Cryptic population structure and transmission dynamics uncovered for Schistosoma mansoni populations by genetic analyses.

Patterns of diversity in pathogen genomes provide a window into the spatiotemporal spread of disease. In this study, we tested the hypothesis that Schistosoma mansoni parasites form genetic clusters that coincide with the communities of their human hosts. We also looked for genetic clustering of parasites at the sub-community level. Our data consists of 14 microsatellite DNA markers, typed from pooled DNA samples from [Formula: see text] infected individuals living in three Brazilian communities. We found a one-to-one correspondence between genetic clusters found by K-means cluster analysis and communities when [Formula: see text]. These clusters are also easily identified in a neighbor-joining tree and principal coordinates plots. K-means analysis with [Formula: see text] also reveals genetic clusters of parasites at the sub-community level. These sub-clusters also appear on the neighbor-joining tree and principal coordinates plots. A surprising finding is a genetic relationship between subgroups in widely separated human communities. This connection suggests the existence of common transmission sites that have wide influence. In summary, the genetic structure of S. mansoni in Brazil juxtaposes local isolation that is occasionally broken by long-range migration. Permanent eradication of schistosomes will require both local efforts and the identification of regional infection reservoirs.

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.

Comparative Vectorial Competence of Biomphalaria sudanica and Biomphalaria choanomphala, Snail Hosts of Schistosoma mansoni, From Transmission Hotspots In Lake Victoria, Western Kenya.

Schistosoma mansoni, which causes human intestinal schistosomiasis, continues to be a major public health concern in the Lake Victoria basin in western Kenya, with Biomphalaria sudanica (a shoreline inhabiting snail) and Biomphalaria choanomphala (a deep-water snail) playing roles in transmission. A recent study showed that B. sudanica was abundantly present near all study villages on the lakeshore, but B. choanomphala was significantly more abundant near villages known to be persistent transmission hotspots. The present study investigated the relative compatibility of B. sudanica and B. choanomphala with S. mansoni. A reciprocal cross-infection experiment used young adult F1 generation B. sudanica and B. choanomphala that were exposed to either 1, 5, or 10 sympatric or allopatric human-derived S. mansoni miracidia. Three weeks post-exposure (PE) and weekly thereafter, the snails were counted and screened for schistosome cercariae, and at 7 wk PE, total cercariae shed during a 2 hr period by each infected snail was determined. Pre-patent periods for S. mansoni in both B. sudanica and B. choanomphala were similar, and most snails in all exposure combinations started shedding cercariae 5 wk PE. Prevalences were significantly higher in B. choanomphala (12.2-80.9%) than in B. sudanica (5.2-18.6%) at each dose, regardless of whether miracidia were of an allopatric or a sympatric source (P < 0.0001). Overall, the odds of a snail becoming infected with 5 or 10 miracidia were significantly higher than the odds of being infected with 1 miracidium, (P < 0.0001), and fewer cercariae were produced by snails exposed to single as compared to 5 or 10 miracidia. On average, B. choanomphala produced more cercariae ( = 458, SD = 414) than B. sudanica ( = 238, SD = 208) (P < 0.0001). These results suggest that B. choanomphala is more compatible with S. mansoni than B. sudanica. Though B. choanomphala can be found in shallow shoreline waters, it is, for the most part, a deeper-water taxon. Because dredging is a relatively inefficient means of sampling, B. choanomphala is likely underestimated with respect to its population size, the number of S. mansoni-positive snails, and its role in maintaining transmission.

Interventions can shift the thermal optimum for parasitic disease transmission.

Temperature constrains the transmission of many pathogens. Interventions that target temperature-sensitive life stages, such as vector control measures that kill intermediate hosts, could shift the thermal optimum of transmission, thereby altering seasonal disease dynamics and rendering interventions less effective at certain times of the year and with global climate change. To test these hypotheses, we integrated an epidemiological model of schistosomiasis with empirically determined temperature-dependent traits of the human parasite Schistosoma mansoni and its intermediate snail host (Biomphalaria spp.). We show that transmission risk peaks at 21.7 °C (Topt ), and simulated interventions targeting snails and free-living parasite larvae increased Topt by up to 1.3 °C because intervention-related mortality overrode thermal constraints on transmission. This Topt shift suggests that snail control is more effective at lower temperatures, and global climate change will increase schistosomiasis risk in regions that move closer to Topt Considering regional transmission phenologies and timing of interventions when local conditions approach Topt will maximize human health outcomes.

