Human Schistosoma Research Articles

Serological evaluation of the schistosome’s secretory enzyme phytochelatin synthase and phosphoglycerate mutase for the detection of human Schistosoma japonicum infection

Secretory enzymes from Schistosoma japonicum are promising candidate antigens in the diagnosis of schistosomiasis. Our previous studies have proven that thioredoxin peroxidase-1 (SjTPx-1) is useful for the detection of this parasitic disease in humans, water buffaloes, and dogs. In this study, we evaluated two more secretory enzymes namely phosphoglycerate mutase (SjPGM) and phytochelatin synthase (SjPCS) with SjTPx-1 as the reference antigen. SjPGM was shown to have good diagnostic potentials in animal samples in previous studies, whereas SjPCS was chosen because of its absence in the mammalian hosts. Serum samples including 96 endemic negative controls, 107 schistosomiasis japonica positive samples, and 31 samples positive for other parasitic trematode infections (Clonorchis sinensis, Opisthorchis viverrini, Paragonimus westermani) were tested with the antigens using enzyme-linked immunosorbent assay. Results showed that SjPCS detected more positive samples and had fewer cross-reactions than SjPGM. With 85.05% sensitivity and 93.55% specificity, SjPCS can therefore be used in the detection of human schistosomiasis.

Performance of a rapid immuno-chromatographic test (Schistosoma ICT IgG-IgM) for detecting Schistosoma-specific antibodies in sera of endemic and non-endemic populations

BackgroundSchistosomiasis, an acute and chronic parasitic disease caused by human pathogenic Schistosoma species, is a neglected tropical disease affecting more than 220 million people worldwide.For diagnosis of schistosomiasis, stool and urine microscopy for egg detection is still the recommended method, however sensitivity of these methods is limited. Therefore, other methods like molecular detection of DNA in stool, detection of circulating cathodic antigen in urine or circulating anodic antigen in urine and serum, as well as serological tests have gained more attention. This study examines the sensitivity and specificity of a rapid diagnostic test based on immunochromatography (Schistosoma ICT IgG-IgM, LD Bio, Lyon, France) for simultaneous detection of specific IgG and IgM antibodies in serum, against Schistosoma spp. in endemic and non-endemic populations.Methodology/Principal findingsFrozen banked serum samples from patients with confirmed schistosomiasis, patients with other helminth infections, patients with seropositive rheumatoid arthritis and healthy blood donors were used to assess the sensitivity and the specificity of the Schistosoma ICT IgG-IgM rapid diagnostic test.The test showed a sensitivity of 100% in patients with parasitologically confirmed schistosomiasis, irrespective of the species (S. mansoni, S. haematobium, S. japonicum, S. mekongi). In healthy blood donors and patients with rheumatoid factor positive rheumatoid arthritis from Europe, specificity was 100%. However, in serum samples of patients with other tissue invasive helminth infections, the test showed some cross-reactivity, resulting in a specificity of 85%.Conclusion/SignificanceWith its high sensitivity, the Schistosoma ICT IgG-IgM rapid diagnostic test is a suitable screening test for detection of Schistosoma specific antibodies, including S. mekongi. However, in populations with a high prevalence of co-infection with other tissue invasive helminths, positive results should be confirmed with other diagnostic assays due to the test’s imperfect specificity.

Epidemiological trends for human schistosomiasis prevalence in Hubei Province from 2004 to 2018 based on Joinpoint regression analysis

