Effects of AIBL on Oncomelania hupensis,the intermediate snail host of Schistosoma japonicum:An enzyme histochemical study

Objective:To explore the effect of AIBL on Oncomelania hupensis,the intermediate snail host of Schistosoma japonicum.Methods:The enzyme histochemical profiles of cholineslerase, cytochrome oxidase,lactate dehydrogenase,nitric oxide synthase,and succinate dehydrogenase in the soft tissues of Oncomelania hupensis,the intermediate host snail of Schistosoma japonicum, were analyzed before and after treatment with the active ingredient of Buddleia lindleyana(AIBL), a potent and safe plant molluscicide.Results:Treatment with AIBL induced a notable decrease in the activities of the five enzymes(P【0.01).Conclusions:The results indicate that AIBL impairs the activities of the enzymes,thereby influencing the transfer of neurotransmitter and energy supply in Oncomelania hupensis and ultimately harming their various physiological functions, which are considered to cause death of the species.

Reaction of Oncomelania Hupensis to the Allelopathic Triterpene Sapogenin from Nerium Indicum

This paper has analyzed allelopathic effects ofNerium indicum on Oncomelania hupensis through triterpene sapogenins, a potential molluscicide. The snails were treated under six various concentrations （0, 20, 40, 60, 80, 100 mg/L） of triterpene sapogenins and five periods （1, 2, 3, 4, 5 days）. The mortality of snails was positively correlated with the concentration of triterpene sapogenins and exposure time. The results ofprobit analysis showed that the LD50 （Lethal Dose, 50%） oftriterpenoid saponins from N. indicum by immersion for 2, 3, 4, 5 days were 78.31, 30.26, 20.50, 14.19 mg/L, respectively. And the corresponding 95% confidence intervals were 63.60-108.19, 9.49-44.42, 2.86-30.90, 0.23-22.79 mg/L, respectively. The observations of both scanning electron microscope and transmission electron microscope proved that 40 mg/L triterpene sapogenins could cause apparent damage to the structure of soft tissue, liver and intestine of O. hupensis. The esterase （EST） isozyme electrophoresis in liver of O. hupensis treated by 40 mg/L of the concentrations lixivium of the triterpene sapogenins from N. indicum was analyzed for 24, 48, 72, 96, 120 h, respectively. The activity of enzyme was higher than control water group after been treated up to 24-48 h, and then lowered and disappeared after 72 h. It was implicated that the extracted triterpene sapogenin from N. indicum were promising for controlling the snail, which were also providing the foundation for constructing plant community of oleander to control O. hupensis.

Chromosome-level genome assembly of Oncomelania hupensis: the intermediate snail host of Schistosoma japonicum

Background Schistosoma japonicum is a parasitic flatworm that causes human schistosomiasis, which is a significant cause of morbidity in China, the Philippines and Indonesia.Oncomelania hupensis (Gastropoda: Pomatiopsidae) is the unique intermediate host ofS. japonicum. A complete genome sequence ofO. hupensis will enable the fundamental understanding of snail biology as well as its co-evolution with theS. japonicum parasite. Assembling a high-quality reference genome ofO. hupehensis will provide data for further research on the snail biology and controlling the spread ofS. japonicum.Methods The draft genome was de novo assembly using the long-read sequencing technology (PacBio Sequel II) and corrected with Illumina sequencing data. Then, using Hi-C sequencing data, the genome was assembled at the chromosomal level. CAFE was used to do analysis of contraction and expansion of the gene family and CodeML module in PAML was used for positive selection analysis in protein coding sequences.Results A total length of 1.46 Gb high-qualityO. hupensis genome with 17 unique full-length chromosomes (2n = 34) of the individual including a contig N50 of 1.35 Mb and a scaffold N50 of 75.08 Mb. Additionally, 95.03% of these contig sequences were anchored in 17 chromosomes. After scanning the assembled genome, a total of 30,604 protein-coding genes were predicted. Among them, 86.67% were functionally annotated. Further phylogenetic analysis revealed thatO. hupensis was separated from a common ancestor ofPomacea canaliculata andBellamya purificata approximately 170 million years ago. Comparing the genome ofO. hupensis with its most recent common ancestor, it showed 266 significantly expanded and 58 significantly contracted gene families (P < 0.05). Functional enrichment of the expanded gene families indicated that they were mainly involved with intracellular, DNA-mediated transposition, DNA integration and transposase activity.Conclusions Integrated use of multiple sequencing technologies, we have successfully constructed the genome at the chromosomal-level ofO. hupensis. These data will not only provide the compressive genomic information, but also benefit future work on population genetics of this snail as well as evolutional studies betweenS. japonicum and the snail host.

