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Objective To investigating the microbial communities and physicochemical properties of soil and distribution of Oncomelania hupensis snails in marshlands along the Yangtze River basin at different types of land use, and to examine the effects of soil microorganisms and physicochemical properties on snail distribution, so as to provide insights into snail control and schistosomiasis prevention in marshland along the Yangtze River basin. Methods Marshlands with four types of land use were selected along the Yangtze River basin on April 2021, including poplar forest-crops integrated planting, reed areas, agricultural cultivation lands and ditches. The distribution of snails and physicochemical properties of soil were investigated in marshlands with different types of land use, and the V3 to V4 regions of the bacterial 16S ribosomal RNA (16S rRNA) gene, fungal internal transcribed spacer-1 (ITS1) gene and algal ribulose-bisphosphate carboxylase (rbcL) gene in soils were subjected to high-throughput sequencing. The occurrence of frames with living snails and density of living snails were compared in marshland with different types of land use. The associations of soil microorganisms and physicochemical properties with the density of living snails were examined using Pearson correlation analysis, and the contributions of soil microorganisms and physicochemical properties to the density of living snails were evaluated using variance partitioning analysis. Results In marshlands with four types of land use, the greatest occurrence of frames with living snails [(4.94 ± 2.14)%] and density of living snails [(0.070 ± 0.026) snails/0.1 m2] were seen in ditches, and the lowest were found in [(1.23 ± 1.23)%] agricultural cultivation lands [(0.016 ± 0.019) snails/0.1 m2]. A total of 2 phyla, 5 classes, 8 orders, 9 families and 11 genera of algae were detected in soils at four types of land use, with Chlorophyta as the dominant phylum and Pseudoneochloris as the dominant genus. A total of 44 phyla, 134 classes, 281 orders, 338 families and 516 genera of bacteria were detected in soils at four types of land use, with Proteobacteria and Acidobacteriota as the dominant phyla and uncultured Acidobacterium, MND1, Mitrospira, Haliangium and Sphingomonas as dominant genera. A total of 11 phyla, 41 classes, 108 orders, 223 families and 408 genera of fungi were detected in soils at four types of land use, with phyla Ascomycota, Basidiomycota and Mortierellomycota presenting high relative abundances and genera Cladorrhinum, Mortierella and Humicola presenting high relative abundances. Pearson correlation analysis revealed that the density of living snails correlated negatively with the relative abundance of Proteobacteria (r = −0.965, P < 0.05) and soil electronic conductivity (r = −0.962, P < 0.05) and positively with soil moisture (r = 0.951, P < 0.05). Variance partitioning analysis demonstrated that the physicochemical properties and microorganisms of soil contributed 69% and 10% to the density of living snails, respectively. Conclusion The diversity of microbial communities varies in soils at different types of land use in marshland along the Yangtze River basin, and the physicochemical properties and microorganisms of soils may affect the distribution of O. hupensis snails.
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Objective To analyze the trends in Oncomelania hupensis distribution in Wuhan City, Hubei Province from 2003 to 2022, so as to provide insights into precision schistosomiasis control. Methods Data pertaining to O. hupensis snail survey in Wuhan City from 2003 to 2022 were collected. The trends in the proportion of areas with snail habitats, actual area with snail habitats, mean density of living snails and prevalence of Schistosoma japonicum infection in snails were evaluated in schistosomiasis-endemic areas of Wuhan City from 2003 to 2022 with the slope of trend curve (β), annual percent change (APC) and average annual percent change (AAPC) using a Joinpoint regression model. Results During the period from 2003 through 2022, there were two turning points for the proportion of areas with snail habitats in Wuhan City in 2005 and 2015, with a rise during the period from 2003 to 2005 (β1 = 5.93, t = 1.280, P > 0.05), a decline from 2005 to 2015 (β2 = −0.88, t = −2.074, P > 0.05) and a rise from 2015 to 2022 (β3 = 1.46, t = −2.356, P < 0.05). During the period from 2003 through 2022, there were two turning points for the proportion of areas with snail habitats in islet endemic areas of Wuhan City in 2006 and 2015, with no significant differences in the trends from 2003 to 2006 (β1 = 4.64, t = 1.888, P > 0.05) or from 2006 to 2015 (β2 = −1.45, t = −2.143, P > 0.05), and with a tendency towards a rise from 2015 to 2022 (β3 = 2.04, t = −3.100, P < 0.05). During the period from 2003 through 2022, there were two turning points for the proportion of areas with snail habitats in inner embankment endemic areas of Wuhan City in 2012 and 2020, with a tendency towards a decline from 2003 to 2012 (β1 = −0.39, t = −4.608, P < 0.05) and with no significant differences in the trends from 2012 to 2020 (β2 = 0.03, t = 0.245, P > 0.05) and from 2020 to 2022 (β3 = 1.38, t = 1.479, P > 0.05). During the period from 2003 to 2022, the actual area with snail habitats all appeared a tendency towards a decline in Wuhan City, and in islet and inner embankment endemic areas of Wuhan City from 2003 to 2022 (AAPC = −2.39%, −5.75% and −2.35%, all P values < 0.05). The mean density of living snails reduced from 0.087 snails/0.1 m2 in 2003 to 0.027 snails/0.1 m2 in 2022 in Wuhan City, with a significant difference in the tendency towards the decline (APC = AAPC = −11.47%, P < 0.05). The annual mean decline rate of the mean density of living snails was 17.36% in outside embankment endemic areas of Wuhan City from 2003 to 2022 (APC = AAPC = −17.36%, P < 0.05), and there was no significant difference in the trends in the mean density of living snails in islet endemic areas of Wuhan City from 2003 to 2022 (APC = AAPC = −0.97%, P > 0.05). In addition, the prevalence of S. japonicum infection in snails appeared a tendency towards a decline in Wuhan City from 2003 to 2022 (APC = AAPC = −12.45%, P < 0.05). Conclusions The proportion of areas with snail habitats, actual area with snail habitats, mean density of living snails and prevalence of S. japonicum infection in snails all appeared a tendency towards a decline in Wuhan City from 2003 to 2022. Intensified snail control, modification of snail habitats, shrinking of areas with snails and implementation of grazing prohibition in snail-infested settings are required, in order to facilitate the progress towards schistosomiasis elimination in Wuhan City.
