Hupensis Snails Research Articles

Prediction of trends for fine-scale spread of Oncomelania hupensis in Shanghai Municipality based on supervised machine learning models

To predict the trends for fine-scale spread of Oncomelania hupensis based on supervised machine learning models in Shanghai Municipality, so as to provide insights into precision O. hupensis snail control. Based on 2016 O. hupensis snail survey data in Shanghai Municipality and climatic, geographical, vegetation and socioeconomic data relating to O. hupensis snail distribution, seven supervised machine learning models were created to predict the risk of snail spread in Shanghai, including decision tree, random forest, generalized boosted model, support vector machine, naive Bayes, k-nearest neighbor and C5.0. The performance of seven models for predicting snail spread was evaluated with the area under the receiver operating characteristic curve (AUC), F1-score and accuracy, and optimal models were selected to identify the environmental variables affecting snail spread and predict the areas at risk of snail spread in Shanghai Municipality. Seven supervised machine learning models were successfully created to predict the risk of snail spread in Shanghai Municipality, and random forest (AUC = 0.901, F1-score = 0.840, ACC = 0.797) and generalized boosted model (AUC= 0.889, F1-score = 0.869, ACC = 0.835) showed higher predictive performance than other models. Random forest analysis showed that the three most important climatic variables contributing to snail spread in Shanghai included aridity (11.87%), ≥ 0 °C annual accumulated temperature (10.19%), moisture index (10.18%) and average annual precipitation (9.86%), the two most important vegetation variables included the vegetation index of the first quarter (8.30%) and vegetation index of the second quarter (7.69%). Snails were more likely to spread at aridity of < 0.87, ≥ 0 °C annual accumulated temperature of 5 550 to 5 675 °C, moisture index of > 39% and average annual precipitation of > 1 180 mm, and with the vegetation index of the first quarter of > 0.4 and the vegetation index of the first quarter of > 0.6. According to the water resource developments and township administrative maps, the areas at risk of snail spread were mainly predicted in 10 townships/subdistricts, covering the Xipian, Dongpian and Tainan sections of southern Shanghai. Supervised machine learning models are effective to predict the risk of fine-scale O. hupensis snail spread and identify the environmental determinants relating to snail spread. The areas at risk of O. hupensis snail spread are mainly located in southwestern Songjiang District, northwestern Jinshan District and southeastern Qingpu District of Shanghai Municipality.

Molluscicidal effect of immersion with 50% wettable powder of niclosamide ethanolamine salt against Oncomelania hupensis on the soil surface and inside the soil layer in winter

To evaluate the molluscicidal effect of 50% wettable powder of niclosamide ethanolamine salt (WPNES) against Oncomelania hupensis on the soil surface and inside the soil layer by immersion method in winter. O. hupensis snails were placed on the soil surface and 2, 5 cm and 10 cm under the soil layer outdoors in winter, and then immersed in 50% WPNES at concentrations of 1 mg/L and 2 mg/L for 1, 3 d and 7 d, while dechlorinated water served as controls. Snail mortality was observed following immersion with 50% WPNES on the soil surface and inside the soil layer. Following immersion with 50% WPNES at concentrations of 2 mg/L and 1 mg/L outdoors in winter, the 3-day corrected snail mortality rates were 98.0% and 76.0% on the soil surface, and the 7-day corrected snail mortality rate was both 100.0%. Following immersion with 50% WPNES at concentrations of 2 mg/L and 1 mg/L outdoors in winter, the 7-day corrected snail mortality rates were 95.5% and 85.6% 2 cm below the soil layer, 66.0% and 6.4% 5 cm below the soil layer. However, the 7-day snail mortality rate swere comparable between the 50% WPNES treatment group (at 2 mg/L and 1 mg/L) and controls 10 cm below the soil layer (both P > 0.05). Immersion of 50% WPNES at a concentration of 2 mg/L for 7 days presents a high molluscicidal efficacy against O. hupensis on the soil surface and 5 cm within the soil layers in winter.

