 h, respectively. The present miracidia motility and survival re-evaluation supports parameters optimization for computational modelling of schistosomiasis transmission dynamics. Target control interventions, especially at late stages next to transmission interruption, may greatly benefit from improved modelling studies.

Public Health Policy Pillars for the Sustainable Elimination of Zoonotic Schistosomiasis

Schistosomiasis is a parasitic disease acquired through contact with contaminated freshwater. The definitive hosts are terrestrial mammals, including humans, with some Schistosoma species crossing the animal-human boundary through zoonotic transmission. An estimated 12 million people live at risk of zoonotic schistosomiasis caused by Schistosoma japonicum and Schistosoma mekongi, largely in the World Health Organization’s Western Pacific Region and in Indonesia. Mathematical models have played a vital role in our understanding of the biology, transmission, and impact of intervention strategies, however, these have mostly focused on non-zoonotic Schistosoma species. Whilst these non-zoonotic-based models capture some aspects of zoonotic schistosomiasis transmission dynamics, the commonly-used frameworks are yet to adequately capture the complex epi-ecology of multi-host zoonotic transmission. However, overcoming these knowledge gaps goes beyond transmission dynamics modelling. To improve model utility and enhance zoonotic schistosomiasis control programmes, we highlight three pillars that we believe are vital to sustainable interventions at the implementation (community) and policy-level, and discuss the pillars in the context of a One-Health approach, recognising the interconnection between humans, animals and their shared environment. These pillars are: (1) human and animal epi-ecological understanding; (2) economic considerations (such as treatment costs and animal losses); and (3) sociological understanding, including inter- and intra-human and animal interactions. These pillars must be built on a strong foundation of trust, support and commitment of stakeholders and involved institutions.

Mathematical Modeling and Analysis of Transmission Dynamics and Control of Schistosomiasis

This paper presents a mathematical model that describes the transmission dynamics of schistosomiasis for humans, snails, and the free living miracidia and cercariae. The model incorporates the treated compartment and a preventive factor due to water sanitation and hygiene (WASH) for the human subpopulation. A qualitative analysis was performed to examine the invariant regions, positivity of solutions, and disease equilibrium points together with their stabilities. The basic reproduction number, R 0 , is computed and used as a threshold value to determine the existence and stability of the equilibrium points. It is established that, under a specific condition, the disease-free equilibrium exists and there is a unique endemic equilibrium when R 0 > 1 . It is shown that the disease-free equilibrium point is both locally and globally asymptotically stable provided R 0 < 1 , and the unique endemic equilibrium point is locally asymptotically stable whenever R 0 > 1 using the concept of the Center Manifold Theory. A numerical simulation carried out showed that at R 0 = 1 , the model exhibits a forward bifurcation which, thus, validates the analytic results. Numerical analyses of the control strategies were performed and discussed. Further, a sensitivity analysis of R 0 was carried out to determine the contribution of the main parameters towards the die out of the disease. Finally, the effects that these parameters have on the infected humans were numerically examined, and the results indicated that combined application of treatment and WASH will be effective in eradicating schistosomiasis.

Spatial and seasonal distribution of Bulinus globosus and Biomphalaria pfeifferi in Ingwavuma, uMkhanyakude district, KwaZulu-Natal, South Africa: Implications for schistosomiasis transmission at micro-geographical scale

BackgroundSchsistosomiasis is endemic in sub-Saharan Africa. It is transmitted by intermediate host snails such as Bulinus and Biomphalaria. An understanding of the abundance and distribution of snail vectors is important in designing control strategies. This study describes the spatial and seasonal variation of B. globosus and Bio. pfeifferi and their schistosome infection rates between May 2014 and May 2015 in Ingwavuma, uMkhanyakude district, KwaZulu-Natal province, South Africa.MethodsSnail sampling was done on 16 sites once every month by two people for 30 min at each site using the scooping and handpicking methods. Snails collected from each site were screened for schistosome mammalian cercariae by the shedding method. The negative binomial generalised linear mixed model (glmm) was used to determine the relationship between abundances of the intermediate host snails and climatic factors [rainfall, land surface temperatures (LST), seasons, habitats, sampling sites and water physico-chemical parameters including pH and dissolved oxygen (DO)].ResultsIn total, 1846 schistosomiasis intermediate host snails were collected during the study period. Biompharia pfeifferi was more abundant (53.36%, n = 985) compared to B. globosus (46.64%, n = 861). Bulinus globosus was recorded at 12 sites (75%) and Bio. pfeifferi was present at 7 sites (43.8%). Biompharia pfeifferi cohabited with B. globosus at all the sites it was present. High numbers of Bio. pfeifferi (n = 872, 88.5%) and B. globosus (n = 705, 81.9%) were found between winter and mid-spring. Monthly rainfall showed a statistically significant negative relationship with the abundance of B. globosus (p < 0.05). Dissolved oxygen (DO) had a statistically significant positive relationship with the abundance of Bio. pfeifferi (p < 0.05) while (LST) had a statistically significant negative relationship (p < 0.05). More B. globosus (8.9%, n = 861) were shedding schistosome mammalian cercariae compared to Bio. pfeifferi (0.1%, n = 985) confirming the already documented high prevalence of S. haematobium in Ingwavuma compared to S. mansoni.ConclusionResults of this study provide updated information on the distribution of schistosomiasis intermediate host snails in the study area and contributes towards the understanding of the transmission dynamics of schistosomiasis at the micro-geographical scale in this area.Graphical