To analyze the trends of human schistosomiasis prevalence in Hubei Province from 2004 to 2018, so as to provide the evidence for formulating the schistosomiasis elimination strategy in the province. All data pertaining to human schistosomiasis prevalence in Hubei Province were collected from 2004 to 2018, and the trends for changes in seroprevalence, egg-positive rate and prevalence of human Schistosoma japonicum infection were analyzed using a Joinpoint regression model. Both of the numbers of residents seropositive and egg-positive for S. japonicum infections appeared a tendency towards a decline in Hubei Province from 2004 to 2018, and the prevalence of human S. japonicum infections reduced from 6.85% in 2004 to 0 in 2018. Joinpoint regression analysis showed that the prevalence of human S. japonicum infections appeared an overall tendency towards a reduction in Hubei Province from 2004 to 2018 [average annual percent change (AAPC) = -24.1%, P < 0.01], and the trends for the reduction were both significant during the period from 2004 to 2006 [annual percent change (APC) = -35.1%, P < 0.01] and from 2006 to 2018 (APC = -22.1%, P < 0.01). The prevalence of human S. japonicum infections appeared a tendency towards a decline in islet (AAPC = -25.1%, P < 0.01), inner embankment (AAPC = -26.4%, P < 0.01) and hilly subtypes of schistosomiasis-endemic areas (AAPC = -32.5%, P < 0.01) of Hubei Province from 2004 to 2018, and the prevalence all appeared a tendency towards a decline during the infection control stage (from 2004 to 2008), the transmission control stage (from 2009 to 2013) and the transmission interruption stage (from 2014 to 2018) (AAPC = -28.0%, -24.4% and -63.8%, all P values < 0.01). The seroprevalence of human S. japonicum infections appeared an overall tendency towards a decline in Hubei Province from 2004 to 2018 (AAPC = -14.5%, P < 0.01), and the trends for the reduction were both significant during the period from 2004 to 2012 (APC = -8.4%, P < 0.01) and from 2012 to 2018 (APC = -22.1%, P < 0.01). In addition, the egg-positive rate of human S. japonicum infections appeared an overall tendency towards a decline in Hubei Province from 2004 to 2018 (AAPC = -30.6%, P < 0.05), and the trend for the reduction was significant during the period from 2007 to 2014 (APC = -15.5%, P < 0.01). The prevalence of human schistosomiasis appeared a tendency towards a decline in Hubei Province from 2004 to 2018, and the islet and inner embankment subtypes of endemic areas are a high priority for schistosomiasis control during the stage moving towards elimination in Hubei Province.

Population Genetic Structure and Hybridization of Schistosoma haematobium in Nigeria.

Background: Schistosomiasis is a major poverty-related disease caused by dioecious parasitic flatworms of the genus Schistosoma with a health impact on both humans and animals. Hybrids of human urogenital schistosome and bovine intestinal schistosome have been reported in humans in several of Nigeria’s neighboring West African countries. No empirical studies have been carried out on the genomic diversity of Schistosoma haematobium in Nigeria. Here, we present novel data on the presence and prevalence of hybrids and the population genetic structure of S. haematobium. Methods: 165 Schistosoma-positive urine samples were obtained from 12 sampling sites in Nigeria. Schistosoma haematobium eggs from each sample were hatched and each individual miracidium was picked and preserved in Whatman® FTA cards for genomic analysis. Approximately 1364 parasites were molecularly characterized by rapid diagnostic multiplex polymerase chain reaction (RD-PCR) for mitochondrial DNA gene (Cox1 mtDNA) and a subset of 1136 miracidia were genotyped using a panel of 18 microsatellite markers. Results: No significant difference was observed in the population genetic diversity (p > 0.05), though a significant difference was observed in the allelic richness of the sites except sites 7, 8, and 9 (p < 0.05). Moreover, we observed two clusters of populations: west (populations 1–4) and east (populations 7–12). Of the 1364 miracidia genotyped, 1212 (89%) showed an S. bovis Cox1 profile and 152 (11%) showed an S. haematobium cox1 profile. All parasites showed an S. bovis Cox1 profile except for some at sites 3 and 4. Schistosoma miracidia full genotyping showed 59.3% of the S. bovis ITS2 allele. Conclusions: This study provides novel insight into hybridization and population genetic structure of S. haematobium in Nigeria. Our findings suggest that S. haematobium x S. bovis hybrids are common in Nigeria. More genomic studies on both human- and animal-infecting parasites are needed to ascertain the role of animals in schistosome transmission.

Contrasting epidemiology of urogenital schistosomiasis among pastoral communities surrounding three Ramsar wetland in Nigeria.