Schistosomiasis Morbidity Hotspots: Roles of the Human Host, the Parasite and Their Interface in the Development of Severe Morbidity.

Schistosomiasis is the second most important human parasitic disease in terms of socioeconomic impact, causing great morbidity and mortality, predominantly across the African continent. For intestinal schistosomiasis, severe morbidity manifests as periportal fibrosis (PPF) in which large tracts of macro-fibrosis of the liver, visible by ultrasound, can occlude the main portal vein leading to portal hypertension (PHT), sequelae such as ascites and collateral vasculature, and ultimately fatalities. For urogenital schistosomiasis, severe morbidity manifests as pathology throughout the urinary system and genitals, and is a definitive cause of squamous cell bladder carcinoma. Preventative chemotherapy (PC) programmes, delivered through mass drug administration (MDA) of praziquantel (PZQ), have been at the forefront of schistosomiasis control programmes in sub-Saharan Africa since their commencement in Uganda in 2003. However, despite many successes, 'biological hotspots' (as distinct from 'operational hotspots') of both persistent high transmission and morbidity remain. In some areas, this failure to gain control of schistosomiasis has devastating consequences, with not only persistently high infection intensities, but both "subtle" and severe morbidity remaining prevalent. These hotspots highlight the requirement to revisit research into severe morbidity and its mechanisms, a topic that has been out of favor during times of PC implementation. Indeed, the focality and spatially-structured epidemiology of schistosomiasis, its transmission persistence and the morbidity induced, has long suggested that gene-environmental-interactions playing out at the host-parasite interface are crucial. Here we review evidence of potential unique parasite factors, host factors, and their gene-environmental interactions in terms of explaining differential morbidity profiles in the human host. We then take the situation of schistosomiasis mansoni within the Albertine region of Uganda as a case study in terms of elucidating the factors behind the severe morbidity observed and the avenues and directions for future research currently underway within a new research and clinical trial programme (FibroScHot).

Factors Associated with Schistosoma mansoni Infestation in Northeast Brazil: A Need to Revisit Individual and Community Risk Factors.

In Brazil, schistosomiasis continues to be an important health issue. The aim of this study was to identify factors associated with Schistosoma mansoni infestation. A cross-sectional study was performed to assess factors associated with S. mansoni endemicity in a municipality in Northeast Brazil with a history of reporting schistosomiasis. Participants were divided into four groups: 1) new S. mansoni cases (n = 44), 2) past history of S. mansoni treatment (n = 78), 3) immediate neighbors (n = 158), and 4) nearby controls (n = 35). Multiple comparisons analysis was performed. Subjects had a mean of 6.6 ± 3.9 years of education, and no difference was observed regarding family income (one-way analysis of variance, P = 0.215). A total of 95.9% of the individuals had rudimentary cesspit as sanitary wastewater. The mean body mass index was 28.3 ± 5.1, with 41.0% and 24.1% overweight and obesity, respectively. Of note, 28.9% of adults had hypertension. Hemoglobin, mean corpuscular volume, and mean corpuscular hemoglobin were higher in the recent S. mansoni treated group (Wilks' lambda, P < 0.001). Male gender was more prevalent in new S. mansoni cases (likelihood ratio, P < 0.001), close proximity to water collections was a risk for S. mansoni infestation (likelihood ratio, P < 0.001), and a better hematological status was observed in individuals recently treated with praziquantel. This study indicates the need to maintain surveillance for S. mansoni in low-transmission areas and the need to establish community-based interventions to control transmission.

Schistosoma mansoni Eggs Modulate the Timing of Granuloma Formation to Promote Transmission.

Schistosome eggs provoke the formation of granulomas, organized immune aggregates, around them. For the host, the granulomatous response can be both protective and pathological. Granulomas are also postulated to facilitate egg extrusion through the gut lumen, a necessary step for parasite transmission. We used zebrafish larvae to visualize the granulomatous response to Schistosomamansoni eggs and inert egg-sized beads. Mature eggs rapidly recruit macrophages, which form granulomas within days. Beads also induce granulomas rapidly, through a foreign body response. Strikingly, immature eggs do not recruit macrophages, revealing that the eggshell is immunologically inert. Our findings suggest that the eggshell inhibits foreign body granuloma formation long enough for the miracidium to mature. Then parasite antigens secreted through the eggshell trigger granulomas that facilitate egg extrusion into the environment. In support of this model, we find that only mature S. mansoni eggs are shed into the feces of mice and humans.

