Infected Snails Research Articles

Schistosomiasis Consortium for Operational Research and Evaluation (SCORE): Its Foundations, Development, and Evolution.

.The Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) was established in late 2008 to conduct operational research that would inform practices related to the control and elimination of schistosomiasis. This article traces SCORE’s beginnings and underpinnings. These include an emphasis on openness and contributing to the development of a cohesive schistosomiasis control community, building linkages between researchers and national programs, and focusing on answering questions that will help Neglected Tropical Disease program managers to better control and eliminate schistosomiasis. It describes the development and implementation of SCORE’s multiple projects. SCORE began by drawing on advice from a broad range of experts by holding wide-ranging meetings that informed the priorities and protocols for SCORE research. SCORE’s major efforts included large, multicountry field studies comparing multiple strategies for mass drug administration with praziquantel, assessment of approaches to elimination, evaluation of a point-of-care assay for field mapping Schistosoma mansoni, and increasing the sensitivity of a laboratory-based diagnostic. SCORE also supported studies on morbidity due to schistosomiasis, quantification of vector snails and the detection of schistosome infections in snails, and changes in schistosome population genetics under praziquantel drug pressure. SCORE data and specimens are archived and will remain available for future research. Although much remains to be carried out, our hope is that through the already published articles and SCORE results described in this supplement, we will have provided a body of evidence to assist policy makers in the development of judicious guidelines for the control and elimination of schistosomiasis.

Snail-Related Contributions from the Schistosomiasis Consortium for Operational Research and Evaluation Program Including Xenomonitoring, Focal Mollusciciding, Biological Control, and Modeling.

.The Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) was created in 2008 to answer questions of importance to program managers working to reduce the burden of schistosomiasis in Africa. In the past, intermediate host snail monitoring and control was an important part of integrated schistosomiasis control. However, in Africa, efforts to control snails have declined dramatically over the last 30 years. A resurgence of interest in the control of snails has been prompted by the realization, backed by a World Health Assembly resolution (WHA65.21), that mass drug administration alone may be insufficient to achieve schistosomiasis elimination. SCORE has supported work on snail identification and mapping and investigated how xenomonitoring techniques can aid in the identification of infected snails and thereby identify potential transmission areas. Focal mollusciciding with niclosamide was undertaken in Zanzibar and Côte d’Ivoire as a part of elimination studies. Two studies involving biological control of snails were conducted: one explored the association of freshwater riverine prawns and snail hosts in Côte d’Ivoire and the other assessed the current distribution of Procambarus clarkii, the invasive Louisiana red swamp crayfish, in Kenya and its association with snail hosts and schistosomiasis transmission. SCORE also supported modeling studies on the importance of snail control in achieving elimination and a meta-analysis of the impact of molluscicide-based snail control programs on human schistosomiasis prevalence and incidence. SCORE’s snail control studies contributed to increased investment in building capacity, and specimens collected during SCORE research deposited in the Schistosomiasis Collections at the Natural History Museum (SCAN) will provide a valuable resource for the years to come.

Effect of integrated schistosomiasis control measures in Hunan Province from 2004 to 2019

To examine the effect of the integrated schistosomiasis control measures in Hunan Province from 2004 to 2019, so as to provide insights into the development of the schistosomiasis elimination strategy. The integrated schistosomiasis control measures implemented by the health, agriculture, water resources, forestry, land and resources sectors were retrospectively collected in Hunan Province from 2004 to 2019, and the completion of each measure, cost of control measures, Schistosoma japonicum infections in humans and bovines, and snail status were analyzed each year. An index system for assessing the integrated schistosomiasis control effect was constructed using the Delphi method to calculate the integrated schistosomiasis control effect index. In addition, a cost-effect analysis was performed in terms of the decline in the prevalence of S. japonicum infections in humans and bovines, areas with snails in inner embankments, and areas with infected snails. A total of 7 110 926 500 Yuan were invested into the integrated schistosomiasis control program of Hunan Province from 2004 to 2019. During the 16-year period, a total of 277 437.12 hm2 snail habitats received molluscicidal treatments, 6 927 230 person-times given expanded chemotherapy, 2 116 247 bovine-times given expanded chemotherapy, 954 850 harmless toilets built, 290 359 bovines fenced, 136 666 bovines eliminated, 141 905 machines used to replace bovines, 39 048.63 hm2 water lands improved as dry lands, 724.12 km irrigation regions improved, 3 994 300 populations covered with safe water, 191 102.89 hm2 forests planted and 38 535.27 hm2 lands leveled. The prevalence of S. japonicum infections was 4.29% in humans and 4.48% in bovines in Hunan Province in 2004, with 2 449.37 hm2 snail habitats in inner embankments and 3 423.74 hm2 infected snail areas. In 2019, the prevalence of S. japonicum infections reduced to 0 in both humans and bovines, and areas of snail habitats reduced to 540.92 hm2 (77.92% reductions), while the areas with infected snails reduced to 0. The overall integrated schistosomiasis control effect index appeared a tendency towards a rise over years since 2004, and the integrated schistosomiasis control effect index was 97.35 in 2019; the annual mean costs for a 1% reduction in the prevalence of S. japonicum infections in 100 populations and 100 bovines were 70.11 Yuan and 4 204.78 Yuan, and the annual mean costs for a 1% reduction in the snail areas in inner embankments and infected snail areas were 2 010.20 Yuan and 1 298.09 Yuan, respectively. The integrated control measures achieve remarkable effectiveness for schistosomiasis control in Hunan Province, with a remarkable decline in the prevalence of S. japonicum infections in humans and bovines and great shrinking of snail areas in inner embankments and infected snail areas. Adequate fund investment is required to improve the integrated schistosomiasis control measures and consolidate the control achievements.