Establishment of a deep learning-based visual model for intelligent recognition of Oncomelania hupensis

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. 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. 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. 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.

Identification of factors affecting Oncomelania hupensis density in Eastern Dongting Lake regions

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. 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. 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. Permenganate index, total phosphorus and the date of the start of submergence affect the O. hupensis snail density in Eastern Dongting Lake regions.

Molluscicidal activity of the Bacillus velezensisis Y6 strain against Oncomelania hupensis and its preliminary mechanisms of molluscicidal actions

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. 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. 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). 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.

Construction of a forecast system for prediction of schistosomiasis risk in China based on the flood information

To create a model based on meteorological data to predict the regions at risk of schistosomiasis during the flood season, so as to provide insights into the surveillance and forecast of schistosomiasis. An interactive schistosomiasis forecast system was created using the open-access R software. The schistosomiasis risk index was used as a basic parameter, and the species distribution model of Oncomelania hupensis snails was generated according to the cumulative rainfall and temperature to predict the probability of O. hupensis snail distribution, so as to identify the regions at risk of schistosomiasis transmission during the flood season. The framework of the web page was built using the Shiny package in the R program, and an interactive and visualization system was successfully created to predict the distribution of O. hupensis snails, containing O. hupensis snail surveillance site database, meteorological and environmental data. In this system, the snail distribution area may be displayed and the regions at risk of schistosomiasis transmission may be predicted using the species distribution model. This predictive system may rapidly generate the schistosomiasis transmission risk map, which is simple and easy to perform. In addition, the regions at risk of schistosomiasis transmission were predicted to be concentrated in the middle and lower reaches of the Yangtze River during the flood period. A schistosomiasis forecast system is successfully created, which is accurate and rapid to utilize meteorological data to predict the regions at risk of schistosomiasis transmission during the flood period.

Intensified surveillance promotes the process towards elimination of schistosomiasis in China

Surveillance is an important part of the national schistosomiasis control program of China, which play a critical role in facilitating the progress towards elimination of schistosomiasis in China. The coverage of schistosomiasis surveillance has shifted from the high-risk regions at the initial stage of the national schistosomiasis control program of China to the current all endemic counties (cities, districts), and the surveillance contents have extended from single surveillance of endemic status to comprehensive surveillance of endemic status, epidemic factors and transmission risks. With the continuous progress towards schistosomiasis elimination, the national schistosomiasis control program has shifted from "extensive control" to surveillance and early warning-based "precision control" in China, which proposes much higher requirements for schistosomiasis surveillance. Currently, the surveillance of schistosomiasis has been covered in all schistosomiasis-endemic counties (cities, districts) of China, and the development of rapid and early identification of Schistosoma japonicum cercariae and S. japonicum-infected Oncomelania hupensis snails will greatly improve the sensitivity of and the duration of responses to schistosomiasis surveillance, which will provide powerful tools for elimination of schistosomiasis in China.

Evaluation of the effect of the water-saving irrigation project on Oncomelania hupensis control in hilly regions of Yixing City, Jiangsu Province

To evaluate the effect of the water-saving irrigation project on Oncomelania hupensis snail control in hilly regions of Yixing City, Jiangsu Province. A retrospective survey combined with cross-sectional investigation was employed. The implementation of the water-saving irrigation development project in Yixing City from 2005 to 2007 was retrospectively collected, and the snail status was collected in regions where the water-saving irrigation project was located and the project-affected regions from 2003 to 2018, to examine the effect of the project on snail control. In addition, a cross-sectional survey was performed to investigate the destruction of the water-saving irrigation project in 2018. A total of 22 water-saving irrigation projects were implemented in 5 townships in hilly regions of Yixing City from 2005 to 2007, where snail habitats were treated covering 266.97 hm2. Before the implementation of the project from 2003 to 2006, cumulative 47.87 hm2 snail habitats were detected in regions where the project was located, and no snails were found in regions where the project was located from the implementation of the project in 2006 to 2018. However, a few snails were found in the project-affected regions in 2017 and 2018. In addition, there were problems found in the later-stage maintenance and management of the project. The water-saving irrigation projects shows a high efficiency on snail control in hilly regions of Yixing City. The later-stage maintenance of the project and monitoring of snails remain to be intensified to enhance the snail control efficiency of the water-saving irrigation project.