New epidemiological profile of schistosomiasis from an area of low prevalence in Brazil.

INTRODUCTION: Schistosomiasis, caused by infection from Schistosoma mansoni, is a disease that represents an important public health problem for Brazil, especially for states in the Northeast region. Thus, the aim of this study is to present a new epidemiological profile for the disease in a municipality with low prevalence in the state of Alagoas, Brazil. METHODS: A cross-sectional study was conducted through a coproparasitological and malacological survey. A structured questionnaire was applied to the study participants to survey possible risk factors and a spatial analysis (kernel density) was used to measure the risk of infection. RESULTS: Of the 347 participants, 106 (30.5%) were infected by Schistosoma mansoni, most of them from the urban area of the municipality (68.9%; 73/106). A 3-fold risk of infection was found for individuals living in the urban area and a risk of 2.15 times for self-declared farmers. Biomphalaria glabrata and B. straminea were the species found in the municipality, but no animals were diagnosed as infected by the parasite. Spatial analysis showed a random distribution of vectors and human cases of the disease, and the formation of two clusters of human cases in the urban area was seen. CONCLUSIONS: A new epidemiological profile for schistosomiasis from S. mansoni infection was presented in a municipality of low endemicity: a high proportion of positive individuals in the urban area; presence of snails without positive diagnosis for S. mansoni infection; random distribution of vectors and human cases; and absence of association between classical risk factors and human infection.

Comparing PCR techniques against conventional cercarial shedding methods for detecting Schistosoma mansoni infection in Biomphalaria snails.

The detection of Schistosoma mansoni infection in both its intermediate (snail) and definitive (human) hosts is useful in providing information on the transmission of schistosomiasis. Three pairs of previously designed PCR primers (SM1-7, SMF/R & ND5) used for the detection of S. mansoni infection were tested. We assess the utility of each of these primer sets for detecting S. mansoni infection both in artificially exposed laboratory bred Biomphalaria glabrata, and field infected African Biomphalaria sudanica and Biomphalaria pfeifferi. Two of the three primer sets (SMF/R & ND5) detected S. mansoni infection in snails, but amplification of S. mansoni DNA with SM1-7 was unreliable. For the artificially exposed laboratory bred B. glabrata snails, SMF/R and ND5 both detected infection in more snails than the cercarial shedding method. Infection detection rates were 62.4% for ND5, 57.1% for SMF/R and 50.4% using traditional cercarial shedding methods. Both SMF/R and ND5 detected S. mansoni infection in 91% of snails observed shedding cercariae, increasing to 98.5% when low stringency PCR methods were used. When comparing each of the detection methods using a Bayesian latent class analysis model, ND5 had the highest detection sensitivity and negative predictive value (NPV), while SMF/R had the highest detection specificity and positive predictive value (PPV). In field collected Biomphalaria snails, ND5 detected S. mansoni infection in 21 of 24 snails categorised as shedding S. mansoni cercariae and 4 of 24 snails categorised as shedding non-S. mansoni cercariae, while SMF/R detected infection in 18 of 24 snails categorised as shedding S. mansoni cercariae and in 3 of 24 snails categorised as shedding non-S. mansoni cercariae. All SMF/R and ND5 PCR products were shown to be S. mansoni indicating that these field snails must have been infected with both S. mansoni and cercariae from other Schistosoma species. This indicates that the two primer sets are specific for S. mansoni and will not amplify non-S. mansoni species when used at their recommended annealing temperatures. Both the SMF/R and ND5 primers effectively detected S. mansoni infection in three Biomphalaria species and have improved detection sensitivity over cercarial shedding.

Schistosoma mansoni Vector Snails in Antigua and Montserrat, with Snail-Related Considerations Pertinent to a Declaration of Elimination of Human Schistosomiasis.