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Objective To investigate the changes in distribution of Oncomelania hupensis snails in forestlands in Songjiang District, Shanghai Municipality from 2009 to 2023, so as to provide insights into formulation of O. hupensis snail surveillance programs. Methods The reports on O. hupensis snail surveillance in Songjiang District, Shanghai Municipality from 2009 to 2023 were collected, and the snail surveillance data in forestlands were extracted. The trends in the proportion of areas with snails in forestlands in total areas with snails, occurrence of frames with living snails and density of living snails were evaluated using a Joinpoint regression model in Songjiang District from 2009 to 2023, and the annual percent change (APC) and average annual percent change (AAPC). Results A total of 40 sites with snails were found in forestlands in 14 administrative villages of 4 townships, Songjiang District, Shanghai Municipality from 2009 to 2023. A total of 39 065 frames were surveyed for snails in settings covering an area of 609 600 m2, and there were 6 084 frames with snails, covering 151 250 m2 snail habitats. A total of 22 210 snails were captured, with the highest density of 260.00 snails/0.1 m2, and 6 262 snails were dissected, with no Schistosoma japonicum infection identified in snails. The proportion of areas with snails in forestlands in total areas with snails appeared a tendency towards a rise in forestlands in Songjiang District, Shanghai Municipality from 2009 to 2023 (APC = AAPC = 24.9%, P > 0.05); however, there were no turning points in the trend curve, with the highest proportion seen in 2009 (53.81%), the lowest in 2011 and 2023 (both 0) and a mean proportion of 24.81%. The occurrence of frames with living snails appeared a tendency towards a rise from 2009 to 2023 (APC = AAPC = 41.5%, P > 0.05); however, there were no turning points in the trend curve, with the highest occurrence in 2009 (53.81%), the lowest in 2011 and 2013 (both 0), and the mean occurrence of 15.57%. In addition, the density of living snails appeared a tendency towards a rise from 2009 to 2023 (APC = AAPC = 55.0%, P > 0.05); however, there were no turning points in the trend curve, with the highest density in 2023 (0.96 snails/0.1 m2), the lowest in 2011 and 2013 (both 0), and a mean density of 0.57 snails/0.1 m2. Conclusions The difficulty in O. hupensis snail control and risk of imported snails appeared a tendency towards a rise in forestlands in Songjiang District, Shanghai Municipality over years from 2009 to 2023. Supervision and assessment prior to seedling transplantation and intensified surveillance post-transplantation are recommended to reduce the risk of O. hupensis snail importation and spread.
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Objective To examine the effect of ground cage use on Oncomelania hupensis spread, so as to provide insights into precision snail control. Methods Twenty ground cages that were frequently used to capture rice field eels were purchased, including 11 packaging tape-made cages, 7 plastic cages and 2 nylon rope-made cages. The eel-capturing activity was mimicked, and 20 ground cages were assigned in settings with relatively high (1.00 snail/0.1 m2 and higher) and low snail densities (< 1.00 snail/0.1 m2) in Xindai Township, Pinghu City, Zhejiang Province during the period from 15 : 00 to 8 : 00 of the following day on April 13, 26 and 28. The numbers of snails carried by different types of ground cages were compared in settings with different types of snail densities using the rank-sum test. Results A total of 11 cage-times were assigned in settings with a high snail density, and a total of 77 snails were captured, with a mean number of 7 snails in each cage-time and 2.15 snails in 0.1 m2 ground cage. The mean numbers of snails carried by packaging tape-made and plastic cages were 2.47 snails/0.1 m2 cage and 0.37 snails/0.1 m2 cage, respectively. A total of 24 cage-times were assigned in settings with a low snail density, and a total of 8 snails were captured, with a mean number of 0.33 snails in each cage-time and 0.09 snails in 0.1 m2 ground cage. The mean numbers of snails carried by packaging tape-made cages were 0.12 snails/0.1 m2 cage; however, no snails were carried by plastic or nylon rope-made cages. The number of snails carried by ground cages was higher in settings with a high snail density than in settings with a low snail density (Z = −4.019, P < 0.01), and the number of snails carried by packaging tape-made cages was higher in settings with a high snail density than in settings with a low snail density (Z = −4.086, P < 0.01). No significant differences were found in the numbers of snails carried by different types of ground cages. Conclusion The use of ground cage in snail habitats is a contributor to snail spread.