Performance of a recombinase - aided amplification assay for detection of Schistosoma japonicum infections in Oncomelania hupensis

To evaluate the efficiency of a recombinase-aided amplification (RAA) assay for the detection of Schistosoma japonicum infections in Oncomelania hupensis snails. A group test was employed. Fifty Oncomelania snails were collected as a detection sample. The detection samples without infected snails were designated as negative specimens, while the detection samples that contained different numbers of infected snails were designated as positive specimens. A total of 10 negative specimens, 10 positive specimens containing 1 infected snail, 20 positive specimens containing 2 infected snails and 10 positive specimens containing 3 infected snails were assigned. Following random grouping, 40 specimens were subject to the florescent RAA assay using a blind method. The miradium shedding method served as a gold standard, and the sensitivity, specificity, Youden's index and coincidence rate of the florescent RAA assay were estimated. In addition, 20 samples consisted of 5 negative specimens and 15 positive specimens with 1, 2 and 3 infected snails respectively were grouped randomly. The same specimens were detected using the crushing method and fluorescent RAA assay with the blind method in a paired-design manner. Then, the test results were compared and analyzed. Florescent RAA assay detected 29 positives in the 30 specimens containing different numbers of infected snails, with a sensitivity of 96.67%, and 8 negatives in the 10 detection specimens without infected snails, with a specificity of 80.00%, showing a Youden's index of 0.77. The coincidence rate was 100% among 10 repeated assays for a detection specimen. In addition, there was no significant difference in the detection of infected snails between the florescent RAA assay and the crushing method (χ2 = 0, P > 0.05), and the actual coincidence rates of the florescent RAA assay and crushing method were 95.00% (19/20) and 90.00% (18/20) with the real results, respectively. Fluorescent RAA assay has a favorable efficiency for the detection of S. japonicum infections in Oncomelania snails, which shows a potential in screening of S. japonicum-infected Oncomelania snails.

Potential impact of flooding on schistosomiasis in Poyang Lake regions based on multi-source remote sensing images

BackgroundFlooding is considered to be one of the most important factors contributing to the rebound of Oncomelania hupensis, a small tropical freshwater snail and the only intermediate host of Schistosoma japonicum, in endemic foci. The aim of this study was to assess the risk of intestinal schistosomiasis transmission impacted by flooding in the region around Poyang Lake using multi-source remote sensing images.MethodsNormalized Difference Vegetation Index (NDVI) data collected by the Landsat 8 satellite were used as an ecological and geographical suitability indicator of O. hupensis habitats in the Poyang Lake region. The expansion of the water body due to flooding was estimated using dual-polarized threshold calculations based on dual-polarized synthetic aperture radar (SAR). The image data were captured from the Sentinel-1B satellite in May 2020 before the flood and in July 2020 during the flood. A spatial database of the distribution of snail habitats was created using the 2016 snail survey in Jiangxi Province. The potential spread of O. hupensis snails after the flood was predicted by an overlay analysis of the NDVI maps in the flood-affected areas around Poyang Lake. The risk of schistosomiasis transmission was classified based on O. hupensis snail density data and the related NDVI.ResultsThe surface area of Poyang Lake was approximately 2207 km2 in May 2020 before the flood and 4403 km2 in July 2020 during the period of peak flooding; this was estimated to be a 99.5% expansion of the water body due to flooding. After the flood, potential snail habitats were predicted to be concentrated in areas neighboring existing habitats in the marshlands of Poyang Lake. The areas with high risk of schistosomiasis transmission were predicted to be mainly distributed in Yongxiu, Xinjian, Yugan and Poyang (District) along the shores of Poyang Lake. By comparing the predictive results and actual snail distribution, we estimated the predictive accuracy of the model to be 87%, which meant the 87% of actual snail distribution was correctly identified as snail habitats in the model predictions.ConclusionsData on water body expansion due to flooding and environmental factors pertaining to snail breeding may be rapidly extracted from Landsat 8 and Sentinel-1B remote sensing images. Applying multi-source remote sensing data for the timely and effective assessment of potential schistosomiasis transmission risk caused by snail spread during flooding is feasible and will be of great significance for more precision control of schistosomiasis.Graphical