Temporal transcriptome change of Oncomelania hupensis revealed by Schistosoma japonicum invasion

BackgroundThe freshwater snail Oncomelania hupensis is the obligate intermediate host for Schistosoma japonicum in China. Transcriptomic examination of snail–schistosome interactions can provide valuable information of host response at physiological and immune levels.MethodsTo investigate S. japonicum-induced changes in O. hupensis gene expression, we utilized high-throughput sequencing to identify transcripts that were differentially expressed between infected snails and their uninfected controls at two key time-point, Day 7 and Day 30 after challenge. Time-series transcriptomic profiles were analyzed using R package DESeq 2, followed by GO, KEGG and (weighted gene correlation network analysis) WGCNA analysis to elucidate and identify important molecular mechanism, and subsequently understand host–parasite relationship. The identified unigenes was verified by bioinformatics and real-time PCR. Possible adaptation molecular mechanisms of O. hupensis to S. japonicum challenge were proposed.ResultsTranscriptomic analyses of O. hupensis by S. japonicum invasion yielded billion reads including 92,144 annotated transcripts. Over 5000 differentially expressed genes (DEGs) were identified by pairwise comparisons of infected libraries from two time points to uninfected libraries in O. hupensis. In total, 6032 gene ontology terms and 149 KEGG pathways were enriched. After the snails were infected with S. japonicum on Day 7 and Day 30, DEGs were shown to be involved in many key processes associated with biological regulation and innate immunity pathways. Gene expression patterns differed after exposure to S. japonicum. Using WGCNA, 16 modules were identified. Module-trait analysis identified that a module involved in RNA binding, ribosome, translation, mRNA processing, and structural constituent of ribosome were strongly associated with S. japonicum invasion. Many of the genes from enriched KEGG pathways were involved in lysosome, spliceosome and ribosome, indicating that S. japonicum invasion may activate the regulation of ribosomes and immune response to infection in O. hupensis.ConclusionsOur analysis provided a temporally dynamic gene expression pattern of O. hupensis by S. japonicum invasion. The identification of gene candidates serves as a foundation for future investigations of S. japonicum infection. Additionally, major DEGs expression patterns and putative key regulatory pathways would provide useful information to construct gene regulatory networks between host-parasite crosstalk.

First Egyptian record of the eye fluke (Philophthalamus palpebrarum) transmitted by Melanoides tuberculata snail and its experimental life cycle

The present study has been recorded, for the first time, cercariae of Philophthalamus palpebrarum (Trematoda: Philophthalmidae occurring in the birds-eye) emerged from naturally infected Melanoides tuberculata snails collected from Giza Governorate, Egypt, and succeeded to complete its life cycle experimentally. The adult worm was extracted from the conjunctival sac of the chicken eyes after 35-40 days post experimental infection by pipetting 10-15 excysted metacercariae into each eye orbit of (1-3 days old chicks). The worms were identified as Philophthalamus palpebrarum based on the morphological characteristics and the comparison with the previous descriptions in the literature. They were small, the body length, 5.48 mm (4.6 - 6.1) and its width 1.60 mm (1.32 - 1.9) and the surface of the body is smooth and lacks spination. The morphological characteristics of the developmental stages, from cercariae to adults, of this eye fluke, were described. It can be concluded that this eye fluke was described as Philophathalamus palpebrarum and the Melanoides tuberculata snails emphasized as its intermediate host in natural and experimental infection for the first time in Egypt. From this study, it is recommended to pay more attention to this parasite as a zoonotic disease to avoid the risk factor of this parasite to humans.