OPTIMAL CONTROL ANALYSIS OF A HUMAN–BOVINE SCHISTOSOMIASIS MODEL

We formulate and analyze a deterministic mathematical model for the transmission dynamics of schistosomiasis with treatment of both humans and bovines and mollu-sciciding of the contaminated environment. The model effective reproduction number is derived and analytical results show that the disease-free and endemic equilibria are both locally and globally asymptotically stable. Pontryagin’s Maximum Principle which uses both Lagrangian and Hamiltonian principles with respect to a time-dependent constant is used to establish the existence of the optimal control problem and to derive the necessary conditions for optimal control of the disease. Mollusciciding of the contaminated environment has a major impact on disease control. However, combining it with treatment could help mitigate the spread of the disease compared to applying each control measure individually. Numerical simulations are performed to support theoretical results.

A THEORETICAL STUDY ON SCHISTOSOMIASIS INFECTION MODEL: APPLICATION OF BIOLOGICAL OPTIMAL CONTROL

A general mathematical model for schistosomiasis is formulated that incorporates the miracidia and cercariae dynamics, since parasites play an important role in the transmission dynamics of schistosomiasis. This model is an extension of the study undertaken in Diaby etc [<span class="xref"><a href="#b6" ref-type="bibr">6</a></span>] concerning the evolution of a schistosomiasis infection. Meanwhile, optimal control theory is applied to the proposed model. In the first part of our analysis we describe and propose a complete mathematical analysis of a new mathematical model for schistosomiasis infection with fixed control for both drug and biological treatment. It also includes a net inflow of competitor snails into the aquatic region at the rate $ u $ per unit of time as control term. Schistosomiasis is associated with water resource development such as dams and irrigation schemes, where the snail is the intermediate host of the parasite breeds. The snail intermediate host breeds in slow-flowing or stagnant water. We establish a deterministic model to explore the role of biological control strategy. We derive the basic reproduction number $ \mathcal{R}_0 $ and establish that the global dynamics are completely determined by the values of $ \mathcal{R}_0 $. It is shown that the disease can be eradicated when $ \mathcal{R}_0 \leq 1 $. In the case where $ \mathcal{R}_0 &gt;1 $, we prove the existence, uniqueness and global asymptotic stability of an endemic equilibrium. We also show how the control $ u $ can be chosen in order to eradicate the disease. In the second part, we take the controls as time dependent and obtain the optimal control strategy to minimize both infected humans and snails populations. All the analytical results are verified by simulation works. Some important conclusions are given at the end of the paper.

Prevalence and distribution of schistosomiasis in human, livestock, and snail populations in northern Senegal: a One Health epidemiological study of a multi-host system