Afforestation suppresses Oncomelania hupensis snail density through influencing algae in beaches of the Dongting Lake.

BackgroundOncomelania snails serve as the sole intermediate host for Schistosoma japonicum, one of the most important neglected tropical diseases in the world. Afforestation suppression of the Oncomelania hupensis snail has been a long-term effective national strategy to decrease snail density in China. Many previous studies have made clear that vegetation (biotic factors) and soil (abiotic factors) were the basic requirements for snail survival on beaches. Moreover, a lot of research on snail control has been focused on the specific influencing environmental factors for snail survival, such as the vegetation community structure, species composition, diversity index, and the physical and chemical properties of the soil. Most of the existing research has studied the influence of a single factor on snail population density. Conversely, there have been only a few studies focused on the food sources and food composition of the snails. The current research situation on snail control has indicated that the mechanisms underlying ecological snail control have not been systematically characterized. The question of whether biotic or abiotic factors were more important in influencing snail survival remains unclear. Afforestation on beaches has significantly suppressed snail density in China so far. In this study, we proposed that the reduction of snail density was not affected by a single factor but by the interactions of multiple related factors introduced by afforestation. Moreover, different biotic and abiotic factors have significantly different effects on snail control. Therefore the goal of this study was to evaluate the relative importance and interactions of related biotic and abiotic factors on snail density. Methods: Four major vegetation communities: Sedge, Reed, Artificial poplar (3 years of age) and Artificial poplar (5 years of age), on the beaches of the Yangtze River in China were selected for vegetation and snail surveys, as well as for soil sampling. Structural Equation Model (SEM) analysis was used to assess the interactions of biotic and abiotic factors in the context of snail ecology. The soil properties were considered as abiotic factors, while algae of Chlorophyta, Cyanophyta and Bacillariophyta phyla were considered to be biotic factors. In the path analysis, the total effect between the variables was the sum of the direct and indirect effects.ResultsThe snail density had significant correlations with soil properties, such as water content, bulk density, capillary porosity and pH value, as well as with all three types of soil algae, Chlorophyta, Cyanophyta, and Bacillariophyta. Snail density had a direct negative relationship with capillary porosity and soil bulk density, an indirect negative relationship with soil pH value and an indirect positive relationship with soil water content via soil algae. Meanwhile, as an important food source for the snail, the Chlorophyta, Cyanophyta and Bacillariophyta algae had a significant positive correlation with snail density. High soil pH had a negative impact on Chlorophyta, Bacillariophyta, while soil water content had a positive impact on Chlorophyta, and soil bulk density had a negative impact on Cyanophyta. In addition, the soil pH value and soil bulk density both had negative correlations with soil water content.ConclusionAfforestation of the beach environment can significantly reduce the snail population density by altering ecological factors. Soil algae (biological factors) might be the key element that drives ecological snail control. As important habitat determinants, the impact of the properties of the soil (non-biological factors) on the snail population was largely mediated through soil algae.

Spatio-temporal patterns of Oncomelania hupensis snail habitats in Suzhou, Wuxi and Changzhou cities along the Taihu Lake region

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. 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. 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. 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.