Spatiotemporal distribution of Oncomelania hupensis snail habitats in Anhui Province

To investigate the spatiotemporal distribution of Oncomelania hupensis snails and infected snails in the endemic areas of schistosomiasis in Anhui Province. Based on the snail survey data in Anhui Province in 2016, the distribution of snails and infected snails were analyzed, and the spatial distribution of snails and spatial cluster patterns of infected snails were investigated in snail habitats in Anhui Province from 1950 to 2016. A total of 22 757 snail habitats and 5 004 infected snail habitats were identified in Anhui Province from 1950 to 2016, which appeared single-peak and double-peak patterns, with an inflection point seen in 1970. There were 141 000 hm2 historically accumulative snail habitats, 88.08% of which were firstly identified from 1950 to 1979, and totally 114 500 hm2 snail habitats were eradicated, 77.17% of which were eradicated from 1970 to 1999. There were 4 830 snail habitats identified until 2016, in which 1 051 were once detected with infected snails. In addition, 78.12% of current snail habitats had been present for over 40 years, and infected snails had been eliminated in 65.75% of the infected snail habitats within 10 years. There was a spatial autocorrelation of the living snail density in current snail habitats in Anhui Province (Moran's I = 0.196, Z = 139.63, P < 0.001), and local hotspot analysis showed spatial clusters of living snails density in snail habitats, with high-value clusters in south of the Yangtze River and low-value clusters in north of the Yangtze River. The 21 high-value clusters of living snail density with statistical significance were distributed along the Yangtze River basin and its branches. Spatiotemporal scan analysis revealed spatiotemporal clusters of infected snails in 4 current snail habitats. The current snail habitats have been present for a long period of time, and snails are difficult to be eliminated by chemical treatment alone, which requires the combination of environment improvements. There are spatial clusters of living snail density in current snail habitats in Anhui Province. The epidemic factors and risk of human and animal infections still remain in some clusters of historical infected snail habitats revealed by spatiotemporal scan analysis, which should be consid- ered as the key target areas for snail control in Anhui Province.

Determining the viability of Schistosoma mansoni cercariae using fluorescence assays: An application for water treatment.

BackgroundSchistosome cercariae are the human-infectious stage of the Schistosoma parasite. They are shed by snail intermediate hosts living in freshwater, and penetrate the skin of the human host to develop into schistosomes, resulting in schistosomiasis infection. Water treatment (e.g. filtration or chlorination) is one way of cutting disease transmission; it kills or removes cercariae to provide safe water for people to use for activities such as bathing or laundry as an alternative to infested lakes or rivers. At present, there is no standard method for assessing the effectiveness of water treatment processes on cercariae. Examining cercarial movement under a microscope is the most common method, yet it is subjective and time-consuming. Hence, there is a need to develop and verify accurate, high-throughput assays for quantifying cercarial viability.MethodWe tested two fluorescence assays for their ability to accurately determine cercarial viability in water samples, using S. mansoni cercariae released from infected snails in the Schistosomiasis Collection at the Natural History Museum, London. These assays consist of dual stains, namely a vital and non-vital dye; fluorescein diacetate (FDA) and Hoechst, and FDA and Propidium Iodide. We also compared the results of the fluorescence assays to the viability determined by microscopy.ConclusionBoth fluorescence assays can detect the viability of cercariae to an accuracy of at least 92.2% ± 6.3%. Comparing the assays to microscopy, no statistically significant difference was found between the method’s viability results. However, the fluorescence assays are less subjective and less time-consuming than microscopy, and therefore present a promising method for quantifying the viability of schistosome cercariae in water samples.

Biochemical and apoptotic changes in the nervous and ovotestis tissues of Biomphalaria alexandrina following infection with Schistosoma mansoni