Suspected changes in the epidemiology of schistosomiasis due to several hybridization reports between human and livestock Schistosoma speciesin Africa calls for epidemiological investigations among potential high-risk groups and sites. Althoughthe use of wetlands for pastoralism has been linked to schistosomiasis, there is limited information on the epidemiology of the disease among pastoralists in Nigeria. In this study, urine samples from 355 participants from pastoral communities settled around three Ramsar wetlands (Wetlands of International Importance) in Nigeria, (Dagona Sanctuary, Maladumba, and Pandam-Wase) were screened for the eggs of Schistosoma haematobium. Only participants in the Dagona Sanctuary were infected with 34.2% prevalence. Macrohematuria was however observed in some individuals at the Dagona Sanctuary wetland (2.5%) and Maladumba (2.8%). Regular praziquantel administration, functional health care facilities and awareness about schistosomiasis were contributory factors to the contrasting epidemiology of the disease among the study population. Schistosomiasis control requires the inclusion of pastoral and nomadic communities in mass drug administration of praziquantel based on a community-directed intervention strategy.

Epidemiological trends of schistosomiasis in Poyang County of Jiangxi Province from 2004 to 2020 based on the Joinpoint regression model

To analyze the dynamic changes of schistosomiasis in Poyang County of Jiangxi Province from 2004 to 2020, so as to provide insight into the development of the schistosomiasis elimination strategy. Schistosomiasis control data were captured from Poyang County from 2004 to 2020, and the epidemiological data of schistosomiasis were collected from national schistosomiasis surveillance sites in Poyang County from 2005 to 2020. The endemic status of schistosomiasis was analyzed in Poyang County from 2004 to 2020, and a Joinpoint regression analysis was performed to investigate the trends of schistosomiasis in Poyang County from 2004 to 2020. The sero-prevalence and egg-prevalence of human Schistosoma japonicum infections reduced from 24.39% (24 976/102 397) and 4.53% (259/5 721) in 2004 to 5.37% (2 421/45 100) [annual percent change (APC) = average annual percent change (AAPC) = -8.64%] and 0 (0/3 963) in 2020 (APC = AAPC = -32.07%) in Poyang County, and the trends were both significant (both P < 0.01). The sero-prevalence of S. japonicum infections reduced from 1.21% (294/24 332) in bovines in 2013 to 0.58% (35/5 999) in 2020 in Poyang County, with one turning point (AAPC = -8.20%, P > 0.05). There were no townships or villages with emerging snail habitats in Poyang County from 2004 to 2020, and there were three turning points of trend in the proportion of snail areas detected in total snail areas (AAPC = -2.30%, P > 0.01). The sero-prevalence and adjusted prevalence of S. japonicum infections reduced from 60.82% (742/1 220) and 10.16% (124/1 220) in local residents in 2005 to 5.73% (70/1 221) and 0 in 2020 in national schistosomiasis surveillance sites of Poyang County, and the trends for sero-prevalence (APC = AAPC = 17.47%, P < 0.01) and adjusted prevalence of S. japonicum infections (APC = AAPC = -44.92%, P < 0.01) were both statistically significant. S. japonicum infections were identified in 10 (2005) and 2 local livestock (2007), with prevalence of 10.00% (10/100) and 13.33% (2/15), respectively, and S. japonicum infections were detected in snails in 2008 and 2009; however, no positive samples of mixed O. hupensis were detected by loop-mediated isothermal amplification. The endemic situation of schistosomiasis control had remarkably reduced in Poyang County from 2004 to 2020; however, there are still challenges for consolidating schistosomiasis control achievements and even elimination of schistosomiasis.

Transmission potential of human schistosomes can be driven by resource competition among snail intermediate hosts

Predicting and disrupting transmission of human parasites from wildlife hosts or vectors remains challenging because ecological interactions can influence their epidemiological traits. Human schistosomes, parasitic flatworms that cycle between freshwater snails and humans, typify this challenge. Human exposure risk, given water contact, is driven by the production of free-living cercariae by snail populations. Conventional epidemiological models and management focus on the density of infected snails under the assumption that all snails are equally infectious. However, individual-level experiments contradict this assumption, showing increased production of schistosome cercariae with greater access to food resources. We built bioenergetics theory to predict how resource competition among snails drives the temporal dynamics of transmission potential to humans and tested these predictions with experimental epidemics and demonstrated consistency with field observations. This resource-explicit approach predicted an intense pulse of transmission potential when snail populations grow from low densities, i.e., when per capita access to resources is greatest, due to the resource-dependence of cercarial production. The experiment confirmed this prediction, identifying a strong effect of infected host size and the biomass of competitors on per capita cercarial production. A field survey of 109 waterbodies also found that per capita cercarial production decreased as competitor biomass increased. Further quantification of snail densities, sizes, cercarial production, and resources in diverse transmission sites is needed to assess the epidemiological importance of resource competition and support snail-based disruption of schistosome transmission. More broadly, this work illustrates how resource competition can sever the correspondence between infectious host density and transmission potential.