Soil bacterial and fungal diversities and its putative association with the distribution of Oncomelania hupensis in the Dongting Lake marshlands, China

Oncomelania hupensis is the intermediate host of Schistosoma japonicum. In a marshland of Dongting Lake, the abundance of the snail plunged in 1999 and disappeared in 2000, for which the reasons remain unclear. Soil samples were collected from three locations: 1) Qianliang Lake where no snail was found, 2) Junshan Park where remained infested with O. hupensis and 3) Jianxin Farm in between. We compared the physicochemical characteristics and microbial compositions of soil samples from the three sites. All tested physicochemical characteristics of soil samples, except for pH, were similar for samples from Qianliang Lake and Junshan Park marshlands. Both bacterial and fungal community structures varied among the samples from three sites. Fungal diversity was significantly negatively correlated with moisture and total phosphorus and was positively correlated with fluoride and chloride. Soil microbial communities were different between sites with and without O. hupensis snails, but whether some identified abundant taxa are a reason for the disappearance of O. hupensis needs to be confirmed.

Combined transcriptomics and proteomics to identify differential proteins involved in the immune response to the parasite schistosoma japonicum in snail hosts pre-infected with exorchis sp

Oncomelania hupensis is the obligate intermediate host of Schistosoma japonicum, and it also serves as the first intermediate host for Exorchis sp., which uses Parasilurus asoyus as its definitive host rather than humans. In previous studies, Tang et al. found that all S. japonicum larvae can be blocked and killed in O. hupensis pre-infected with Exorchis sp. eggs. However, the molecular and cellular mechanisms involved in this process remain unclear. Therefore, in the present study, a combined transcriptomic and proteomic analysis was performed to identify the differential proteins involved in the immune response to the parasite S. japonicum in the O. hupensis snail host pre-infected with Exorchis sp. trematodes. The results showed that a total of 46,162 unigenes were obtained with 23,535 (50.98%) unigenes annotated in relevant databases, and 3811 proteins from O. hupensis were identified. In addition, iTRAQ-based quantitative proteomic analysis demonstrated that among three groups (OhSj-1_vs_OhN-1, OhE-1_vs_OhN-1 and OhES-1_vs_OhN-1), there were 146 common differential proteins including 44 up-regulated proteins and 90 down-regulated proteins, and 195 differential proteins exclusive to only one experimental group, including 91 up-regulated proteins and 104 down-regulated proteins, which were defined as the Common group and the Only group, respectively. KEGG analysis showed that 15 and 11 differential proteins were annotated in “Infectious diseases” in the Common group and the Only group, respectively, indicating that these proteins may be involved in the snail host immune response to parasite infection. These data will be helpful for better understanding the host-parasite interaction, and could pave the way towards exploring the mechanisms involved in the biological control on S. japonicum in O. hupensis. They also provide valuable information about developing new anti-schistosomiasis strategies.

Effects of copper and cadmium ions on protective enzyme activity in Oncomelania hupensis

To evaluate the effects of Cu2+ and Cd2+ at different concentrations on superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity in Oncomelania hupensis. Cu2+- and Cd2+-containing solutions were prepared at 7 concentrations, and O. hupensis snails were exposed to the solutions for 24 h, of 15 snails in each concentration. Then, the snail body was collected following removal of the snail shell and homogenated, and the SOD, CAT and POS activities were detected in the supernatants. With the increase of the Cu2+ concentration, the SOD activity appeared a rise followed by a reduction in O. hupensis snails, and the CTA activity appeared a decline-rise-decline tendency, while the POD activity showed a tendency towards rise followed by decline. With the increase of the Cd2+ concentration, the SOD activity appeared a rise followed by a reduction in O. hupensis snails, and the CTA activity appeared a decline- rise- decline tendency, while the POD activity showed a decline-rise-decline tendency. Exposure to Cu2+ and Cd2+ at high concentrations results in a decline in the activity of SOD, CAT and POD in O. hupensis at the same time.