Infection with trematodes produces physiological and behavioural changes in intermediate snail hosts. One response to infection is parasitic castration, in which energy required for reproduction of the host is thought to be redirected to promote development and multiplication of the parasite. This study investigated some reproductive and biochemical parameters in the nervous (CNS) and ovotestis (OT) tissues of Biomphalaria alexandrina during the course of Schistosoma mansoni infection. Antioxidant and oxidative stress parameters including catalase (CAT), nitric oxide (NO) and lipid peroxidation (MDA) were measured. Levels of steroid hormones, including testosterone, progesterone and estradiol, were also assessed. Finally, flow cytometry was used to compare measures of apoptosis between control snails and those shedding cercariae by examining mitochondrial membrane potential with the stain 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimi-dazolylcarbocyanine iodide (JC-1) and poly(ADP-ribose) polymerase (PARP). Infection with S. mansoni caused a 47.7% reduction in the net reproductive rate (Ro) of B. alexandrina. CAT activity was increased in the CNS at 21 days post infection (dpi) but by 28 dpi it was reduced below control values. Also, CAT activity increased significantly in the OT at 14, 21 and 28 dpi. In CNS tissues, NO levels were reduced at 7 dpi, increased at 14 and 21 dpi, and reduced again at 28 dpi. The overall level of lipid peroxidation gradually increased during the course of infection to reach its highest levels at 28 dpi. Steroid hormone measurements showed that concentrations of testosterone and estradiol were reduced in the CNS tissues at 28 dpi, while those of progesterone were slightly increased in the CNS and OT tissues. The percentage of cells that positively stained with JC-1was significantly increased in CNS and OT tissues of infected snails while the percentage of cells positively stained with PARP was decreased compared to controls. Together, these findings indicate that infection initiates diverse biochemical and hormonal changes leading to loss of cells responsible for egg laying and reproduction in B. alexandrina.

Reporte de Pseudosuccinea columella infectados con Fasciola hepatica en Sierra de los Cuchumatanes, Guatemala

Objetivo. Identificar la infección natural de caracoles de agua dulce con Fasciola hepatica en una localidad del altiplano de Guatemala. Materiales y métodos. Se colectaron caracoles de agua dulce en una aldea endémica de fascioliasis, en la localidad de Paquix, en el departamento de Huehuetenango, ubicado a ~3.300 msnm. La identificación de la especie de caracol se basó en las características morfológicas observadas por estereoscopio usando una clave de identificación. La búsqueda de fases del trematodo se realizó mediante la inspección visual externa con fuente de luz y la disección e inspección visual dentro del molusco bajo estereoscopio y microscopio. Resultados. 260 caracoles fueron encontrados e identificados como Pseudosuccinea columella. Se examinaron los especímenes colectados y se encontraron dos caracoles infectados de forma natural con fases larvarias de F. hepatica. Conclusiones. Este es el primer reporte de este hospedero intermediario portando formas de F. hepatica en Guatemala. Es necesario aumentar los reportes de este parásito y de sus interacciones ecológicas en otras áreas no estudiadas de Guatemala y Centro América, debido al riesgo latente de infección para poblaciones de animales herbívoros y humanos.

Molecular diversity of Bulinus species in Madziwa area, Shamva district in Zimbabwe: implications for urogenital schistosomiasis transmission

BackgroundBulinus species are freshwater snails that transmit the parasitic trematode Schistosoma haematobium. Despite their importance, the diversity of these intermediate host snails and their evolutionary history is still unclear in Zimbabwe. Bulinus globosus and B. truncatus collected from a urogenital schistosomiasis endemic region in the Madziwa area of Zimbabwe were characterized using molecular methods.MethodsMalacological survey sites were mapped and snails were collected from water contact sites in four communities in the Madziwa area, Shamva district for a period of one year, at three-month intervals. Schistosoma haematobium infections in snails were determined by cercarial shedding and the partial mitochondrial cytochrome c oxidase subunit 1 gene (cox1) was used to investigate the phylogeny and genetic variability of the Bulinus spp. collected.ResultsAmong the 1570 Bulinus spp. snails collected, 30 (1.9%) B. globosus were shedding morphologically identified schistosomes. None of the B. truncatus snails were shedding. The mitochondrial cox1 data from 166 and 16 samples for B. globosus and B. truncatus, respectively, showed genetically diverse populations within the two species. Twelve cox1 haplotypes were found from the 166 B. globosus samples and three from the 16 B. truncatus samples with phylogenetic analysis showing that the haplotypes fall into well-supported clusters within their species groups. Both B. truncatus and B. globosus clustered into two distinct lineages. Overall, significant negative values for both Tajima’s D statistic and the Fu’s Fs statistic were observed for B. globosus and B. truncatus.ConclusionsThe study provided new insights into the levels of genetic diversity within B. globosus and additional information on B. truncatus collected from a small geographical area in Zimbabwe. Low prevalence levels of infection observed in the snails may reflect the low transmission level of urogenital schistosomiasis in the area. Our results contribute towards the understanding of the distribution and population genetic structure of Bulinus spp. supporting the mapping of the transmission or risk of transmission of urogenital schistosomiasis, particularly in Zimbabwe.