Reducing disease and producing food: Effects of 13 agrochemicals on snail biomass and human schistosomes

Abstract Agricultural expansion is predicted to increase agrochemical use two to fivefold by 2050 to meet food demand. Experimental evidence suggests that agrochemical pollution could increase snails that transmit schistosomiasis, a disease impacting 250 million people, yet most agrochemicals remain unexamined. Here we experimentally created &gt;100 natural wetland communities to quantify the relative effects of fertilizer, six insecticides (chlorpyrifos, terbufos, malathion, λ‐cyhalothrin, permethrin and esfenvalerate), and six herbicides (acetochlor, alachlor, metolachlor, atrazine, propazine and simazine) on two snail genera responsible for 90% of global schistosomiasis cases. We identified four of six insecticides (terbufos, permethrin, chlorpyrifos and esfenvalerate) as high risk for increasing snail biomass by reducing snail predators. Hence, malathion and λ‐cyhalothrin might be useful for improving food production without increasing schistosomiasis. This top‐down effect of insecticides on predators was so strong that the effects of herbicides on schistosomiasis risk were masked in the presence of predators because there were so few snails. In the absence of snail predators, herbicide effects on snails were generally negative by reducing submerged vegetation Hydrilla verticillata. The exception was that atrazine and acetochlor significantly increased the biomass of infected snails and total snails respectively. Like insecticides, fertilizer had strong positive effects on snail populations. Fertilizer increased both snail habitat (submerged vegetation) and snail food (periphyton), but of these two pathways, the increases in snail habitat resulted in greater snail population growth. Total snail biomass was positively associated with both infected snail biomass and parasite production and thus human infection risk. Synthesis and applications. Our findings suggest that fertilizers and insecticides generally have consistently higher chances of increasing human schistosomiasis than herbicides in natural communities. Furthermore, our results highlight the need to identify other low risk insecticides, which might help reduce crop pests without increasing snails and thus risk of schistosomiasis.

Divergent effects of invasive macrophytes on population dynamics of a snail intermediate host of Schistosoma Mansoni

Vectors and intermediate hosts of globally impactful human parasites are sensitive to changes in the ecological communities in which they are embedded. Sites of endemic transmission of human schistosome can also be invaded by nonnative species, especially aquatic plants (macrophytes). We tested the effects on macrophyte invasions on experiment snail and schistosome populations created in 100 L mesocosm tanks. We established macrophyte-free mesocosms and those containing one of four widespread macrophyte species that are inedible to snails (duckweed, hornwort, water lettuce, or water hyacinth) and then tracked edible resources (periphyton algae) and the abundance, reproduction, and infection of snail intermediate hosts for 16 weeks. We predicted that the three floating macrophytes would reduce periphyton, thereby reducing snail reproduction, abundance, and infections. In contrast, we predicted that hornwort, which is submerged and provides substrate for periphyton growth, would increase snail reproduction and abundance. As predicted, all floating macrophytes decreased periphyton, but only water hyacinth significantly decreased snail reproduction and abundance. Snail abundance increased significantly only with water lettuce. We hypothesize that this unanticipated increase in snails occurred because water lettuce produced abundant and/or high quality detritus, subsidizing snails despite low periphyton availability. Unfortunately, we detected too few infections to analyze. Aquatic macrophytes exert strong species-specific effects on snail populations. Therefore, efforts to manage invasive plants in endemic sites should evaluate changes in resources, snails, and transmission potential. We recommend caution with management efforts that produce large amounts of detritus, which might stimulate snail populations and therefore risk of human exposure.

Hybridized Zoonotic Schistosoma Infections Result in Hybridized Morbidity Profiles: A Clinical Morbidity Study amongst Co-Infected Human Populations of Senegal.