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ObjectiveTo genotype Oncomelania hupensis， based on microsatellites， in different snail-bearing environments in Jiaxing City， Zhejiang Province， for population genetics analysis in order to explore the reasons and influencing factors for the existence or proliferation of snails and to provide scientific basis for effective monitoring and control of snails. MethodsA total of 90 snail samples from three populations were collected in Yaobang Village （YB） and Sanxing Village （SX） in Pinghu City， and Yunhe Farm （YH） in Xiuzhou District， all were selected for snail checking in key snail habitats of Jiaxing City in 2022. DNA of the snails was genotyped and analyzed for population genetics using nine microsatellite loci. ResultsA total of 84 alleles were observed， and the mean number of alleles （Na） was 7.889， 5.667， and 3.778 for YB， SX， and YH respectively； the number of effective alleles （NeA） was 4.807， 3.329， and 2.294， respectively； and the coefficients of inbreeding （FIS） were 0.400， 0.377， and 0.493， respectively. Under the Infinite Allele Model （IAM）， the SX and YH might have a recent bottleneck. The NEstimator and LDNe software calculated effective population sizes （Ne） were above 31.9. AMOVA analysis showed that the variation of snails in the three populations mainly existed among individuals， accounting for 41.4% of the total variation. The value of the index of genetic differentiation between populations （FST） was 0.286， indicating a high degree of genetic differentiation. The results of the principal component analysis and phylogenetic tree were consistent， and the three populations were divided into two lineages， YB and SX were one lineage， and YH belonged to another independent lineage. Population history and dynamics analysis showed that the gene flow of the three populations was insufficient， population divergence history indicated that YH might have diverged from SX first， and YB was produced by the contact fusion of SX and YH. ConclusionThe genetic diversity of snail populations in Jiaxing City is generally low， and the snail populations are unstable， with a great degree of genetic differentiation and insufficient gene flow among populations. This study can provide a basis for evaluating the effectiveness of the control of the snail as well as monitoring the trend of the spread of the snail.
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Objective To investigate ecological isolation between Oncomelania hupensis snail populations in hilly regions and marshland and lake regions in Yuanjiang valley, Changde City, Hunan Province, and to unravel its underlying mechanisms. Methods Taoyuan County, Shimen County, Linli County and Lixian County in Changde City were selected as snail sampling sites in hilly regions, and Lixian County, Jinshi City, West Lake Administration District, Hanshou County and Dingcheng District were selected as snail sampling sites in marshland and lake areas. Cytochrome C oxidase 1 (cox 1) gene was amplified in snail samples and sequenced. The genetic sequences of O. hupensis snails were aligned using the software MEGA 11, and the haplotypes of O. hupensis snails were determined using the software DNASP 5.10.01. The phylogenetic tree was generated using Bayesian inference with the software MrBayes 3.2, and analysis of molecular variance (AMOVA) was performed to analyze the source of genetic divergence and estimate the genetic divergence index (FST) among snail populations with the software Arlequin 3.5.2.2. The genetic barrier among 11 O. hupensis snail populations was estimated using the Monmonier algorithm of adegenet toolkit in R package. The settings with “land in winter and water in summer” in the Yuanjian River section were divided into two categories according to the upstream and downstream, and the areas with “land in winter and water in summer” in the upstream and downstream were transformed into raster data, and then loaded into the software Fragstats 4 for analysis of landscape indicators. The trends in changes of digital elevation were extracted from the Yuanjiang River section based on the digital elevation model, and made three-dimensional visualization using the R package. Results The mitochondrial cox 1 gene were amplified in 165 O. hupensis snais from 11 sampling sites and sequenced, and a total of 152 valid gene sequences were obtained, with 46 haplotypes or 9 populations determined. No haplotype was shared in snails between Taoyuan County and Dingcheng District and Hanshou County along the downstream of the Yuanjiang River. The total area of settings with “land in winter and water in summer” was 617.66 hm2 in the upsteram of the Yuanjiang River, which consisted of 473 patches, with each patch measuring 1.31 hm2, the largest area index of 0.735 2, the landscape division index of 0.999 9, and the landscape shape index of 45.293 7. The total area of settings with “land in winter and water in summer” was 9 956.92 hm2 in the downstream of the Yuanjiang River, which consisted of 771 patches, with each patch measuring 12.91 hm2, the largest area index of 97.839 9, the landscape division index of 0.042 7, and the landscape shape index of 7.249 6. The area of settings with “land in winter and water in summer” was much larger in the downstream than that in the upstream of the Yuanjiang River, and the stronger landscape connectivity and non-remarkable alteration of riverbed elevation provided suitable habitats for snail breeding. Conclusion The hydrological and environmental characteristics of the upstream of the Yuanjiang River restrain the breeding and spread of O. hupensis, resulting in ecological isolation between Oncomelania hupensis in Taoyuan County and those in the downstream of Yuanjiang River.