Prevalence of cercarial infections in freshwater snails and morphological and molecular identification and phylogenetic trends of trematodes

Objective: To investigate the prevalence of cercarial infections in freshwater snails from several water sources in Nakhon Nayok, Nonthaburi, and Pathum Thani provinces of Central Thailand, and to reconstruct a phylogenetic tree for improved understanding of the relationships in the cercarial stage. Methods: The snail specimens were collected from 34 total sampling sites and investigated for cercarial infections using the crushing method. The cercarial specimens were classified and used for the phylogenetic tree analysis using the Internal Transcribed Spacer 2 (ITS2). Results: A total of 1 921 snail specimens were classified into five families and seven species. The results showed that four snail species were identified as intermediate hosts of the larval stages of trematodes, with an overall prevalence of infection of 2.45% (47/1 921). The infected snail specimens included five groups of the cercarial type: cercariaeum cercariae, echinostome cercaria, megalurous cercaria, parapleurolophocercous cercaria, and xiphidiocercariae. This is particularly true of xiphidiocercariae, which was found to be the dominant type among cercarial infections in bithyniid snails by approximately 38.00%. With regard to molecular identification, the phylogenetic tree was reconstructed using the neighbor-joining method with 10 000 bootstraps and separated the trematodes into three clades: Echinostomatoidea, Microphalloidea and Opisthorchioidea. Conclusions: The study reveals a high prevalence of cercarial infection for each cercarial type and maturation into a definite trematode genus and delineates morphological characteristics and evolutionary trends among each larval trematode in Nakhon Nayok, Nonthaburi and Pathum Thani provinces. In addition, the ITS2 sequence data of cercariae could be used to examine classification of these species at the family level.

Molecular detection of prepatent Schistosoma mansoni infection in Biomphalaria glabrata snail vectors.

ABSTRACTApproximately 240 million people worldwide are infected by Schistosoma. In Brazil, one of the main intermediate hosts of this parasite is Biomphalaria glabrata snails. The early detection of larval stages in intermediate hosts is an important challenge to public health, but it also represents an opportunity as a new alternative to indicate earlier natural infections before cercariae differentiation and emergence. In this context, we demonstrated that PCR amplification of a 28S gene fragment from the parasite does demonstrate S. mansoni infection in snails 14 days post infection. This conventional polymerase chain reaction amplified clear bands and was able to detect parasitic infection in the intermediate host B. glabrata under experimental conditions. However, we reinforce that this approach requires deeper investigations and further comparisons to confirm its specificity and sensitivity in earlier time points after miracidia infection. This approach has relevant potential as an effective molecular-based strategy for the monitoring of schistosomiasis transmission.

A Procedure for Analyzing the Proteomic Proteomics Profile of Schistosoma mansoni Cercariae.

Schistosomiasis is one of the most important helminthic parasitic infections in the world, with over 700million people at risk of infection. Species of Schistosoma have a complex life cycle involving the infection of freshwater snails before infecting their mammalian definitive host. Taking about 130,000 lives per annum, S. mansoni is the major cause of intestinal schistosomiasis worldwide. Within Biomphalaria glabrata snails, asexual replication of the parasite gives rise to cercariae larvae. Cercariae actively penetrate the host's skin to complete their life cycle and eventually transform into adult worms. If left untreated, intestinal schistosomiasis can lead to peripheral destruction of the portal vein system, gastric hemorrhage from esophageal varices, as well as hepatic failure. Mass spectrometry (MS) is the method of choice for proteomics analysis. The bottom-up proteomics approach-also known as "shotgun proteomics"-typically includes a protein extraction and solubilization step followed by proteolytic digestion and tandem MS (MS/MS) analysis. Proteins are later identified by peptide de novo sequencing upon MS and MS/MS spectra of digest peptides. In this chapter, we introduce an analytical workflow for proteome profiling of S. mansoni cercariae using bottom-up proteomics. The cercariae were isolated and lysed. Proteins were then extracted, enzymatically digested, and subjected to liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Proteins were identified using MaxQuant software. Cercariae are the first life stage of the parasite S. mansoni which humans encounter, and conducting proteomic analysis on this life cycle stage can shed light on possible drug or vaccine candidates to help disable the parasite's ability to infect or arm the immune system for parasite clearance.