Investigations leading to a WHO-validated declaration of elimination of schistosomiasis transmission are contemplated for several countries, including Caribbean island nations. With assistance from the Pan American Health Organization, we undertook freshwater snail surveys in two such nations, Antigua and Barbuda, and Montserrat in September and October 2017. Historically, the transmission of Schistosoma mansoni supported by the Neotropical vector snail Biomphalaria glabrata occurred in both countries. Transmission on the islands is thought to have been interrupted by the treatment of infected people, improved sanitation, introduction of competitor snails, and on Montserrat with the eruption of the Soufrière volcano which decimated known B. glabrata habitats. Guided by the available literature and local expertise, we found Biomphalaria snails in seven of 15 and one of 14 localities on Antigua and Montserrat, respectively, most of which were identified anatomically and molecularly as Biomphalaria kuhniana. Two localities on Antigua harbored B. glabrata, but no schistosome infections in snails were found. For snail-related aspects of validation of elimination, there are needs to undertake basic local training in medical malacology, be guided by historical literature and recent human schistosomiasis surveys, improve and validate sampling protocols for aquatic habitats, enlist local expertise to efficiently find potential transmission sites, use both anatomical and molecular identifications of schistosomes or putative vector snail species found, if possible determine the susceptibility of recovered Biomphalaria spp. to S. mansoni, publish survey results, and provide museum vouchers of collected snails and parasites as part of the historical record.

Characteristics of persistent hotspots of Schistosoma mansoni in western Côte d'Ivoire.

BACKGROUND: Preventive chemotherapy with praziquantel is the cornerstone of schistosomiasis control. However, in some social-ecological settings, the prevalence and/or intensity of Schistosoma infection does not lower meaningfully despite multiple rounds of preventive chemotherapy, a phenomenon termed persistent hotspot (PHS). We assessed the characteristics of PHS in a Schistosoma mansoni-endemic area of Côte d'Ivoire. METHODS: In October 2016, a cross-sectional survey was conducted in 14 schools in the western part of Côte d'Ivoire, one year after multiple rounds of preventive chemotherapy. In each school, 50 children aged 9-12 years provided two stool samples and one urine sample. Stool samples were subjected to triplicate Kato-Katz thick smears for S. mansoni diagnosis. Urine samples were examined by a filtration method for S. haematobium eggs. PHS was defined as failure to achieve a reduction in the prevalence of S. mansoni infection of at least 35% and/or a reduction of infection intensity of at least 50%. Six schools underwent more detailed investigations, including a questionnaire survey for demographic characteristics and a malacological survey. RESULTS: In the six schools subjected to detailed investigations, the overall prevalence of S. mansoni and S. haematobium was 9.5% and 2.6%, respectively. Four schools were classified as PHS. The S. mansoni prevalence in the four PHS was 10.9% compared to 6.6% in the remaining two schools. The S. mansoni infection intensity, expressed as arithmetic mean eggs per gram of stool (EPG) among infected children, was 123.8 EPG in PHS and 18.7 EPG in the other two schools. Children bathing in open freshwater bodies were at higher odds of S. mansoni infection (odds ratio: 4.5, 95% confidence interval: 1.6-12.6). A total of 76 human-water contact sites (53 in PHS and 23 in the other schools) were examined and 688 snails were collected, including potential intermediate host snails of Schistosoma (Biomphalaria pfeifferi, Bulinus forskalii, Bu. globosus and Bu. truncatus). CONCLUSION: Children in PHS schools bathed more frequently in open freshwater bodies, and hence, they are more exposed to Schistosoma transmission. Our findings call for an integrated control approach, complementing preventive chemotherapy with other interventions, particularly in PHS settings.

Schistosomiasis Control in Nigeria: Moving Round the Circle?

Background: Schistosomiasis has continued to plague low-resource areas of the Nigerian population. Mass drug administration (MDA) has been the only adopted interventional program for decades. However, it appears this effort does not culminate in transmission and morbidity reduction. Purpose: To highlight the current situation of schistosomiasis in Nigeria, why MDA alone cannot achieve the expected result, identify research needs, and promotion of integrated control approach for schistosomiasis. Method: A viewpoint based on practices, research findings, and personal and professional experience in the field of schistosomiasis control. Conclusion: This viewpoint strongly advocates a commitment to the integrated control approach through the development of robust schistosomiasis control policy for the country. It stressed the need for research priorities in neglected areas of schistosomiasis that are germane for control of the disease. The government's willpower to implement important recommendations from research outcomes is important to achieve success.

The potential risk of Schistosoma mansoni transmission by the invasive freshwater snail Biomphalaria straminea in South China.