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Objective:To explore the spatial and temporal distribution patterns of emerging snail-infested sites in different environmental types in Yunnan Province.Methods:The data of snail-infested sites in Yunnan Province from 1950 to 2014 (from Yunnan Institute for Endemic Diseases Control and Prevention), were collected and sorted out, a spatial and temporal database on the distribution of emerging snail-infested sites were established, and the changes in the spatial and temporal distribution of emerging snail-infested sites in different environments types (ditches, tangerines, paddy fields, dry land, beaches and other environments) were studied by using spatial autocorrelation analysis and scanning statistics analysis.Results:From 1950 to 2014, the annual number of emerging snail-infested sites in Yunnan Province reached a peak (1 730) in 1955 and then showed a fluctuating downward trend. From 1993 to 2014, the number of emerging snail-infested sites remained below 100, and increased to 160 and 131, respectively, in 2004 and 2013. The longest mean duration of 43.85 years was recorded for the beaches environment for emerging snail-infested sites, followed by the paddy fields environment with a mean duration of 37.01 years, and the shortest mean duration of 20.44 years for the tangerines environment. Spatial autocorrelation analysis showed that there was a positive spatial correlation between the duration of emerging snail-infested sites of different environmental types (global Moran's I ranged from 0.43 to 0.64, P < 0.05). Scanning statistics analysis showed that emerging snail-infested sites of different environmental types had spatial and temporal aggregation ( P < 0.001), with 3- 6 clusters of statistically significant aggregation detected respectively. Conclusion:The emerging snail-infested sites in different environments types in Yunnan Province have spatial and temporal aggregation, and it is necessary to strengthen monitoring and prevention and control of the aggregation areas of different environment types to prevent further spread of the snail.
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Objective@#To compare the effectiveness before and after the adjustment of schistosomiasis control strategies in Nanjing City, so as to provide the evidence for improving schistosomiasis control interventions.@*Methods@#The prevalence of Schistosomasis japonicum infections in humans, livestock, Oncomelania hupensis and sentinel mice was collected in Nanjing City from 1993 to 2018, and the prevalence of S. japonicum infections in humans, livestock, sentinel mice and O. hupensis, and the areas of snail habitats, areas of infected snail habitats and snail control areas were compared before (1993-2004) and after (2005-2018) the adjustment of schistosomiasis control strategies to evaluate the effectiveness.@*Results@#The prevalence of S. japonicum infections in humans, livestock, O. hupensis and sentinel mice was 0.77% and 0.02% (χ2=6 430.634, P<0.001), 0.46% and 0.01% (χ2=344.401, P<0.001), 0.19% and 0.11% (χ2=239.685, P<0.001), and 34.35% and 1.56% (χ2=1 856.286, P<0.001) in Nanjing City before and after the adjustment of schistosomiasis control strategies, respectively. The median areas (interquartile range) of snail habitats, infected snail habitats and snail control were 4 175.37 (1 301.65) and 2 366.44 (885.27) hm2 (Z=-3.755, P<0.001), 870.49 (1 001.75) and 0 (158.89) hm2 (Z=-3.654, P<0.001) and 1 383.23 (793.57) and 5 031.94 (629.11) hm2 (Z=-4.320, P<0.001) in Nanjing City before and after the adjustment of schistosomiasis control strategies, respectively.@*Conclusions@#After the adjustment of schistosomiasis control strategies, remarkable effects on schistosomiasis control has achieved in Nanjing City, where the transmission of schistosomiasis was interrupted. Nevertheless, the strategy requires to be continued and improved to move towards elimination of schistosomiasis in Nanjing City.
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Objective To screen the targets of traditional Chinese medicine-derived potential plant molluscicides based on network pharmacology and explore the mechanisms of molluscicidal actions. Methods The traditional Chinese medicines with molluscicidal actions were screened based on retrospective literature reviews, and their molluscicidal efficiency was summarized. The active ingredients and potential targets of traditional Chinese medicines were captured from the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform, Unified Protein Database and literature mining using network pharmacology. The drug-active ingredient-target network was created using the software Cytoscape 3.7.2, and the key targets were subjected to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis using the Metascape software. Results A total of 27 types of snail control drugs derived from traditional Chinese medicines were screened from publications and classified into 14 categories. Network pharmacology identified 190 active ingredients, and the active ingredients with a high degree in the drug-active ingredient-target network included quercetin, linoleyl acetate, luteolin, beta-carotene, (24S)-ethylcholesta-5,22,25-trans-3beta-ol, fumarine and arctiin, with 181 corresponding potential targets screened. KEGG pathway enrichment analysis revealed that these targets were mainly located in 16 pathways, including the neuroactive ligand-receptor interactions, regulation of adipocyte lipolysis and adrenergic signal in myocardial cells. Conclusions This study preliminarily demonstrates the multi-ingredient, multi-target and multi-pathway mechanisms of action of 27 molluscicides. The screened key ingredient may provide the basis for isolation, purification and pharmacological studies of molluscicides, and the screened key targets and key pathways may facilitate the illustration of mechanisms of actions of traditional Chinese medicine-derived molluscicides and development of novel green molluscicides.