Evaluation of changes in the carbohydrate metabolism of Biomphalaria glabrata Say, 1818 exposed to experimental coinfection by Angiostrongylus cantonensis (Nematoda) and Echinostoma paraensei (Trematoda)

The interaction between intermediate snail hosts and helminths can cause metabolic changes in the former. The snails use their reserves for maintenance of their vital processes, by activating the internal defense system and repairing tissue damage, while also supplying necessary energy for the parasites’ development. Our aims were to evaluate the lactate dehydrogenase activity and the glucose concentration in the hemolymph of Biomphalaria glabrata experimentally coinfected by Angiostrongylus cantonensis and Echinostoma paraensei. Besides these aspects, the glycogen content in the digestive gland complex and cephalopedal mass along with histochemical changes in parasitized snails were analyzed. The snails were divided in group A (infected by 1200 L1 of A. cantonensis), group E (infected by 20 E. paraensei miracidia), group A + E (co-infected with A. cantonensis first and after a week by E. paraensei), group E + A (co-infected with E. paraensei first and then by A. cantonensis) and control group (not infected). During four weeks after exposure, samples were collected for biochemical and histochemical analyses. In the infected snails, glucose levels and glycogen content in the digestive gland complex and cephalopedal mass were significantly lower, in contrast with an increase of lactate dehydrogenase activity. These results indicate that the intense energy demand resulting from the presence of parasites causes the host snail to accelerate the anaerobic degradation of carbohydrates to obtain energy, in an attempt to maintain homeostasis. Both parasites were observed in histochemical analysis to cause tissue damages in the snails. So, although the snails were able to sustain the coinfection, several metabolic and tissue changes occurred, mainly in those infected with E. paraensei and then with A. cantonensis.

Transcriptional responses of Biomphalaria pfeifferi and Schistosoma mansonifollowing exposure to niclosamide, with evidence for a synergistic effect on snails following exposure to both stressors.

BackgroundSchistosomiasis is one of the world’s most common NTDs. Successful control operations often target snail vectors with the molluscicide niclosamide. Little is known about how niclosamide affects snails, including for Biomphalaria pfeifferi, the most important vector for Schistosoma mansoni in Africa. We used Illumina technology to explore how field-derived B. pfeifferi, either uninfected or harboring cercariae–producing S. mansoni sporocysts, respond to a sublethal treatment of niclosamide. This study afforded the opportunity to determine if snails respond differently to biotic or abiotic stressors, and if they reserve unique responses for when presented with both stressors in combination. We also examined how sporocysts respond when their snail host is treated with niclosamide.Principal findingsCercariae-producing sporocysts within snails treated with niclosamide express ~68% of the genes in the S. mansoni genome, as compared to 66% expressed by intramolluscan stages of S. mansoni in snails not treated with niclosamide. Niclosamide does not disable sporocysts nor does it seem to provoke from them distinctive responses associated with detoxifying a xenobiotic. For uninfected B. pfeifferi, niclosamide treatment alone increases expression of several features not up-regulated in infected snails including particular cytochrome p450s and heat shock proteins, glutathione-S-transferases, antimicrobial factors like LBP/BPI and protease inhibitors, and also provokes strong down regulation of proteases. Exposure of infected snails to niclosamide resulted in numerous up-regulated responses associated with apoptosis along with down-regulated ribosomal and defense functions, indicative of a distinctive, compromised state not achieved with either stimulus alone.Conclusions/SignificanceThis study helps define the transcriptomic responses of an important and under-studied schistosome vector to S. mansoni sporocysts, to niclosamide, and to both in combination. It suggests the response of S. mansoni sporocysts to niclosamide is minimal and not reflective of a distinct repertoire of genes to handle xenobiotics while in the snail host. It also offers new insights for how niclosamide affects snails.