Schistosomes infect more than 200 million people worldwide, and globally, over 700 million people are at risk of infection. The snail Biomphalaria straminea, as one of the intermediate hosts of Schistosoma mansoni, consecutively invaded Hong Kong in 1973, raising great concern in China. In this study, a malacological survey was conducted over a period of four years, and investigations were performed on the mechanism of susceptibility of B. straminea to S. mansoni. B. straminea was investigated in China from 2014 to 2018. Out of 185 investigated sites, 61 were positive for stages of black B. straminea (BBS), which shows pigmented spots. Twenty of the 61 sites were positive for red B. straminea (RBS), which is partially albino and red colored. Phylogenetic analyses based on cox1 and 18S rRNA sequences demonstrated that both phenotypes were clustered with Brazilian strains. No S. mansoni infections were detected in field-collected snail. However, in laboratory experiments, 4.17% of RBS were susceptible to a Puerto Rican strain of S. mansoni, while BBS was not susceptible. The highest susceptibility rate (70.83%) was observed in the F2 generation of RBS in lab. The density of RBS has increased from south to north and from west to east in Guangdong since 2014. Five tyrosinase tyrosine metabolism genes were upregulated in BBS. Transcriptome comparisons of RBS and BBS showed that ficolin, C1q, MASP-like, and membrane attack complex (MAC)/perforin models of the complement system were significantly upregulated in BBS. Our study demonstrated that B. straminea is widely distributed in Hong Kong and Guangdong Province, which is expanding northwards very rapidly as a consequence of its adaptation to local environments. Our results suggest that B. straminea from South China is susceptible to S. mansoni, implying the high potential for S. mansoni transmission and increased S. mansoni infection risk in China.

Genetic diversity of Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni in Shamva district, Zimbabwe: role on intestinal schistosomiasis transmission.

The fresh water snail Biomphalaria pfeifferi is the intermediate host for Schistosoma mansoni, which causes human intestinal schistosomiasis in Zimbabwe. Despite the medical importance of this intermediate host, there are no current data on its molecular characterization in Zimbabwe. In 2016, human water contact sites were identified in four communities in Madziwa area, Shamva district, Zimbabwe. The survey sites were recorded and mapped using a global positioning system. A 655 bp region of the mitochondrial cytochrome oxidase subunit I gene was amplified in 70 B. pfeifferi snails. The sequence data were analysed to determine the relationships between the individual snails, their inter, intra population diversity and structure. Overall, four unique cox1 haplotypes, with a haplotype diversity of 0.608, were identified in the snails. One haplotype spanned across most of the sites. There was no clear geographical clustering of haplotypes. The mean diversity among the haplotypes was very low (0.009), while the net divergence among the collection sites ranged from 0.000 to 0.026. The diversity within and between the sites was 0.017 and 0.012 respectively. This data advances our knowledge of the understanding of the population structure of B. pfeifferi in Madziwa area, Zimbabwe, with the high occurrence of one haplotype indicating the possibility of a recent bottleneck followed by population expansion. The population genetic structure of B. pfeifferi snails described here has provided an opportunity to investigate the contribution of snail genetics to variation in disease burden; and development of control strategies that exploit genetic differences in susceptibility to parasites.

Identification of transmission foci of Schistosoma mansoni: narrowing the intervention target from district to transmission focus in Ethiopia.

BACKGROUND: Schistosoma mansoni (S. mansoni) infection is a significant public health problem in Ethiopia, and has wide distribution in the country. The impact of the disease is particularly high on school-age children. Nationwide 385 endemic districts were identified, whereby control and elimination interventions are underway using school-based annual mass drug administration (MDA) with praziquantel. The national elimination program targets endemic districts as a whole. The aim of this study was to identify the transmission foci of Schistosoma mansoni and determine prevalence of soil-transmitted helminths (STHs) in Abeshge district. METHODS: The study was conducted from April to May, 2019 among school-age children randomly selected from public elementary schools in Abeshge district, South-central Ethiopia. Demographic information and data on risk factors of S. mansoni infection were gathered using pre-tested questionnaire. Moreover, a stool sample was collected from each child and examined using Kato-Katz thick smear technique. The data were analyzed using STATA_MP version 12. RESULTS: A total of 389 school-age children from five public elementary schools were included in the study. The overall prevalence of S. mansoni and STHs was 19.3% (75/389) and 35% (136/389), respectively. The prevalence of S. mansoni was 60.6% in Kulit Elementary school, while it was zero in Geraba. The prevalence of S. mansoni was significantly higher among males (AOR = 2.6, 95% CI 1.3-5.1), those with habit of swimming and/or bathing in rivers (AOR = 2.9, 95%CI 1.3-5.1) and involved in irrigation activities (AOR = 2.9, 95% CI 1.0-8.3). Overall, the prevalence of S. mansoni was significantly higher among school children attending Kulit Elementary School compared to those attending the remaining schools (AOR = 12.5, 95%CI 6.2-25.1). CONCLUSION: A wide variation of S. mansoni prevalence was observed among the school children in the different schools. Control interventions better identify and target foci of S. mansoni transmission, instead of targeting the district homogenously.