Hybridization of infectious agents is a major emerging public and veterinary health concern at the interface of evolution, epidemiology, and control. Whilst evidence of the extent of hybridization amongst parasites is increasing, their impact on morbidity remains largely unknown. This may be predicted to be particularly pertinent where parasites of animals with contrasting pathogenicity viably hybridize with human parasites. Recent research has revealed that viable zoonotic hybrids between human urogenital Schistosoma haematobium with intestinal Schistosoma species of livestock, notably Schistosoma bovis, can be highly prevalent across Africa and beyond. Examining human populations in Senegal, we found increased hepatic but decreased urogenital morbidity, and reduced improvement following treatment with praziquantel, in those infected with zoonotic hybrids compared to non-hybrids. Our results have implications for effective monitoring and evaluation of control programmes, and demonstrate for the first time the potential impact of parasite hybridizations on host morbidity.

Antischistosomal effects of Ficus carica leaves extract and/or PZQ on Schistosoma mansoni infected mice.

Currently, praziquantel (PZQ) is the only drug of choice used for treatment of human schistosomes because of its safety and broad-spectrum activity. It is reported that the repeated chemotherapy is complicated by the occurrence of drug resistance to schistosomiasis. So there is an urgent need to develop newdrug combinations therapy. The current study aimed to evaluate antischistosomal activity of F. carica leaves extract alone or in combination with PZQ on Schistosoma mansoni infected mice. Mice were experimentally infected with Schistosoma mansoni and orally administrated 6weeks' post-infection with Fig leaves extract and/or PZQ. Schistosoma mansoni (S. mansoni)-infected mice were separated into four groups: untreated (I), treated with PZQ in dose of 200mg/kg bw (II), treated with Fig leaves extract dose of 400mg/kg bw (III). Group IV was treated with dose of Fig leaves extract-PZQ as in groups II and III, respectively. The effect was detected parasitologically using ova count technique and oogram pattern in intestine and liver. The greatest antischistosomal effect was achieved using orally administered Fig leaves extract-PZQ as indicated by total worm burden, tissue egg count and oogram pattern. Fig leaves extract + PZQ induced the therapeutic efficacy over the PZQ dose alone in intestine and liver as shown by a complete absence of immature worms, a very high reduction in the total numbers of tissue egg load (59.81% vs. 61.43% & 67.96% vs. 73.46%), mature eggs (37.86 ± 1.4 vs. 34.14 ± 1.9) and increasing in the total number of dead eggs (62.14 ± 1.4vs.67.29 ± 1.76). The results suggested the curcumin in combination with PZQ as a strong schistosomicidal regimen againstS. mansoni. In addition, F. carica leaves extract is a promising for PZQ potentiating its antischistosomal action in animal model infected with S. mansoni. Therefore, the present work conclude that combined treatment has a synergetic effect and could be more promising in the management of schistosomiasis.

Prevalence of urogenital and intestinal schistosomiasis among school children in South-west Nigeria.

The risk of co-infection with Schistosoma haematobium and S. mansoni and the potential harmful effect on morbidity and control is enhanced by the overlapping distribution of both species in sub-Saharan Africa. Despite the reported high endemicity of both species in Nigeria, studies on the spread and effect of their mixed infection are limited. Therefore, a cross-sectional survey was conducted among school children in two communities in South-west Nigeria to investigate the prevalence of mixed human schistosome infection, intensity, and possible ectopic egg elimination. Urine and stool samples were collected from consenting school children in Ilie and Ore communities of Osun State, Nigeria. Schistosoma haematobium eggs were detected in urine using the urine filtration technique, while S. mansoni eggs were detected in stool using the Kato-Katz thick smear technique. The study enrolled 466 primary and secondary school children (211; 45.3% males vs. 255; 54.7% females; mean age 11.6 ± 3.16 years). The overall prevalence of schistosomiasis was 40% (185/466), with 19% (89/466) recording single S. haematobium infection while 9% (41/465) had a single S. mansoni infection. The geometric mean egg count for S. haematobium was 189.4 egg/10ml urine; 95% CI: range 115.9-262.9, while for S. mansoni, it was 115.7 epg; 95% CI: range 78.4-152.9. The prevalence of ectopic S mansoni (S. mansoni eggs in urine) was 4.7%, while no ectopic S. haematobium (S. haematobium eggs in stool) was recorded. Mixed infection of S. haematobium/S. mansoni had a prevalence of 9.5% (44/466). More females (54.5%) presented with S. haematobium/S. mansoni co-infection. For both parasites, males had higher infection intensity, with a significant difference observed with S. haematobium (p = 0.0004). Hematuria was significant in individuals with single S. haematobium infection (p = 0.002), mixed ectopic S. haematobium/S. mansoni (p = 0.009) and mixed S. haematobium/S. mansoni/ectopic S. mansoni (p = 0.0003). These findings suggest the probability of interspecific interactions between S. haematobium and S. mansoni. Scaling up of mass administration of praziquantel and control measures in the study areas is highly desirable.