Endemic status of schistosomiasis in People's Republic of China in 2018

This report presented the endemic status of schistosomiasis in the People's Republic of China at a national level in 2018, and analyzed the data collected from the national schistosomiasis prevention and control system and 453 national schistosomiasis surveillance sites. Among the 12 provinces (municipality and autonomous region) endemic for schistosomiasis in China, 5 provinces (municipality and autonomous region), including Shanghai, Zhejiang, Fujian, Guangdong and Guangxi, continued to consolidate the achievements of schistosomiasis elimination, Sichuan Province achieved transmission interruption and 6 provinces of Yunnan, Jiangsu, Hubei, Anhui, Jiangxi and Hunan achieved transmission control by the end of 2018. There were 450 endemic counties (cities, districts) covering 260 million people, specifically including 28 456 endemic villages covering 70.059 7 million people at risk of infection. Among the 450 endemic counties (cities, districts), 58.44% (263/450), 27.56% (124/450) and 14.00% (63/450) reached the criteria of elimination, transmission interruption and transmission control, respectively. By the end of 2018, a total of 29 214 advanced schistosomiasis cases were documented in China. In 2018, a total of 11.127 6 million individuals received inquiry examinations and 2.062 9 million were positive; 7.191 4 million individuals received serological tests and 138.5 thousand of them were positive, 532.2 thousand individuals received stool examinations and 8 were positive in China. In 2018, snail survey was performed in 19 821 endemic villages and Oncomehania snails were found in 7 321 villages, accounting for 36.94% of all surveyed villages, with 3 newly detected villages with snails in China. Snail survey covered an area of 590 241.01 hm2 and 168 319.41 hm2 snail habitats were found, including emerging snail habitats of 61.28 hm2; however, no infected snails were identified. In 2018, a total of 646 823 bovines were raised in the schistosomiasis endemic areas of China, and 225 258 received serological examinations, with 2 638 positives detected, while 164 803 bovines received stool examinations, with 2 positives identified. In 2018, there were 90 388 patients with schistosomiasis receiving praziquantel chemotherapy, and expanded chemotherapy was given to 1 490 594 person-times; there were two bovines with schistosomiasis receiving praziquantel chemotherapy, and expanded chemotherapy was given to 352 577 bovine-times; chemical treatment was conducted in an area of 141 660.87 hm2, including an actual mollusciciding area of 75 308.26 hm2, and environmental improvements were performed in an area of 4 738.37 hm2 in China. Data from the 453 national schistosomiasis surveillance sites of China showed that the mean Schistosoma japonicum infection rates were 0.001 5% and zero in humans and bovines in 2018, respectively, and no infected snails were found. The results demonstrate that the endemic situation of schistosomiasis appears a tendency towards a continuous decline in China; however, there is still a risk of schistosomiasis transmission, and challenges remain in achieving the target set in the Thirteenth Five-Year National Plan for Schistosomiasis Control in 2020 in some regions.

Environmental determinants of distribution of freshwater snails and trematode infection in the Omo Gibe River Basin, southwest Ethiopia

BackgroundDetermination of infection rates of snail populations is one of the basic tools for epidemiological studies of snail borne diseases. In this study, we opted to determine the trematode infection of freshwater snails in the Omo-Gibe River Basin, southwest Ethiopia.MethodsWe collected snail samples from 130 observation sites in lakes, wetlands, rivers, reservoirs and irrigation canals surveyed during the dry season (March to May) in 2016. The snail samples were examined for trematode infections by cercarial shedding immediately after collection. Habitat conditions, water quality, human water contact practices and other human activities were assessed at each survey site. A redundancy analysis (RDA) was used to examine the relationship between cercarial infection and environmental variables. The statistical significance of eigenvalues and cercariae-environment correlations generated by the RDA were tested using Monte Carlo permutations at 499 permutations.ResultsA total of 3107 snails belonging to five species were collected. The most abundant species was Biomphalaria pfeifferi, representing 66% of the total collection. Overall, 109 (3.6%) of the snails were found infected with trematodes (cercariae). Biomphalaria pfeifferi was found to be the most highly infected, accounting 85% of all infected snails. A total of eight morphologically different types of cercariae were recorded, which included: Echinostoma cercariae, brevifurcate apharyngeate distome cercariae, amphistome cercariae, brevifurcate apharyngeate monostome cercariae, xiphidiocercariae, longifurcate pharyngeate distome cercariae, strigea cercariae and unidentified cercariae. Brevifurcate apharyngeate distome cercariae, and Echinostoma cercariae were the most abundant cercariae, accounting for 36 and 34% of all infection, respectively. The mean concentration of water conductivity and 5 days biological oxygen demand were higher in irrigation canals and lake sampling points. Human activities such as open field defecation, urination, livestock grazing, farming, and swimming were highly correlated with trematode infection.ConclusionsThe abundance, occurrence and infection rates of snail species were largely influenced by water physicochemical quality, sanitation and water contact behaviour of the inhabitants. Human activities, such as open field defecation and urination, livestock grazing, farming, and swimming were important predictors of the abundance of cercariae. Therefore, awareness creation should be implemented for proper containment of excreta (urine and faeces) and reducing human and animal contacts with surface waters to reduce snail-borne disease transmission.

The effect of trematode infection on the markers of oxidative stress in the offspring of the freshwater snail Lymnaea stagnalis.

Most invertebrate species exhibit immunological responses that can inactivate and eliminate penetrating parasites. Such immune responses in particular involve the formation of potentially toxic reactive oxygen species (ROS). We explored the immune capabilities of the first-generation (F1) offspring of naturally infected freshwater snails, Lymnaea stagnalis, in response to infection by trematode cercariae under laboratory conditions. The rates of ROS formation and peroxidase activity in the hemolymph of the F1 offspring of L. stagnalis parents infected by an asexual stage of trematodes were significantly higher than in F1 offspring of uninfected parents. Compared to offspring from uninfected parents, the growth rate of F1 snails from infected parents was higher, but survival was lower. After infection of F1 snails by trematode cercariae of Echinoparyphium aconiatum under laboratory conditions, the rate of ROS formation and peroxidase activity in the hemolymph of F1 offspring of uninfected parents increased compared to control snails. This pattern persisted throughout the entire 3-week observation period. In contrast, the rate of ROS formation in the hemolymph of F1 snails from infected parents after experimental infection by E. aconiatum cercariae did not differ from controls, and peroxidase activity even decreased. Thus, trematode parthenitae infection of parents could alter the immune response of their offspring.