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Oncomelania hupensis is the only intermediate host of Schistosoma japonicum, and O. hupensis control is an important measure for schistosomiasis control. With the progress of national schistosomiasis control program, the prevalence of schistosomiasis is low in China; however, there are still multiple challenges for O. hupensis breeding and schistosomiasis transmission risk. Considering the target of the national schistosomiasis elimination program and environmental protection in the new era, the introduction of precision identification, precision interventions and precision assessment into O. hupensis control may facilitate the progress towards elimination of schistosomiasis in China.
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Objective To investigate the morphological variation of Oncomelania hupensis shells in Yunnan Province, so as to provide insights into the understanding of O. hupensis genetic evolution and control. Methods According to the O. hupensis density, geographical location, altitude, water system and environmental type, 12 administrative villages were sampled from 10 schistosomiasis-endemic counties (districts) in 3 prefectures (cities) of Yunnan Province as snail collection sites. From December 2021 to January 2022, about 200 snails were collected from each collection site, among which thirty adult snails (6 to 7 spirals) were randomly selected from each site, and the 11 morphological indexes of snail shells were measured and subjected to cluster analysis and principal component analysis. Results Of O. hupensis snails from 12 localities of Yunnan Province, the longest shell (7.33 mm) was detected in snails from Yongle Village, Eryuan County, with the shortest (4.68 mm) in Dongyuan Village, Gucheng District, and the largest angle of apex (59.47°) was measured in snails from Caizhuang Village, Midu County, with the smallest (41.40°) in Qiandian Village, Eryuan County. The mean coefficient of variation was 9.075% among O. hupensis snails from 12 localities of Yunnan Province, with the largest coefficient of variation seen in the thickness of the labra brim (29.809%). Among O. hupensis snails from 12 localities of Yunnan Province, the mean Euclidean distance was 2.26, with the shortest Euclidean distance seen between O. hupensis snails from Qiandian Village of Eryuan County and Wuxing Village of Dali City (0.26), and the largest found between O. hupensis snails from Caizhuang Village of Midu County and Cangling Village of Chuxiong County (8.17). Cluster analysis and principal component analysis classified O. hupensis snails from 12 localities of Yunnan Province into three categories, including the O. hupensis snail samples from Caizhuang Village of Midu County, O. hupensis snail samples from Cangling Village of Chuxiong County, and O. hupensis snail samples from Qiandian Village of Eryuan County, Wuxing Village of Dali City, Yangwu Village of Yongsheng County, Xiaoqiao Village of Xiangyun County, Yongle Village of Eryuan County, Xiaocen Village of Dali City, Anding Village of Nanjian County, Dongyuan Village of Gucheng District, Lianyi Village of Heqing County, and Dianzhong Village of Weishan County. The variations in these three categories of snail samples were mainly measured in the principal component 2 related to the angle of apex and the thickness of the labra brim. Conclusions The variations in the Euclidean distance and morphological features of shells of O. hupensis from 12 localities of Yunnan Province gradually rise with the decrease in the latitude of the collection sites. The angle of apex is an indicator for the growth of O. hupensis whorl.
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Objective To establish a deep learning-based visual model for intelligent recognition of Oncomelania hupensis, the intermediate host of Schistosoma japonicum, and evaluate the effects of different training strategies for O. hupensis image recognition. Methods A total of 2 614 datasets of O. hupensis snails and 4 similar snails were generated through field sampling and internet capture, and were divided into training sets and test sets. An intelligent recognition model was created based on deep learning, and was trained and tested. The precision, sensitivity, specificity, accuracy, F1 score and Youden index were calculated. In addition, the receiver operating characteristic (ROC) curve of the model for snail recognition was plotted to evaluate the effects of “new learning”, “transfer learning” and “transfer learning + data enhancement” training strategies on the accuracy of the model for snail recognition. Results Under the “transfer learning + data enhancement” strategy, the precision, sensitivity, specificity, accuracy, Youden index and F1 score of the model were 90.10%, 91.00%, 97.50%, 96.20%, 88.50% and 90.51% for snail recognition, which were all higher than those under both “new learning” and “transfer learning” strategies. There were significant differences in the sensitivity, specificity and accuracy of the model for snail recognition under “new learning”, “transfer learning” and “transfer learning + data enhancement” training strategies (all P values < 0.001). In addition, the area under the ROC curve of the model was highest (0.94) under the “transfer learning + dataenhancement” training strategy. Conclusions This is the first visual model for intelligent recognition of O. hupensis based on deep learning, which shows a high accuracy for snail image recognition. The “transfer learning + data enhancement” training strategy is helpful to improve the accuracy of the model for snail recognition.