银杏外种皮对钉螺的杀灭机理

To study the toxicity of extracts of Ginkgo biloba sarcotesta to Oncomelania hupensis,snails were exposed to 40% and 80% of 24 h LC 50 of the extract of Ginkgo bilba for 24 h,choline esterase(ChE),alanine aminotransferase(ALT),alkaline phosphatase(ALP),lactate dehydrogenase(LDH),succino dehydrogenase(SDH),malic dehydrogenase(MDH)activities in cephalopodium and liver were determined by enzyme kinetic assay.Arecoline and niclosamide were used as reference molluscicides.The results showed that sarcotesta of Ginkgo biloba could inhibit ChE,ALT,ALP and MDH activities both in cephalopodium and liver;arecoline could inhibit ChE,ALP,SDH and MDH activities in cephalopodium and ChE,ALT,ALP,SDH and MDH activities in liver.Niclosamide had inhibitory effects upon ChE,ALT,ALP,SDH and MDH activities in cephalopodium,and ChE,ALT,ALP and SDH activities in liver.All three molluscicides did not inhibite LDH activity in cephalopodium and liver.These results indicate that lethal effects of extracts of sarcotesta of Ginkgo biloba are mediated via inhibition of MDH activitiy,and interference with the NADH respiratory chains.Inhibition of vital enzymic mechanisms causes snails to death.

长江中下游地区湖北钉螺线粒体COⅠ基因遗传变异研究

从长江中、下游的江苏省丹徒区和邗江区、浙江省平湖市、湖北省武昌区、江西省余干县和彭泽县、安徽省安庆市和贵池区等5个血吸虫病流行省8个点现场采集湖北钉螺样本,提取基因组DNA、PCR特异性扩增线粒体DNA细胞色素C氧化酶亚单位1(COⅠ)基因,用ClustalX 1.81软件进行多序列比对,MEGA 4.0软件中的Kimura双参数法(Kimura 2-parameter)计算遗传距离,邻接法(NJ)和最大简约法(MP)构建系统发生树。8个地理株湖北钉螺(Oncomelania hupensis)共得到701个同源位点,A/T(60.4%)含量高于C/G(39.6%),所有序列间的平均遗传距离为0.025。进化树显示,江苏丹徒、湖北武昌、江西余干及安徽安庆和贵池5个地理株钉螺形成一个分支,而浙江平湖、江苏邗江和江西彭泽3个地理株钉螺形成另一个分支;但两种方法构建的系统发生树存在差异。长江中下游地区湖北钉螺线粒体COⅠ基因遗传变异显著。

日本血吸虫毛蚴对不同密度和距离湖北钉螺易感性的初步实验观察

为探讨日本血吸虫(Schistosoma japonicum)毛蚴对不同密度、不同距离湖北钉螺(Oncomelania hupensis)易感性,在现场环境下,采用20 000条新鲜孵化出的日本血吸虫毛蚴分别感染1、2、3、5 m处的湖北钉螺,每处钉螺分为5、10、50、100只/袋4个密度组,感染4 h后带回实验室饲养,8周后解剖观察钉螺感染情况。结果发现,距离1、2、3、5 m,密度5、10、50、100只/袋4个组钉螺感染率分别为7.06%、4.35%、2.47%和1.23%;4.55%、4.44%、4.11%和2.27%;2.62%、1.58%、1.29%和1.1%;2.36%、4.04%、2.73%和1.5%。研究表明,钉螺感染概率与距毛蚴投放的距离成反比;但是,未得出钉螺感染率与钉螺密度之间的线性关系。

Comparison of Molluscicide Activity of Ethanol Extract of Sapium sebiferum,Pterocarya stenoptera and Cryptomeria fortunei

[Objective] The aim was to compare the molluscicide activity of ethanol extract of Sapium sebiferum,Pterocarya stenoptera and Cryptomeria fortunei.[Method] The molluscicide activity of ethanol extract of S.sebiferum,P.stenoptera and C.fortunei was determined through poison test of Oncomelania hupensis in laboratory.[Result] S.sebiferum,P.stenoptera and C.fortunei had certain molluscicide effect,and S.sebiferum and C.fortunei had better effect with little difference than P.stenoptera;ethanol could extract the effective molluscicide component from plant more completely,and its molluscicide effect was better than that of plant infusion.[Conclusion] Our study could provide theory reference for the plant selection of controlling O.hupensis ecologically.

Impact of micro-environmental factors on survival, reproduction and distribution of Oncomelania hupensis snails

Background:Schistosomiasis japonica is a chronic parasitic disease that seriously harms people's health.Oncomelonia hupensis is the only intermediate host of Schistosoma japonicum.Jhe micro-environmental factors surrounding the snail have a great impact on the survival,growth and reproduction of 0.hupensis,but there are few relevant systematic analyses until the present.This scoping review aims to identify and summarize the micro-environmental factors that greatly affect 0.hupensis,and to find gaps in research thus to provide directions for future in-depth studies.