First record of Bulimulus tenuissimus (Mollusca) as potential experimental intermediate host of Angiostrongylus cantonensis (Nematoda).

Snails are essential to complete the life cycle of the metastrongylid nematode Angiostrongylus cantonensis, the causative agent of infections in domestic and wild animals, mainly rodents, and also of neural angiostrongyliasis or eosinophilic meningitis in humans. There are many reports of mollusks that can act as intermediate hosts of this parasite, especially freshwater snails and the African giant Achatina fulica. The terrestrial gastropod Bulimulus tenuissimus is widely distributed in Brazil and other species of the same genus occur in Brazil and other countries, overlapping regions in which there are reports of the occurrence of A. cantonensis and angiostrongyliasis. In spite of this, there are no records in the literature of this species performing the role of intermediate host to A. cantonensis. The present study analyzed the experimental infection with first-stage larvae of A. cantonensis, under laboratory conditions, of B. tenuissimus, by using histology and electron microscopy techniques. Three weeks after exposure to L1 larvae, it was possible to recover L3 larvae in small numbers from the infected snails. Developing larvae were observed in the cephalopedal mass (foot), ovotestis, and mantle tissues, being located inside a granulomatous structure composed of hemocyte infiltration, but there was no calcium or collagen deposition in these structures in significant amounts. In the third week post exposure, it was possible observe a sheath around the developing larvae. The infected snails presented reduction in the fibrous muscular tissue in the foot region, loss of the acinar organization in the digestive gland, with increase of amorphous material inside the acini and loss of epithelial pattern of nuclear organization in the acinar cells. However, the ovotestis seemed unaffected by the infection, since there was a large number of developing oocytes and spermatozoa in different stages of formation. The digestion of infected snails allows us the third-stage recovery rate of 17.25%, at 14 days post exposure to the L1. These L3 recovered from B. tenuissimus were used to infect rats experimentally, and 43 days post infection first-stage (L1) larvae of A. cantonensis were recovered from fresh feces. The results presented constituted the first report of the role of B. tenuissimus as an experimental intermediate host to A. cantonensis and shed some light on a possible problem, since the overlapping distribution of B. tenuissimus and A. cantonensis in Brazil and other countries where different species of Bulimulus occur enables the establishment and maintenance of the life cycle of this parasite in nature, with wild rodents as reservoirs, acting as a source of infection to humans, causing neural angiostrongyliasis.

Association between Schistosoma mansoni Infection Rates in Humans and in Biomphalaria pfeifferi snails in Akwanga, Nasarawa State, Nigeria

Schistosomiasis is a neglected tropical disease of medical importance. Intestinal schistosomiasis caused by Schistosoma mansoni is less wide spread than urinary schistosomiasis in Nigeria. A study was carried out in Akwanga, Nasarawa State to determine the association between S. mansoni infection rates (prevalence) in humans and infection rates in Biomphalaria pfeifferi snails in Akwanga, Nasarawa State, Nigeria. The study was carried out in two communities: Gwanje community and MadaHills community in Akwanga. For infection rates in humans, four hundred (400) urine samples were tested for S. mansoni antigen using point of care circulating cathode antigen (POC-CCA) test kit. Infection rates in snails were determined by S. mansoni cercarial shedding by snails. Biomphalaria pfeifferi snails were more abundant and had significantly higher (p&lt;0.05) infection rates in dry season than rainy season in both Gwanje and MadaHills. There was a positive correlation between infection rates in humans in Gwanje and MadaHills (21.5%) and (14%) and infection rates in snails in Gwanje and MadaHills (13.9%) and (9.6%) respectively. Snails collected close to portions of the river that community residents earmarked for open defecation within freshwater bodies had significantly higher (p&lt;0.05) infection rates (15.8%) than snails collected from across river banks, (7.1%) and snail infection rates in areas designated for fetching water for drinking and domestic use was (12.7%) . Health education, improved sanitation practices and annual chemotherapy with praziquantel could help interrupt disease transmission and bring about schistosomiasis control in both Gwanje and MadaHills communities.