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Objective To evaluate the impact of water pollutants, water levels and meteorological factors on the Oncomelania hupensis density in Eastern Dongting Lake regions, so as to provide insights into schistosomiasis control. Methods O. hupensis snails were surveyed using a systematic sampling method in snail-infested marshlands in Eastern Dongting Lake regions from 2007 to 2014, and data pertaining to water pollutants, water levels and meteorological factors were collected. The duration of submergence and the date of the start of submergence were calculated. The snail density and its influencing factors were descriptively analyzed, and a linear mixed model was generated to examine the impacts of variables on the snail density. In addition, smooth curves were fitted to investigate the relationship between snail density and variables. Results The snail density appeared a fluctuation in Eastern Dongting Lake regions during the period from 2007 to 2014, with the highest density on October, 2010 (52.79 snails/0.1 m2) and the lowest density on January 2009 (2.15 snails/0.1 m2). Linear mixed-model analysis showed that permanganate index, total phosphorus and the date of the start of submergence affected the snail density (t = 6.386, −2.920 and −3.892, all P values < 0.01). Smooth curve analysis revealed that the associations of the snail density with the permanganate index and total phosphorus appeared an approximately quadratic curve. After the end of April, the earlier date of the start of submergence resulted in a higher snail density. Conclusion Permenganate index, total phosphorus and the date of the start of submergence affect the O. hupensis snail density in Eastern Dongting Lake regions.
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Objective To investigate the effectiveness and cost of 50% and 80% wettable powder of niclosamide ethanolamine salt (NESWP) and 26% metaldehyde and niclosamide suspension concentrate (MNSC) in hilly schistosomiasis-endemic regions, so as to provide insights into the selection of chemical molluscicides in hilly regions. Methods In September 2020, a wasteland in Guanshanqiao Village, Yanrui Township, Yushan County of Jiangxi Province was selected as the experimental region, which was sectioned into five blocks and defined as four experimental groups (A1, A2, B, C) and a blank control group (D). 80% NESWP were given at doses of 1 g/m2 and 1.5 g/m2 in groups A1 and A2 using the spraying method, 50% NESWP was given at a dose of 2 g/m2 in Group B using the spraying method, and 26% MNSC was at a dose of 4 g/m2 in Group C using the spraying method, while no chemical treatment was given in Group D. Snail survey was performed using a systematic sampling method before chemical treatment and 1, 3, 7 d and 15 d post-treatment to examine the molluscicidal effect, and all molluscicidal costs were estimated to calculate the cost of chemical treatment per 1 m2 and the cost of the reduction in the mean density of living snails per 1%. Results The highest mortality of snails was 78.95% and the lowest density of living snails was 0.2388 snails/0.1 m2 in the experimental groups within 7 d of chemical treatment, and the highest mortality of snails was 94.74% and the lowest density of living snails was 0.058 0 snails/0.1 m2 7 d post-treatment. There were no significant differences in the snail mortality among the A1, A2, B and C groups 1 (χ2 = 2.250, P > 0.05), 3 (χ2 = 1.779, P > 0.05) or 15 d post-treatment (χ2 = 2.286, P > 0.05), while a significant difference was detected in the snail mortality among the four groups 7 d post-treatment (χ2 = 7.990, P = 0.046). In addition, there were no significant differences in the snail mortality between A1 and A2 groups 1 (χ2 = 0.724, P > 0.05), 3 (χ2 = 0.584, P > 0.05), 7 (χ2 = 0.400, P > 0.05) or 15 d post-treatment (χ2 = 0.251, P > 0.05). The costs of chemical treatment per 1 m2 were 0.58, 0.60, 0.64 Yuan and 0.73 Yuan in groups A1, A2, B and C, and the costs of the mean density of living snail per 1% reduction were 19.29, 20.44, 21.68 Yuan and 23.53 Yuan in groups A1, A2, B and C, respectively. Conclusion 80% NESWP shows a high molluscicidal efficacy and low cost in hilly schistosomiasis-endemic regions.
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Objective To analyze the monitoring data of Oncomelania hupensis in the national schistosomiasis surveillance sites of China from 2015 to 2019, so as to understand the changes of Oncomelania snail status in the schistosomiasis-endemic areas of China and to provide the scientific evidence for Oncomelania snail control. Methods According to the requirements of National Scheme for Schistosomiasis Surveillance in China (2014 Edition), national schistosomiasis surveillance sites were assigned in all schistosomiasis-endemic counties (cities, districts) and the potential endemic counties (cities, districts) in the Three Gorges Reservoir areas, and Oncomelania snail status was monitored according to different epidemic types. In endemic areas, Oncomelania snail survey was performed by means of systematic sampling and environmental sampling, and the occurrence of frames with Oncomelania snails and the prevalence of Schistosoma japonicum infections in Oncomelania snails were calculated, while in potential endemic areas, the risk of imported Oncomelania snails and Oncomelania snails in floating debris were monitored. Results Oncomelania snail survey was performed covering an area of 116 834.16 hm2 in the national schistosomiasis surveillance of China from 2015 to 2019, with 35 007.62 hm2 Oncomelania snail habitats identified. A total of 6 908 292 frames were surveyed during the 5-year period, and there were 364 555 frames detected with Oncomelania snails, with a 5.28% mean occurrence of frames with Oncomelania snails. Among 997 508 living Oncomelania snails captured, no S. japonicum infections were detected, and loop-mediated isothermal amplification (LAMP) assay detected 18 positive mixed Oncomelania snail samples. During the period from 2015 to 2019, 147.20 hm2 emerging Oncomelania snail habitats were identified, with an overall tendency towards a rise seen in the proportion of emerging Oncomelania snail habitats in plain regions with waterway networks (0.12% to 92.00%), a tendency towards a rise followed by decline seen in marshland and lake regions (0 to 96.72%), and a large fluctuation in hilly regions (0 to 88.49%). A total of 831.10 hm2 re-emerging Oncomelania snail habitats were found in the national schistosomiasis surveillance sites of China from 2015 to 2019, with an overall tendency towards a rise seen in the proportion of re-emerging Oncomelania snail habitats in marshland and lake regions (16.05% to 79.66%), an overall tendency towards a decline seen in hilly regions (19.25% to 81.00%), and a minor fluctuation in plain regions with waterway networks (1.10% to 10.14%). During the 5-year period from 2015 to 2019, a total of 48 656 kg floating debris were captured in 4 surveillance sites in the Three Gorges Reservoir areas, and 2 204 snails were found, with no Oncomelania snails identified. Conclusions The areas of Oncomelania snail habitats tended to be stable in the national schistosomiasis surveillance sites of China during the period from 2015 to 2019, however, there was a gradual rise in the area of Oncomelania snail habitats year by year, and LAMP assay identified positive Oncomelania snail samples, suggesting Oncomelania snail control is far from optimistic in China.