SummaryBackgroundSchistosomiasis is a neglected tropical disease of global medical and veterinary importance. As efforts to eliminate schistosomiasis as a public health problem and interrupt transmission gather momentum, the potential zoonotic risk posed by livestock Schistosoma species via viable hybridisation in sub-Saharan Africa have been largely overlooked. We aimed to investigate the prevalence, distribution, and multi-host, multiparasite transmission cycle of Haematobium group schistosomiasis in Senegal, West Africa.MethodsIn this epidemiological study, we carried out systematic surveys in definitive hosts (humans, cattle, sheep, and goats) and snail intermediate hosts, in 2016–18, in two areas of Northern Senegal: Richard Toll and Lac de Guiers, where transmission is perennial; and Barkedji and Linguère, where transmission is seasonal. The occurrence and distribution of Schistosoma species and hybrids were assessed by molecular analyses of parasitological specimens obtained from the different hosts. Children in the study villages aged 5–17 years and enrolled in school were selected from school registers. Adults (aged 18–78 years) were self-selecting volunteers. Livestock from the study villages in both areas were also randomly sampled, as were post-mortem samples from local abattoirs. Additionally, five malacological surveys of snail intermediate hosts were carried out at each site in open water sources used by the communities and their animals.FindingsIn May to August, 2016, we surveyed 375 children and 20 adults from Richard Toll and Lac de Guiers, and 201 children and 107 adults from Barkedji and Linguère; in October, 2017, to January, 2018, we surveyed 386 children and 88 adults from Richard Toll and Lac de Guiers, and 323 children and 85 adults from Barkedji and Linguère. In Richard Toll and Lac de Guiers the prevalence of urogenital schistosomiasis in children was estimated to be 87% (95% CI 80–95) in 2016 and 88% (82–95) in 2017–18. An estimated 63% (in 2016) and 72% (in 2017–18) of infected children were shedding Schistosoma haematobium–Schistosoma bovis hybrids. In adults in Richard Toll and Lac de Guiers, the prevalence of urogenital schistosomiasis was estimated to be 79% (52–97) in 2016 and 41% (30–54) in 2017–18, with 88% of infected samples containing S haematobium–S bovis hybrids. In Barkedji and Linguère the prevalence of urogenital schistosomiasis in children was estimated to be 30% (23–38) in 2016 and 42% (35–49) in 2017–18, with the proportion of infected children found to be shedding S haematobium–S bovis hybrid miracidia much lower than in Richard Toll and Lac de Guiers (11% in 2016 and 9% in 2017–18). In adults in Barkedji and Linguère, the prevalence of urogenital schistosomiasis was estimated to be 26% (17–36) in 2016 and 47% (34–60) in 2017–18, with 10% of infected samples containing S haematobium–S bovis hybrids. The prevalence of S bovis in the sympatric cattle population of Richard Toll and the Lac de Guiers was 92% (80–99), with S bovis also found in sheep (estimated prevalence 14% [5–31]) and goats (15% [5–33]). In Barkedji and Linguère the main schistosome species in livestock was Schistosoma curassoni, with an estimated prevalence of 73% (48–93) in sheep, 84% (61–98) in goats and 8% (2–24) in cattle. S haematobium–S bovis hybrids were not found in livestock. In Richard Toll and Lac de Guiers 35% of infected Bulinus spp snail intermediate hosts were found to be shedding S haematobium–S bovis hybrids (68% shedding S haematobium; 17% shedding S bovis); however, no snails were found to be shedding S haematobium hybrids in Barkedji and Linguère (29% shedding S haematobium; 71% shedding S curassoni).InterpretationOur findings suggest that hybrids originate in humans via zoonotic spillover from livestock populations, where schistosomiasis is co-endemic. Introgressive hybridisation, evolving host ranges, and wider ecosystem contexts could affect the transmission dynamics of schistosomiasis and other pathogens, demonstrating the need to consider control measures within a One Health framework.FundingZoonoses and Emerging Livestock Systems programme (UK Biotechnology and Biological Sciences Research Council, UK Department for International Development, UK Economic and Social Research Council, UK Medical Research Council, UK Natural Environment Research Council, and UK Defence Science and Technology Laboratory).

Mathematical Modeling for Schistosomiasis with Seasonal Influence: A Case Study in Hubei, China

In this paper, we investigate a time-delayed differential model of the transmission dynamics of schistosomiasis with seasonality. In order to study the influence of water temperature on egg hatchin...

Insights from quantitative and mathematical modelling on the proposed WHO 2030 goal for schistosomiasis.

Schistosomiasis remains one of the neglected tropical diseases (NTDs) impacting millions of people around the world. The World Health Organization (WHO) recently proposed a goal of elimination as a public health problem (EPHP) for schistosomiasis to be reached by 2030. Current WHO treatment guidelines for achieving EPHP focus on targeting school-aged children. The NTD Modelling Consortium has developed mathematical models to study schistosomiasis transmission dynamics and the impact of control measures. Our modelling insights on Schistosoma mansoni have shown that EPHP is likely to be attainable in low to moderate prevalence settings using the current guidelines. However, as prevalence rises within high prevalence settings, EPHP is less likely to be achieved unless both school-aged children and adults are treated (with coverage levels increasing with the adult burden of infection). We highlight the challenges that are faced by treatment programmes, such as non-adherence to treatment and resurgence, which can hinder progress towards achieving and maintaining EPHP. Additionally, even though EPHP may be reached, prevalence can still be high due to persisting infections. Therefore, without interruption of transmission, treatment will likely have to continue to maintain EPHP. Further modelling work is being carried out, including extending our results to S. haematobium. By providing these modelling insights, we aim to inform discussions on the goals and treatment guidelines for schistosomiasis.