Revisiting density-dependent fecundity in schistosomes using sibship reconstruction

The stability of parasite populations is regulated by density-dependent processes occurring at different stages of their life cycle. In dioecious helminth infections, density-dependent fecundity is one such regulatory process that describes the reduction in egg production by female worms in high worm burden within-host environments. In human schistosomiasis, the operation of density-dependent fecundity is equivocal and investigation is hampered by the inaccessibility of adult worms that are located intravascularly. Current understanding is almost exclusively limited to data collected from two human autopsy studies conducted over 40 years ago, with subsequent analyses having reached conflicting conclusions. Whether egg production is regulated in a density-dependent manner is key to predicting the effectiveness of interventions targeting the elimination of schistosomiasis and to the interpretation of parasitological data collected during monitoring and evaluation activities. Here, we revisit density-dependent fecundity in the two most globally important human Schistosoma spp. using a statistical modelling approach that combines molecular inference on the number of parents/adult worms in individual human hosts with parasitological egg count data from mainland Tanzania and Zanzibar. We find a non-proportional relationship between S. haematobium egg counts and inferred numbers of female worms, providing the first clear evidence of density-dependent fecundity in this schistosome species. We do not find robust evidence for density-dependent fecundity in S. mansoni because of high sensitivity to some modelling assumptions and the lower statistical power of the available data. We discuss the strengths and limitations of our model-based analytical approach and its potential for improving our understanding of density dependence in schistosomiasis and other human helminthiases earmarked for elimination.

Land use impacts on parasitic infection: a cross-sectional epidemiological study on the role of irrigated agriculture in schistosome infection in a dammed landscape

BackgroundWater resources development promotes agricultural expansion and food security. But are these benefits offset by increased infectious disease risk? Dam construction on the Senegal River in 1986 was followed by agricultural expansion and increased transmission of human schistosomes. Yet the mechanisms linking these two processes at the individual and household levels remain unclear. We investigated the association between household land use and schistosome infection in children.MethodsWe analyzed cross-sectional household survey data (n = 655) collected in 16 rural villages in August 2016 across demographic, socio-economic and land use dimensions, which were matched to Schistosoma haematobium (n = 1232) and S. mansoni (n = 1222) infection data collected from school-aged children. Mixed effects regression determined the relationship between irrigated area and schistosome infection presence and intensity.ResultsControlling for socio-economic and demographic risk factors, irrigated area cultivated by a household was associated with an increase in the presence of S. haematobium infection (odds ratio [OR] = 1.14; 95% confidence interval [95% CI]: 1.03–1.28) but not S. mansoni infection (OR = 1.02; 95% CI: 0.93–1.11). Associations between infection intensity and irrigated area were positive but imprecise (S. haematobium: rate ratio [RR] = 1.05; 95% CI: 0.98–1.13, S. mansoni: RR = 1.09; 95% CI: 0.89–1.32).ConclusionsHousehold engagement in irrigated agriculture increases individual risk of S. haematobium but not S. mansoni infection. Increased contact with irrigated landscapes likely drives exposure, with greater impacts on households relying on agricultural livelihoods.

A systematic literature review of schistosomiasis in urban and peri-urban settings.

