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The geographical range of schistosomiasis is affected by the ecology of schistosome parasites and their obligate host snails, including their response to temperature. Previous models predicted schistosomiasis’ thermal optimum at 21.7°C, which is not compatible with the temperature in sub-Saharan Africa (SSA) regions where schistosomiasis is hyperendemic. We performed an extensive literature search for empirical data on the effect of temperature on physiological and epidemiological parameters regulating the free-living stages of S . mansoni and S . haematobium and their obligate host snails, i.e., Biomphalaria spp. and Bulinus spp., respectively. We derived nonlinear thermal responses fitted on these data to parameterize a mechanistic, process-based model of schistosomiasis. We then re-cast the basic reproduction number and the prevalence of schistosome infection as functions of temperature. We found that the thermal optima for transmission of S . mansoni and S . haematobium range between 23.1–27.3°C and 23.6–27.9°C (95% CI) respectively. We also found that the thermal optimum shifts toward higher temperatures as the human water contact rate increases with temperature. Our findings align with an extensive dataset of schistosomiasis prevalence in SSA. The refined nonlinear thermal-response model developed here suggests a more suitable current climate and a greater risk of increased transmission with future warming for more than half of the schistosomiasis suitable regions with mean annual temperature below the thermal optimum.

Schistosomiasis is a significant public health threat, and Oncomelania hupensis is the only intermediate host for schistosoma japonicum . We conducted 12-year monthly repeated surveys to explore the interactive and lag effects of environmental factors on snail density and to monitor their long-term and seasonal trends in a bottomland around the Dongting Lake region in China. Relevant environmental data were obtained from multiple sources. A Bayesian kernel machine regression model and a Bayesian temporal model combined with a distributed lag model were constructed to analyze interactive and lag effects of environmental factors on snail density. The results indicated the average annual snail density in the study site exhibited an increasing and then decreasing trend, peaking in 2013. Snail densities were the highest in October and the lowest in January in a year. Normalized Difference Vegetation Index (NDVI) and water level were the most effective predictors of snail density, with potential interactions among temperature, precipitation, and NDVI. The mean minimum temperature in January, water level, precipitation and NDVI were positively correlated with snail density at lags ranging from 1 to 4 months. These findings could serve as references for relevant authorities to monitor the changing trend of snail density and implement control measures, thereby reducing the occurrence of schistosomiasis.

Schistosomiasis, a prevalent public health issue specifically in sub-Saharan Africa, is primarily attributed to Schistosoma haematobium and Schistosoma mansoni , often occurring concurrently. These schistosome species share similarities in life cycles and transmission, manifesting comparable infection patterns and susceptibility to temperature variations. This study investigates the influence of temperature control not only on the transmission of individual species but also on their mutual interactions and co-infection dynamics using a mathematical model. Sub-models and co-dynamic properties, including reproduction numbers, equilibrium states, and stability conditions, are derived. Sensitivity analysis is performed to clarify the impact of parameter variations on model stability. Results suggest that temperature variation increases the spread of S. haematobium , which enhances susceptibility to S. mansoni co-infection, possibly by altering the immune response. At moderate temperatures (20°C and 25°C), infection levels in both single and co-infected individuals are higher, while recovery rates increase with temperature, peaking at 25°C and 35°C as infections significantly decrease. Biomphalaria snails exhibit greater population growth and susceptibility to infection than Bulinus snails, particularly below 25°C. Above this temperature, Biomphalaria population decreases while Bulinus species are more likely to experience faster mortality. These temperature-related variations differently impact mortality rates of intermediate snails and snail-to-human transmissibility rates for schistosome species, holding significant health implications. Targeting snails during seasons below 25°C, when susceptibility is higher, and intensifying human treatment interventions around 25°C–35°C, where recovery rates peak, may yield optimal results, particularly during seasons with intermediate temperatures around 25°C for both snails and humans. The results underscore the importance of integrating temperature into models for predicting and managing schistosomiasis dynamics for both genera. Therefore, this model is applicable not only to sub-Saharan Africa, but also to other regions where the described temperature ranges match with the local climate.