Impact of Different Mass Drug Administration Strategies for Gaining and Sustaining Control of Schistosoma mansoni and Schistosoma haematobium Infection in Africa.

This report summarizes the design and outcomes of randomized controlled operational research trials performed by the Bill & Melinda Gates Foundation-funded Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) from 2009 to 2019. Their goal was to define the effectiveness and test the limitations of current WHO-recommended schistosomiasis control protocols by performing large-scale pragmatic trials to compare the impact of different schedules and coverage regimens of praziquantel mass drug administration (MDA). Although there were limitations to study designs and performance, analysis of their primary outcomes confirmed that all tested regimens of praziquantel MDA significantly reduced local Schistosoma infection prevalence and intensity among school-age children. Secondary analysis suggested that outcomes in locations receiving four annual rounds of MDA were better than those in communities that had treatment holiday years, in which no praziquantel MDA was given. Statistical significance of differences was obscured by a wider-than-expected variation in community-level responses to MDA, defining a persistent hot spot obstacle to MDA success. No MDA schedule led to elimination of infection, even in those communities that started at low prevalence of infection, and it is likely that programs aiming for elimination of transmission will need to add supplemental interventions (e.g., snail control, improvement in water, sanitation and hygiene, and behavior change interventions) to achieve that next stage of control. Recommendations for future implementation research, including exploration of the value of earlier program impact assessment combined with intensification of intervention in hot spot locations, are discussed.

Application of Schistosomiasis Consortium for Operational Research and Evaluation Study Findings to Refine Predictive Modeling of Schistosoma mansoni and Schistosoma haematobium Control in Sub-Saharan Africa.

An essential mission of the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) was to help inform global health practices related to the control and elimination of schistosomiasis. To provide more accurate, evidence-based projections of the most likely impact of different control interventions, whether implemented alone or in combination, SCORE supported mathematical modeling teams to provide simulations of community-level Schistosoma infection outcomes in the setting of real or hypothetical programs implementing multiyear mass drug administration (MDA) for parasite control. These models were calibrated using SCORE experience with Schistosoma mansoni and Schistosoma haematobium gaining and sustaining control studies, and with data from comparable programs that used community-based or school-based praziquantel MDA in other parts of sub-Saharan Africa. From 2010 to 2019, models were developed and refined, first to project the likely SCORE control outcomes, and later to more accurately reflect impact of MDA across different transmission settings, including the role of snail ecology and the impact of seasonal rainfall on snail abundance. Starting in 2014, SCORE modeling projections were also compared with the models of colleagues in the Neglected Tropical Diseases Modelling Consortium. To explore further possible improvement to program-based control, later simulations examined the cost-effectiveness of combining MDA with environmental snail control, and the utility of early impact assessment to more quickly identify persistent hot spots of transmission. This article provides a nontechnical summary of the 11 SCORE-related modeling projects and provides links to the original open-access articles describing model development and projections relevant to schistosomiasis control policy.

Soil-transmitted helminths and schistosomiasis among pre-school age children in a rural setting of Busia County, Western Kenya: a cross-sectional study of prevalence, and associated exposures.