Impact of water body environments on the microbial community of Oncomelania hupensis snails in marshlands around the eastern Dongting Lake

To evaluate the effects of water body environments on the microbial community of Oncomelania hupensis snails in marshlands of the eastern Dongting Lake where natural extinction of O. hupensis snails are found, so as to explore the correlation between the natural extinction of O. hupensis snails and the microbial community in snails. Snails were caged water bodies in the Qianliang Lake marshland (Qianliang Lake regions) where natural extinction of snails was found and in the Junshan Park marshland (Junshan Park regions) in the eastern Dongting Lake for 30 days, and then all snails were collected and identified for survival or death. DNA sequencing of the fungi and bacteria was performed in snails before and after immersion in waters, and the biodiversity and abundance were analyzed. The survival rates of O. hupensis snails were 28.0% (70/250) and 64.8% (162/250) in Qianliang Lake regions and Junshan Park regions 30 days after immersion in waters, respectively (χ2 = 81.365, P < 0.01). The number of the fungal community and the biodiversity of the bacterial community were both greater in snails caged in Qianliang Lake regions post-immersion than pre-immersion, and there was a significant difference in the structure of the fungal and bacterial communities. The microbial community with a significant difference included Flavobacteriaceae,which was harmful to O. hupensis snails. The water body environment affects the composition of the microbial community in O. hupensis snails in marshlands with natural snail distinction around the eastern Dongting Lake; however, further studies are required to investigate whether the natural distinction of snails is caused by water body environments-induced changes of the microbial spectrum in O. hupensis snails.

Spatio-temporal distribution of Oncomelania hupensis snails along the Danyang section of the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal

To explore the spatio-temporal characteristics of Oncomelania hupensis snails along the Danyang section of the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal, so as to provide scientific evidence for the dynamic assessment of the risk of snail spread in this region. O. hupensis snail status was collected in the plain regions with waterway networks in the study area from 2012 to 2017. The spatio-temporal variations of snail distribution were investigated along the Danyang section of the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal using buffer zone analysis, spatial autocorrelation, hotspot analysis and standard deviational ellipse with the geographical information system (GIS) tools. The number of snail habitats showed a tendency towards a rise in the study area from 2012 to 2017, and snail habitats were predominantly distributed in the 1 000 m long buffer zone of the Danyang-Jintan-Liyang Canal, notably along the Jiuqu River at the junction between the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal. The distribution of snail habitats appeared spatial autocorrelations in 2014, 2016 and 2017, and the hotspot areas were mainly identified at the junction between the Danyang-Jintan-Liyang Canal and the Beijing-Hangzhou Grand Canal. In addition, the overall distribution of snail habitats was located in the northeastern-southwestern part of the study aera, and gradually shifted to the southern and northern parts with the time. The spatial distribution of O. hupensis snails is complex along the Danyang section of the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal, and there is a risk of snail spread from the upper reaches to the lower reaches, where snail control needs to be intensified.

Spatio-temporal analysis of Oncomelania hupensis along Jiangsu section of the Yangtze River from 2015 to 2017

To investigate the spatio-temporal characteristics of Oncomelania hupensis snails along the Jiangsu section of the Yangtze River, so as to provide evidence for eliminating schistosomiasis and formulating precision control measures in Jiangsu Province. A total of 75 marshlands were randomly sampled from Nanjing, Zhenjiang and Yangzhou cities along the Jiangsu section of the Yangtze River basin, and the spatio-temporal distribution and changing patterns of O. hupensis snails were investigated using the spatial autocorrelation analysis, kernel density analysis and hotspot analysis during the period from 2015 through 2017. There was a spatial autocorrelation in the mean snail density along the Jiangsu section of the Yangtze River basin during the period from 2015 through 2017. The number of living snails and the density of living snails showed an overall decline in Yangzhou City; however, both showed a slight increase in 2016. Kernel density analysis and hotspot analysis showed that the hotspots of living snails were located in the regions neighboring the marshlands at the Yangzhou-Zhenjiang boundary areas along the Jiangsu section of the Yangtze River basin. There is a spatial autocorrelation in the snail distribution with hotspots along the Jiangsu section of the Yangtze River basin, and the surveillance of snails should not be neglected in the marshlands in Jiangsu Province.