BackgroundSchistosomiasis is a parasitic disease caused by trematode worms of the genus Schistosoma and belongs to the neglected tropical diseases. The disease has been reported in 78 countries, with around 290.8 million people in need of treatment in 2018. Schistosomiasis is predominantly considered a rural disease with a subsequent focus of research and control activities in rural settings. Over the past decades, occurrence and even expansion of schistosomiasis foci in peri-urban and urban settings have increasingly been observed. Rural–urban migration in low- and middle-income countries and subsequent rapid and unplanned urbanization are thought to explain these observations. Fifty-five percent (55%) of the world population is already estimated to live in urban areas, with a projected increase to 68% by 2050. In light of rapid urbanization and the efforts to control morbidity and ultimately achieve elimination of schistosomiasis, it is important to deepen our understanding of the occurrence, prevalence, and transmission of schistosomiasis in urban and peri-urban settings. A systematic literature review looking at urban and peri-urban schistosomiasis was therefore carried out as a first step to address the research and mapping gap.MethodologyFollowing the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic computer-aided literature review was carried out using PubMed, ScienceDirect, and the World Health Organization Database in November 2019, which was updated in March 2020. Only papers for which at least the abstract was available in English were used. Relevant publications were screened, duplicates were removed, guidelines for eligibility were applied, and eligible studies were reviewed. Studies looking at human Schistosoma infections, prevalence, and intensity of infection in urban and peri-urban settings were included as well as those focusing on the intermediate host snails.Principal findingsA total of 248 publications met the inclusion criteria. The selected studies confirm that schistosomiasis is prevalent in peri-urban and urban areas in the countries assessed. Earlier studies report higher prevalence levels in urban settings compared to data extracted from more recent publications, yet the challenge of migration, rapid uncontrolled urbanization, and resulting poor living conditions highlight the potential for continuous or even newly established transmission to take place.ConclusionsThe review indicates that schistosomiasis has long existed in urban and peri-urban areas and remains a public health problem. There is, however, a challenge of comparability of settings due to the lack of a clear definition of what constitutes urban and peri-urban. There is a pressing need for improved monitoring of schistosomiasis in urban communities and consideration of treatment strategies.

Immune Evasion Strategies of Schistosomes.

Human schistosomes combat the unique immune systems of two vastly different hosts during their indirect life cycles. In gastropod molluscs, they face a potent innate immune response composed of variable immune recognition molecules and highly phagocytic hemocytes. In humans, a wide variety of innate and adaptive immune processes exist in proximity to these parasites throughout their lifespan. To survive and thrive as the second most common parasitic disease in humans, schistosomes have evolved many techniques to avoid and combat these targeted host responses. Among these techniques are molecular mimicry of host antigens, the utilization of an immune resistant outer tegument, the secretion of several potent proteases, and targeted release of specific immunomodulatory factors affecting immune cell functions. This review seeks to describe these key immune evasion mechanisms, among others, which schistosomes use to survive in both of their hosts. After diving into foundational observational studies of the processes mediating the establishment of schistosome infections, more recent transcriptomic and proteomic studies revealing crucial components of the host/parasite molecular interface are discussed. In order to combat this debilitating and lethal disease, a comprehensive understanding of schistosome immune evasion strategies is necessary for the development of novel therapeutics and treatment plans, necessitating the discussion of the numerous ways in which these parasitic flatworms overcome the immune responses of both hosts.

Fine-scale heterogeneity in Schistosoma mansoni force of infection measured through antibody response

Schistosomiasis is among the most common parasitic diseases in the world, with over 142 million people infected in low- and middle-income countries. Measuring population-level transmission is centrally important in guiding schistosomiasis control programs. Traditionally, human Schistosoma mansoni infections have been detected using stool microscopy, which is logistically difficult at program scale and has low sensitivity when people have low infection burdens. We compared serological measures of transmission based on antibody response to S. mansoni soluble egg antigen (SEA) with stool-based measures of infection among 3,663 preschool-age children in an area endemic for S. mansoni in western Kenya. We estimated force of infection among children using the seroconversion rate and examined how it varied geographically and by age. At the community level, serological measures of transmission aligned with stool-based measures of infection (ρ = 0.94), and serological measures provided more resolution for between-community differences at lower levels of infection. Force of infection showed a clear gradient of transmission with distance from Lake Victoria, with 94% of infections and 93% of seropositive children in communities <1.5 km from the lake. Force of infection increased through age 3 y, by which time 65% (95% CI: 53%, 75%) of children were SEA positive in high-transmission communities-2 y before they would be reached by school-based deworming programs. Our results show that serologic surveillance platforms represent an important opportunity to guide and monitor schistosomiasis control programs, and that in high-transmission settings preschool-age children represent a key population missed by school-based deworming programs.