BACKGROUND: Soil-transmitted helminths (STH) and schistosomiasis continue to cause serious health problems among affected communities. To ensure that infection transmission levels are reduced, repeated mass drug administration at regular intervals has been recommended by World Health Organization. Pre-school age children (PSAC) have been neglected both in terms of research activities and in control programmes in the past for reasons that they carry insignificant infection levels. The current study determined risk factors that contribute to differences in infection prevalence among enrolled and non-enrolled PSAC in Busia County, western Kenya. METHODS: This was a comparative cross-sectional study that compared STH and Schistosoma mansoni infections among enrolled and non-enrolled PSAC in Busia County. Simple random sampling was used to select study participants. A total of 327 enrolled and 326 non-enrolled PSAC (n = 653) were recruited from five participating schools, and the neighboring villages. Statistical analysis was performed using STATA version 14 (STATA Corporation, College Station, TX, USA). Differences in proportions were assessed using the z-test statistic for testing sample proportions. Univariable and multivariable logistic regression were used to test the associations between the variables. RESULTS: The prevalence of STH and Schistosoma mansoni infection was 17.0% (95%CI: 13.1-22.1), and 11.8% (95%CI:11.0-12.9) respectively. Specific STH species prevalence were 12.9% (95%CI:7.0-23.5) for Trichuris trichiura, 8.3% (95%CI:8.2-8.3) for Ascaris lumbricoides, and 1.2% (95%CI:1.2-1.2) for hookworms. Prevalence of T. trichiura was higher among enrolled PSAC 16.9% (95%CI: 6.8-41.9); p = 0.003, compared to the non-enrolled 8.9% (95%CI:4.3-18.2). From univariable analysis, lack of improved water source for drinking OR 2.01, (95%CI:1.29-3.13); p = 0.002, and not wearing shoes OR 3.42, (95%CI:1.14-10.29); p = 0.028, were some of the significant factors associated with STH infection. While for multivariable analysis, bathing/swimming in a river daily, aOR 3.99 (95%CI:1.98-8.06); p = 0.001 was a key significant factor for S. mansoni infections. CONCLUSION: There was high prevalence of STH infection among enrolled PSAC despite having participated in the national school-based deworming programme. Hence the need for continued mass drug administration to reduce the intensity of infections among these age group. In addition, further research maybe needed to identify drivers of STH infection particularly T. trichiura among PSAC.

Effects of temperature and viscosity on miracidial and cercarial movement of Schistosoma mansoni: ramifications for disease transmission.

Parasites with complex life cycles can be susceptible to temperature shifts associated with seasonal changes, especially as free-living larvae that depend on a fixed energy reserve to survive outside the host. The life cycle of Schistosoma, a trematode genus containing some species that cause human schistosomiasis, has free-living, aquatic miracidial and cercarial larval stages that swim using cilia or a forked tail, respectively. The small size of these swimmers (150-350 µm) dictates that their propulsion is dominated by viscous forces. Given that viscosity inhibits the swimming ability of small organisms and is inversely correlated with temperature, changes in temperature should affect the ability of free-living larval stages to swim and locate a host. By recording miracidial and cercarial movement of Schistosoma mansoni using a high-speed camera and manipulating temperature and viscosity independently, we assessed the role each factor plays in the swimming mechanics of the parasite. We found a positive effect of temperature and a negative effect of viscosity on miracidial and cercarial speed. Reynolds numbers, which describe the ratio of inertial to viscous forces exerted on an aquatic organism, were <1 across treatments. Q10 values were <2 when comparing viscosity treatments at 20 °C and 30 °C, further supporting the influence of viscosity on miracidial and cercarial speed. Given that both larval stages have limited energy reserves and infection takes considerable energy, successful transmission depends on both speed and lifespan. We coupled our speed data with mortality measurements across temperatures and discovered that the theoretical maximum distance travelled increased with temperature and decreased with viscosity for both larval stages. Thus, our results suggest that S. mansoni transmission is high during warm times of the year, partly due to improved swimming performance of the free-living larval stages, and that increases in temperature variation associated with climate change might further increase transmission.

Mapping the risk for transmission of urban schistosomiasis in the Brazilian Northeast.

This is an analysis of the risk of schistosomiasis transmission in the city of Recife in the Northeast of Brazil based on the number of schistosomiasis cases (Schistosoma mansoni) registered for the period 2007-2017 together with data resulting from active search of breeding sites of the Biomphalaria snail intermediate host. The analyses were performed using Kernel Density Estimation (KDE), SaTScan and Map Algebra methodology using human socio-demographic data and biotic and abiotic data from the snail breeding sites. Investigating 44 breeding sites resulted in a total of 3.800 snails, 31.8% of which were positive for S. mansoni DNA. These data were considered in relation to total of 652 schistosomiasis cases. The KDE showed two high-risk and two medium-risk clusters, while three significant clusters were identified by SaTScan. Combining these data with the Map Algebra methodology showed that all high-risk neighbourhoods had breeding sites with snails positive for S. mansoni. It was concluded that schistosomiasis transmission cannot be controlled without basic sanitation and sewage management in the presence of Biomphalaria snails. The technique of Map Algebra was found to be fundamental for the analysis and demonstration of areas with a high probability of schistosomiasis transmission.