Endemic situation of schistosomiasis in People's Republic of China from 2010 to 2017

To understand the epidemic trend of schistosomiasis in China from 2010 to 2017 so as to provide the scientific evidence for schistosomiasis elimination. The information of schistosomiasis control nationwide from 2010 to 2017 was collected, including the endemic of population, status of livestock control, and Oncomelania hupensis snail control. Microsoft Excel was applied for datum management and analysis. From 2010 to 2017, the epidemic of schistosomiasis in China dropped significantly. The decreasing amplitude of estimated number of patients nationwide was 88.46%. Seventy-one acute schistosomiasis patients were reported and 12.68% (9/71) of them were imported. The decreasing rate of cultivated cattle was 50.09%, and the accumulative number of schistosome-infected cattle was 17 239, and the average positive rate of stool examinations decreased from 1.04% to 0.000 22%. The area with snails nationwide was 373 596.18 to 363 068.95 hm2, and the new detected area with snails was 46.71 to 1 346.73 hm2. The area with schistosome-infected snails was 171.68 hm2 in 2012 and it was 9.25 hm2 in 2013. In 72 key monitoring points of 7 endemic provinces, there were 17 schistosome positive points of water body in 2010 and 6 points in 2016. There were some high risk-factors related to schistosomiasis transmission including schisto-some-infected cattle, dogs, and field rats, and the field stools, and the pasture in the area with snails in schistosomiasis monitoring points. The endemic status of schistosomiasis in China has dropped significantly, and the transmission level is very low. However, the infectious source and risk factors in the endemic environments have not be eliminated. Therefore, the infectious source control, health education, snail control, and transmission monitoring should be strengthened, so as to promote the progress of schistosomiasis elimination.

Molluscicidal activity and physiological toxicity of quaternary benzo[c]phenanthridine alkaloids (QBAs) from Macleaya cordata fruits on Oncomelania hupensis.

Schistosomiasis is a serious worldwide parasitic disease. One of the best ways to control schistosomiasis is to control the population of Oncomelania hupensis snails. We sought to identify a high-efficiency biogenic molluscicide against Oncomelania with low toxicity, to avoid chemical molluscicide contamination and toxicity in aquatic organisms. We extracted quaternary benzo[c]phenanthridine alkaloids (QBAs) from Macleaya cordata fruits. Molluscicidal activity of the QBAs against Oncomelania was determined using bioassay. Our results showed that the extracted QBAs had a strong molluscicidal effect. In treatment of O. hupensis with QBAs for 48 h and 72 h, the lethal concentration (LC50) was 2.89 mg/L and 1.29 mg/L, respectively. The molluscicidal activity of QBAs was close to that of niclosamide (ethanolamine salt), indicating that QBAs have potential development value as novel biogenic molluscicides. We also analyzed physiological toxicity mechanisms by examining the activity of several important detoxification enzymes. We measured the effect of the extracted QBAs on the activities of glutathione S-transferase (GST), carboxylesterase (CarE), acid phosphatase (ACP), and alkaline phosphatase (AKP) in the liver of O. hupensis. We found that the effects of QBAs on detoxification metabolism in O. hupensis were time and concentration dependent. The activities of GST, CarE, AKP, and ACP in the liver of snails increased significantly in the early stage of treatment (24 h), but decreased sharply in later stages (120 h), compared with these activities in controls. GST, CarE, AKP, and ACP activity in the liver of snails treated with LC50 QBAs for 120 h decreased by 62.3%, 78.1%, 59.2%, and 68.6%, respectively. Our results indicate that these enzymes were seriously inhibited by the extracted QBAs and the detoxification and metabolic functions of the liver gradually weakened, leading to poisoning, which could be the main cause of death in O. hupensis snails.