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Objective To investigate the distribution characteristics of Oncomelania hupensis in Guangxi Zhuang Autonomous Region, so as to provide insights into the assessment of the risk of schistosomiasis transmission and the scientific formulation of the schistosomiasis surveillance strategy. Methods From 2015 to 2019, a total of 19 national schistosomiasis surveillance sites were assigned in Guangxi Zhuang Autonomous Region, including 4 fixed sites and 15 mobile sites. Snail survey was performed by means of systematic sampling in combination with environmental sampling, and the infection of Schistosoma japonicum was detected by the crushing method combined with loop-mediated isothermal amplification (LAMP) assay. Results From 2015 to 2019, snail habitats were detected at areas of 17 040 to 39 527 m2, including 6 214 m2 emerging snail habitats and 16 563 m2 re-emerging snail habitats. The overall mean density of living snails was 0.019 2 snails/0.1 m2 and the occurrence of frames with snails was 1.11% in the national schistosomiasis surveillance sites; however, no S. japonicum infection was identified in snails. The area of snail habitats increased by 121.46% in the national surveillance sites in 2019 as compared to that in 2015; however, 50.34% (Z = −0.422, P > 0.05) and 42.85% (χ2 = 130.41, P < 0.01) reductions were seen in the overall means density of living snails and the occurrence of frames with snails. All snail habitats were distributed in the 4 fixed surveillance sites, and were mainly found in ditches, paddy fields and dry lands, with weeds as the primary vegetation type. Conclusions There are still risk factors leading to re-emergent transmission of schistosomiasis in Guangxi Zhuang Autonomous Region, such as local snail spread, and the monitoring of schistosomiasis remains to be reinforced to further consolidate the achievements of schistosomiasis elimination in the region.
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Objective To assess the molluscicidal activity of the of Bacillus Y6 strain against Oncomelania hupensis in laboratory, and to preliminarily investigate its mechanisms of molluscicidal actions. Methods Biological identification of the Y6 strain was performed based on analysis of its morphological and physiochemical features and homology analysis of the 16S rDNA gene sequence. Bacillus Y6 suspensions were formulated at concentrations of 0.005, 0.010 g/mL and 0.015 g/mL, and the molluscicidal activity of Bacillus Y6 suspensions against O. hupensis was tested in laboratory using the immersion method. In addition, the Bacillus Y6 content and glycogen content were detected in O. hupensis following exposure to Bacillus Y6 suspensions to preliminarily explore the molluscicidal mechanism of the Bacillus Y6 strain against O. hupensis. Results The colony of the Bacillus Y6 strain appeared non-transparent milky white, and mycoderma was produced on the surface of the nutrient agar liquid medium. The Y6 stain was Gram positive and rod-shaped, and the endospore was located at the center of the Bacillus Y6 strain and appeared an achromatic, transparent and refractive body, which was encapsulated by the Y6 strain. The Y6 strain was positive for the lecithinase test, and the 16S rDNA gene sequence showed a 100% homology with those of multiple B. velezensisis strains, B. amyloliquefaciens and B. subtilis. The Y6 strain was therefore identified as B. velezensisis. Following immersion in the Bacillus Y6 suspensions at concentrations of 0.005, 0.010 g/mL and 0.015 g/mL for 24, 48 h and 72 h, the mortality rates of Oncomelania snails were 28.3%, 31.7% and 81.6%, 43.3%, 58.3% and 93.3%, and 63.3%, 78.3% and 98.3%, respectively. The molluscicidal activity of the Bacillus Y6 suspensions increased with the suspension concentration and duration of immersion. Microscopy and colony counting revealed the highest Y6 content in dead snails and the lowest in living snails following immersion in Bacillus Y6 suspensions, and the mean glycogen contents were (0.68 ± 0.06), (1.09 ± 0.16) μg/mg and (2.56 ± 0.32) μg/mg in the soft tissues of dead, dying and living snails following immersion in Bacillus Y6 suspensions (F = 59.519, P < 0.05), and the mean glycogen content was significantly higher in living snails than in dead (t = 14.073, P < 0.05) and dying snails (t = 10.027, P < 0.05), while the mean glycogen content was significantly higher in dying snails than in dead snails (t = 5.983, P < 0.05). Conclusion The B. velezensisis Y6 strain shows a high molluscicidal activity against O. hupensis snails, and its invasion may cause glycogen metabolism disorders, leading to snail death.