Human schistosomiasis is a parasitic disease caused by an infection with trematodes of the genus The disease mainly affects impoverished populations. Around 800 million people are exposed to the infection, which is a public health problem in the tropical and subtropical regions of Africa, Asia, the Caribbean and South America. In Brazil, is the only species that causes schistosomiasis and the disease is widely distributed. Conventional diagnosis of the disease is carried out by detecting eggs using parasitological methods, such as the Kato-Katz test. Schistosomiasis has been reported in all regions of Brazil and is characterized as endemic in seven states in the Northeast Region and two states in the Southeast Region. In 2015, 78,7% of all cases reported in Brazil occurred in the Northeast Region. It is estimated that 1,5 million people is infected with this disease in Brazil and more than 25 millions live in areas with a high risk of transmission. Despite the reduction in mortality and morbidity, schistosomiasis was responsible for 8,756 deaths between 2000 and 2011 and 2,517 deaths between 2015 and 2019 in Brazil and it remains an important public health problem. In the state of Rio de Janeiro, some areas have low endemicity or isolated foci of and the majority of infected individuals have mild infections. The last survey of the disease in the state of Rio de Janeiro was carried out between 2010 and 2015 in students aged 7 to 17.Schistosomiasis was reported in 10 of the 21 municipalities studied. Of the 5,111 school children screened for infection, 46 (1,65%) were tested positive. Studies carried out in areas of low endemicity in Rio de Janeiro showed that among the 205 patients infected by in Sumidouro, around 84% were aged 14 or over and all, except one individual, had the intestinal form (91,2%) or hepato-intestinal (8,3%) of schistosomiasis. Another study carried out in Sumidouro showed that with tests based on patent egg infection determined by the Kato-Katz test, active infections were diagnosed in eight (8/108) individuals. The intensity of infection expressed by parasite loads ranged from 6 to 72 eggs per gram of feces/individual. The results showed DNA amplification in 32 of the 100 individuals tested by real-time PCR. All individuals with patent ovo infection showed positive DNA amplification. These studies showed that if we only analyzed school-age children using the Kato-Katz test, the majority of the infected population would never be diagnosed with infection. In situations of low endemicity, with low intensities of infection, with low severity in the population and in the most affected age groups, schistosomiasis requires a more sensitive diagnostic approach (e.g. screening by PCR rather than Kato test), otherwise many infected individuals will remain invisible to the healthcare system.

Biomphalaria snails are instrumental in transmission of the human blood fluke Schistosoma mansoni . With the World Health Organization's goal to eliminate schistosomiasis as a global health problem by 2025, there is now renewed emphasis on snail control. Here, we characterize the genome of Biomphalaria glabrata, a lophotrochozoan protostome, and provide timely and important information on snail biology. We describe aspects of phero-perception, stress responses, immune function and regulation of gene expression that support the persistence of B . glabrata in the field and may define this species as a suitable snail host for S . mansoni . We identify several potential targets for developing novel control measures aimed at reducing snail-mediated transmission of schistosomiasis. B iomphalaria glabrata  is a fresh water snail that acts as a host for trematode  Schistosoma mansoni  that causes intestinal infection in human. This work describes the genome and transcriptome analyses from 12 different tissues of  B glabrata , and identify genes for snail behavior and evolution.

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.

Programs for schistosomiasis control are advancing worldwide, with many benefits noted in terms of disease reduction. Yet risk of reinfection and recurrent disease remain, even in areas with high treatment coverage. In the search for means to better prevent new Schistosoma infections, attention has returned to an older strategy for transmission control, i.e., chemical mollusciciding, to suppress intermediate host snail species responsible for S. mansoni and S. haematobium transmission. The objective of this systematic review and meta-analysis was to summarize prior experience in molluscicide-based control of Bulinus and Biomphalaria spp. snails, and estimate its impact on local human Schistosoma infection. The review was registered at inception with PROSPERO (CRD42013006869). Studies were identified by online database searches and hand searches of private archives. Eligible studies included published or unpublished mollusciciding field trials performed before January 2014 involving host snails for S. mansoni or S. haematobium, with a primary focus on the use of niclosamide. Among 63 included papers, there was large variability in terms of molluscicide dosing, and treatment intervals varied from 3-52 weeks depending on location, water source, and type of application. Among 35 studies reporting on prevalence, random effects meta-analysis indicated that, on average, odds of infection were reduced 77% (OR 0.23, CI95% 0.17, 0.31) during the course of mollusciciding, with increased impact if combined with drug therapy, and progressively greater impact over time. In 17 studies reporting local incidence, risk of new infection was reduced 64% (RR 0.36 CI95% 0.25, 0.5), but additional drug treatment did not appear to influence incidence effects. While there are hurdles to implementing molluscicide control, its impact on local transmission is typically strong, albeit incomplete. Based on past experience, regular focal mollusciciding is likely to contribute significantly to the move toward elimination of schistosomiasis in high risk areas.