Future schistosome hybridizations: Will all Schistosoma haematobium hybrids please stand-up!

nterrogating the genetic make-up of schistosome larvae (i.e. eggs, miracidia and cercariae) originating from definitive or intermediate snail hosts with molecular DNA methods has, by noting unexpected inter-species hybrids, started a revolution in our appraisal of African schistosomiasis [1-4]. Here, two dominant species of human schistosome exist, Schistosoma haematobium and S. mansoni, which are transmitted by specific intermediate freshwater snails, Bulinus spp. for the former and Biomphalaria spp. for the latter. The two schistosomes cause either urogenital or intestinal schistosomiasis, respectively [5] and depending on local snail distributions, schistosome transmission zones in the aquatic habitat may or may not overlap [6]. Within the S. haematobium group, a further 8 sister species are described with S. intercalatum and S. guineensis of medical importance, causing intestinal schistosomiasis while others, such as S. bovis, S. curassoni and S. mattheei occur in livestock, with the remaining species infecting wildlife. Schistosoma mattheei is also of medical interest for occasional infection and associated disease [7]. In contrast, S. mansoni has a single sister species, S. rodhaini, typically found in small rodents which can hybridise with S. mansoni, if given sufficient opportunity [2].

Modelling how resource competition among snail hosts affects the mollusciciding frequency and intensity needed to control human schistosomes

Abstract Ecological interactions among intermediate hosts or vectors of human pathogens can enhance or hinder control efforts. However, we currently lack quantitative frameworks to predict how interactions among host physiology, ecology and control effort shape human disease risk. We explore this approach for human schistosomiasis, a major, historically neglected tropical disease. A recent re‐emphasis on snail host control using molluscicides highlights the need to re‐evaluate the ecological mechanisms driving emergence of schistosome cercariae, the life stage that directly infects humans. We integrate physiology, resource competition and control using individual‐based models based on general metabolic theory, Dynamic Energy Budget theory, to simulate human infectious schistosome density under molluscicide scenarios varying in frequency and intensity throughout a 150‐day transmission season. Without molluscicide control, our model predicts intense resource competition among hosts and large and early parasite peaks under algae and detritus resources. Consistent monthly control, as recommended by the WHO, can work if intense, that is, &gt;90% host mortality. In contrast, one‐off, intense and early mollusciciding induces large delayed rebounds in parasites by releasing the few remaining snails from resource competition. Our simulations confirm the WHO recommendation that frequent mollusciciding can disrupt transmission, but contradict recent suggestions for infrequent mollusciciding, for example, annually, which can backfire because relaxed resource competition among hosts stimulates parasite production. Our results identify resource competition as a key ecological mechanism driving parasite population intensity for schistosome habitats across ecosystems. Our results show resource ecology models can identify peaks in parasite density. More generally, resource competition among hosts may complicate efforts to control infected snail host densities in the field and thus disease risk through culling or mortality‐based interventions. Connecting individuals to community and disease dynamics with resource ecology can inform better field control strategies and help managers avoid unintended consequences for human health. A free Plain Language Summary can be found within the Supporting Information of this article.

Evaluating the Ecology and Distribution of Snail Hosts of Schistosoma at the Water Bodies in Ihitte-Uboma Area of Imo State

Intermediate snail host of Schistosoma species are known to exist and constitute public health problems in Imo state. Effects on this study were devoted to evaluate the ecology and distribution of the snail hosts of Schistosoma species at the water bodies of Ihitte Uboma local Government area and this was researched during the months of June and September, 2015. A total of 600 pulmonate or lunged snails were collected using scoop net technique from different water bodies in five villages, out of these, 345 (57.5%) were dissected and screened for cercariae of human Schistosomes 67 (19.4%) tested positive. The snail infected were Bulinus species 55 (82.1%) and Biomphalaria Pfeifferi (17.9%), out of the Bulinus species, Bulinus globosus recorded the widest ecological range, highest distribution and infection rate of 44.8% followed by Bulinus truncatus (22.4%). The other two genera Lymnaea spp and Melanoides spp encountered in the study did not test positive for cercariae. Environmental modifications such as water resources development schemes in the area are some of the ecological and epidemiological risk factor promoting the spread of the snails. Statistically, presence of urinary and intestinal Schistosomiasis becomes indicated in Ihitte Uboma L.G.A. Regular and timing mollusciciding, malacological and public health education are therefore recommended and imperative.