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Objective To evaluate the effectiveness of the integrated schistosomiasis control measures in Changzhou City from 2015 to 2020, so as to provide insights into the formulation of the strategy used to consolidate the schistosomiasis elimination achievements. Methods The annual schistosomiasis control working report and integrated schistosomiasis control data were collected in Changzhou City from 2015 to 2020, and the prevalence of Schistosoma japonicum infections in humans and livestock and snail status were analyzed to evaluate the effectiveness of the integrated schistosomiasis control measures. Results During the period from 2015 to 2020, a total of 112 061 person-time individuals received serological tests for S. japonicum infections in Changzhou City, and the sero-prevalence was 0.15% to 1.09% during the 6-year period, with a significant difference seen among years (χ2 = 288.11, P < 0.05). From 2015 to 2020, a total of 13 435 person-time individuals received stool examinations, with no egg-positives identified; among 5 840 herd-time livestock receiving schistosomiasis examinations, no positives were detected, while a 100% coverage of fencing livestock was seen each year. During the 6-year period, a total of 38.40 hm2 snail habitats were found, including 8.97 hm2 emerging snail habitats, and among the 2 344 snails dissected, no S. japonicum infection was found. Chemical treatment covered an area of 385.71 hm2, and environmental improvements covered an area of 200.39 hm2. The mean density of living snails was less than 0.1 snails/0.1 m2 in snail habitats found in Changzhou City each year from 2015 to 2020, and the coverage of harmless toilets was 100% in 2020. During the 6-year period, a total of 3.740 6 million person-time individuals were given schistosomiasis health education in Changzhou City. Conclusions Changzhou City is now at the post-elimination surveillance stage; however, there are still factors affecting schistosomiasis transmission. The schistosomiasis surveillance system remains to be improved to consolidate the schistosomiasis elimination achievements in Changzhou City.
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Before and after the construction of the South-to-North Water Diversion Project, a number of studies have been conducted to assess the possibility of the northward spread of Oncomelania snails and schistosomiasis caused by the construction of the project, the survival and reproduction of snails moved north of their natural distribution, and the transmission of schistosomiasis by the survival snails moved north of their natural distribution. The effect of the South-to-North Water Diversion Project on the transmission of schistosomiasis is restricted along the Jiangsu section of the eastern route project of the South-to-North Water Diversion Project, and the Water Transfer Project from the Yangtze River to Han River of the middle route project of the South-to-North Water Diversion Project. It has been demonstrated the water diversion pattern via the pump stations and the ecological conditions in the water transfusion channels of the South-to-North Water Diversion Project are unlikely to result in the northward spread of Oncomelania snails or schistosomiasis, and no snails or schistosomiasis spread was found during the surveillance before and after the operation of the eastern route project of the South-to-North Water Diversion Project, and the Water Transfer Project from the Yangtze River to Han River of the middle route project of the South-to-North Water Diversion Project. Nevertheless, sustainable surveillance of Oncomelania snails along the South-to-North Water Diversion Project will provide scientific support and safety guarantee for the construction and operation of the subsequent projects.
ABSTRACT
Objective To investigate the spatio-temporal distribution characteristics of Oncomelania hupensis snail habitats in three cities of Suzhou, Wuxi and Changzhou along the Taihu Lake region, so as to provide technical supports for establishing a sensitive and highly effective surveillance and forecast system for schistosomiasis. Methods Snail distribution data were collected from Suzhou, Wuxi and Changzhou cities from 1950 to 2018, and the changing trend for snail habitats were described over years. In addition, the clusters of snail habitats were detected using Kernel density analysis and SaTScan space-time scan analysis. Results The number of snail habitats appeared a single-peak distribution in Suzhou, Wuxi and Changzhou cities from 1950 to 2018, which peaked in 1970 and then declined rapidly. There were 62.68% of snail habitats eliminated within 10 years after identification, of which 38.24% were eliminated at the year of identification. Kernel density analysis and SaTScan space-time scan analysis revealed that high-density clusters of snail habitats were mainly distributed in Kunshan City, Wuzhong District and Xiangcheng District from 1970 to 1980, and in Yixing City in 1990; since then, the clusters gradually shrank, and overall appeared a move from northeast to west of Taihu Lake. A total of 4 new clusters were detected after 1970, as revealed by space-time scanning of snail habitats. In current snail habitats, emerging snail habitats are mainly identified in Huqiu District (Dongzhu Town), Wuzhong District (Guangfu Town), Taicang City (Shaxi Town) and Jintan District, and re-emerging snail habitats are scattered in 7 districts. Conclusions The distribution of snail habitats are spatio-temporal aggregation in Suzhou, Wuxi and Changzhou cities. The monitoring and prediction of emerging and re-emerging snail habitats are the key points in the future.