Background Relating the geographical distribution of intermediate freshwater snail hosts (viz. vectors of schistosomes) to local environmental attributes offers value for understanding the epidemiological landscape of schistosomiasis transmission in a changing aquatic environment. Schistosomiasis—both urogenital and intestinal—causes significant human suffering, affecting approximately 240 million people globally and grouped within the neglected tropical disease (NTD) umbrella. This study addresses the following questions: 1. Where are the most suitable habitats for intermediate host snails in the Lower Shire Valley (LSV) in Malawi? 2. Which environmental factors are strongly associated with the geographical distribution of such snails in the LSV? Methods This paper presents the first species distribution models (SDMs) for intermediate snail hosts for urogenital and intestinal schistosomiasis in Chikwawa and Nsanje Districts, which together form the LSV). The SDMs developed for this study are ensemble machine learning approaches based on Random Forest (RF), Support Vector Machines (SVM), and multilayer perceptron (MLP) and are specific to the Bulinus africanus group and Biomphalaria pfeifferi . The former transmits urogenital schistosomiasis ( Schistosoma haematobium ), while the latter transmits intestinal schistosomiasis ( Schistosoma mansoni ). Results The SDMs reveal the following: 1) currently, Bu. africanus group not only has a wide distribution across central Chikwawa and eastern Nsanje but is also concentrated in floodplains, and the LSV has few habitats that can support Bi. pfeifferi , and 2) vegetation cover is the most important predictor of Bu. africanus group distribution, whereas precipitation variables are most important for Bi. pfeifferi in the LSV. Thus, Bu. africanus group habitat is the most dominant and abundant, while Bi. pfeifferi suitable habitat is patchy and scarce. Conclusion The distribution of suitable habitats for potential urogenital and intestinal schistosomiasis transmission across LSV is not uniform and typically non-overlapping. Understanding the spatial and temporal distributions of these snails is important for controlling and eliminating schistosomiasis. Graphical Abstract

Schistosomiasis is a neglected tropical disease caused by infection with blood flukes of the genus Schistosoma. Widely distributed in the Middle East, southeast Asia, Latin America, and (mostly) sub-Saharan Africa, schistosomiasis is acquired upon skin penetration of infective larvae released by freshwater snails. Acute infection might present with self-limiting hypersensitivity reactions (known as Katayama fever). Chronic infection typically leads to two main clinical patterns: intestinal or urogenital schistosomiasis, depending on the infecting species. Impairment of other body sites (eg, the CNS or respiratory tract) can occur. The intestinal form is characterised by abdominal pain and diarrhoea, with or without blood; complications are hepatic fibrosis, portal hypertension, splenomegaly, and variceal bleeding. The urogenital form is characterised by dysuria and haematuria; complications are renal failure and squamous-cell carcinoma of the bladder. Conventional diagnosis is based on egg detection in faeces or urine, although sensitivity might be low. Praziquantel is the first-line treatment, and it is also provided in preventive chemotherapy campaigns by mass drug administration to afflicted communities.

While the dispersal of hosts and vectors-through active or passive movement-is known to facilitate the spread and re-emergence of certain infectious diseases, little is known about the movement ecology of Oncomelania spp., intermediate snail host of the parasite Schistosoma japonicum, and its consequences for the spread of schistosomiasis in East and Southeast Asia. In China, despite intense control programs aimed at preventing schistosomiasis transmission, there is evidence in recent years of re-emergence and persistence of infection in some areas, as well as an increase in the spatial extent of the snail host. A quantitative understanding of the dispersal characteristics of the intermediate host can provide new insights into the spatial dynamics of transmission, and can assist public health officials in limiting the geographic spread of infection. Oncomelania hupensis robertsoni snails (n = 833) were sampled from 29 sites in Sichuan, China, genotyped, and analyzed using Bayesian assignment to estimate the rate of recent snail migration across sites. Landscape connectivity between each site pair was estimated using the geographic distance distributions derived from nine environmental models: Euclidean, topography, incline, wetness, land use, watershed, stream use, streams and channels, and stream velocity. Among sites, 14.4% to 32.8% of sampled snails were identified as recent migrants, with 20 sites comprising >20% migrants. Migration rates were generally low between sites, but at 8 sites, over 10% of the overall host population originated from one proximal site. Greater landscape connectivity was significantly associated with increased odds of migration, with the minimum path distance (as opposed to median or first quartile) emerging as the strongest predictor across all environmental models. Models accounting for land use explained the largest proportion of the variance in migration rates between sites. A greater number of irrigation channels leading into a site was associated with an increase in the site's propensity to both attract and retain snails. Our findings have important implications for controlling the geographic spread of schistosomiasis in China, through improved understanding of the dispersal capacity of the parasite's intermediate host.