Insights from quantitative and mathematical modelling on the proposed WHO 2030 goal for schistosomiasis.

Schistosomiasis remains one of the neglected tropical diseases (NTDs) impacting millions of people around the world. The World Health Organization (WHO) recently proposed a goal of elimination as a public health problem (EPHP) for schistosomiasis to be reached by 2030. Current WHO treatment guidelines for achieving EPHP focus on targeting school-aged children. The NTD Modelling Consortium has developed mathematical models to study schistosomiasis transmission dynamics and the impact of control measures. Our modelling insights on Schistosoma mansoni have shown that EPHP is likely to be attainable in low to moderate prevalence settings using the current guidelines. However, as prevalence rises within higher settings, EPHP is less likely to be achieved unless both school-aged children and adults are treated (with coverage levels increasing with the adult burden of infection). We highlight the challenges that are faced by treatment programmes, such as non-adherence to treatment and resurgence, which can hinder progress towards achieving and maintaining EPHP. Additionally, even though EPHP may be reached, prevalence can still be high due to persisting infections. Therefore, without elimination of transmission, treatment will likely have to continue to maintain EPHP. Further modelling work is being carried out, including extending our results to S. haematobium. By providing these modelling insights, we aim to inform discussions on the goals and treatment guidelines for schistosomiasis.

Population genetics of Oncomelania hupensis snails, intermediate hosts of Schistosoma japonium, from emerging, re-emerging or established habitats within China

Schistosomiasis remains one of the world’s most significant neglected tropical diseases, second only to malaria in terms of socioeconomic impact. In 2014, China proposed the goal of schistosomiasis japonicum elimination by 2025. However, one major challenge is the widely distributed, and in certain cases potentially increasing, habitats of Oncomelania hupensis, the snail intermediate hosts of S. japonicum. Therefore, an understanding of population genetics of O. hupensis in new or re-emerged habitats, together with that of the established habitats with snail persistence, would be valuable in controlling and predicting the future transmission dynamics of schistosomiasis in China. Using nine microsatellite loci, we conducted population genetic analyses of snails sampled from one habitat where snails were detected for the first time, one (previously eliminated) habitat with re-emerged snails, and one habitat with established snail persistence. Results showed lower diversities, in terms of number of observed alleles per locus (Na), number of effective alleles per locus (NeA), observed (Ho) and expected heterozygosity (He), in snails from new or re-emerged snail habitats than from the habitat with snail persistence. The smallest effective population size was inferred in the re-emerged snail habitat, but the largest was in the new habitat rather than in the habitat with snail persistence. No bottleneck effects were detected in new or re-merged habitats. No or low sub-structure was inferred in new and persistent snail habitats. Snails from the three sites were clearly separated and low gene flow was estimated between sites. We propose that snails at the new habitat may have been introduced through immigration, whereas snails at the re-emerged habitat may be the consequence of those few snails remaining subsequently expanding through reproduction. We discuss our results in terms of their theoretical and applied implications.

Global Transmission Dynamics of a Schistosomiasis Model and Its Optimal Control

Drug treatment, snail control, cercariae control, improved sanitation and health education are the effective strategies which are used to control the schistosomiasis. In this paper, we consider a deterministic model for schistosomiasis transmission dynamics in order to explore the role of the several control strategies. The global stability of a schistosomiasis infection model that involves mating structure including male schistosomes, female schistosomes, paired schistosomes and snails is studied by constructing appropriate Lyapunov functions. We derive the basic reproduction number R0 for the deterministic model, and establish that the global dynamics are completely determined by the values of R0. We show that the disease can be eradicated when R0 ≤1; otherwise, the system is persistent. In the case where R0 >1, we prove the existence, uniqueness and global asymptotic stability of an endemic steady state. Sensitivity analysis and simulations are carried out in order to determine the relative importance of different control strategies for disease transmission and prevalence. Next, optimal control theory is applied to investigate the control strategies for eliminating schistosomiasis using time dependent controls. The characterization of the optimal control is carried out via the Pontryagins Maximum Principle. The simulation results demonstrate that the insecticide is important in the control of schistosomiasis.