Projecting the proliferation risk of Oncomelania hupensis in China driven by SSPs:A multi-scenario comparison and integrated modeling study

Climate change has been known to cause variations in the geographically suitable areas for the schistosome-transmitting Oncomelania hupensis(O.hupensis).The spread of snails not only depends on the degree of warming but also on the socioeconomic development of the next few decades.Shared socioeconomic pathways(SSPs)published by CMIP6 consider carbon emission pathways as well as influences of distinct types of social development and land use on the regional climate,providing the possibility to accurately evaluate the impact of socioeconomic development and climate variation on the spread of O.hupensis.This study employed SSP126,SSP245,SSP370,and SSP585 and the correlative approach to explore the impacts of climate change and socioeconomic development on the potential diffusion areas for O.hupensis in China.The results exhibited strong evidence that O.hupensis will spread in the north of the middle and lower reaches of the Yangtze River and disappear from a small part of its current southern habitat,whereas in Sichuan and Yunnan,O.hupensis may spread slightly to the southeast.The projection also demonstrated that fossil fuel-driven development(SSP585)will be more conducive to the spread of O.hupensis breeding sites in the 2030s,whereas the continuous increase in snail breeding habitats under the regional rivalry path(SSP370)may lead to great challenges in snail control in the long term(2020-2080).

Molluscicidal effectiveness of Luo-Wei,a novel plant-derived molluscicide,against Oncomelania hupensis,Biomphalaria alexandrina and Bulinus truncatus

Background:Control of snail intermediate hosts has been proved to be a fast and efficient approach for interrupting the transmission of schistosomiasis.Some plant extracts have shown obvious molluscicidal activity,and a new compound Luo-Wei,also named tea-seed distilled saponin(TDS),was developed based on the saponins extracted from Camellia oleifera seeds.We aimed to test the molluscicidal activity of 4%TDS against the intermediate host snails in China and Egypt,and evaluate its environmental safety to non-target organisms.Methods:In the laboratory,Oncomelania hupensis,Biomphalaria alexandrina and Bulinus truncatus were exposed to 4%TDS,and the median lethal concentration(LC5o)was estimated at 24,48 and 72 h.In the field,snail mortalities were assessed 1,2,3 and 7 d post-immersion with 2.5 g/m34%TDS and 1,3,7 and 15 d post-spraying with 5 g/m24%TDS.in addition,the acute toxicity of 4%TDS to Japanese quail(Coturnixjaponica),zebrafish(Brachydanio rerio)and freshwater shrimp(Macrobrachium nipponense)was assessed by estimations of LC5o or median lethal dose(LD5o).Results:In the laboratory,the LC5o values of 4%TDS for O.hupensis were 0.701,0.371 and 0.33 mg/L at 24,48 and 72 h,respectively,and 4%TDS showed a 0.33 mg/L 24 h LC5o against B.alexandrina,and a 1.396 mg/L 24 h LCs0 against B.truncatus.Across all study regions,the pooled mortalities of O.hupensis were 72,86,94 and 98%at 1,2,3 and 7 d,following field immersion of 4%TDS at a dose of 2.5 g/m3,and were 69,77,85 and 88%at 1,3,7 and 15 d,following field spraying at 5 g/m2,respectively.4%TDS had moderate toxicity to Japanese quail(7 d LD5o>60 mg/kg)and to shrimp(96 h LCs0=6.28 mg/L;95%CI:3.53-11.2 mg/L),whereas its toxicity to zebrafish was high(96 h LCso--0.15 mg/L;95%CI:0.14-0.17 mg/L).Conclusions:4%TDS is active against O.hupensis,B.alexandrina and B.truncatus under laboratory and field conditions,and it may be a candidate molluscicide of plant origin.

Impact of continuous low water stage on the breeding environment of Oncomelania hupensis: a case study of Poyang Lake area in China

Background Oncomelania hupensis is the only intermediate host of Schistosoma japonicum and plays a decisive role in its transmission.The variation of water level greatly affects the reproduction and growth of snails.Therefore,in this paper,we analyze the variations of water level in the Poyang Lake region from 1993 to 2016 combined with satellite imagery to elucidate the evolution of the snail breeding environment.Methods By employing remote sensing data from 1993 to 2016(April–June and September–November),the vegetation area of Poyang Lake and the vegetation area at different elevations were extracted and calculated.Moreover,the average daily water level data from the four hydrological stations(Hukou station,Xingzi station,Tangyin station and Kangshan station)which represent the typical state of Poyang Lake were collected from 1993 to 2016.The variance of the monthly mean water level,inundation time and the average area were analyzed by variance to find a significance level ofα=0.05.Results According to hydrological data before and after 2003,the average water level after 2003 is significantly lower than that before 2003 in Poyang Lake.After 2003,the time of inundateing the snail breeding period was later in April to June than that before 2003,while the time of wate-falling stage in September to November moved forward after 2003 than before 2003.Of them,the lowest water level affecting the breeding and growing period of O.hupensis in the northern part of Poyang Lake decreased from 11 m to 9 m.After 2003,the expansion of meadow area in the north part of Poyang Lake was mainly concentrated in the elevation of 9–11 m,and the newly increased infested-meadow in the lake area was mainly concentrated in the north part of Poyang Lake.Conclusions By comparing the change of water level characteristics in different parts of the Poyang Lake area as well as changes in meadow area before and after 2003,it is found that the water level changes mainly affect the snail breeding area in the northern part of Poyang Lake.The results are helpful for improving scientific measures for snail control in Jiangxi Province.This approach could also be applicible to Dongting Lake area and other lake areas affected by water level changes and can bring significant guidance for snail control in lake areas.

Three Gorges Dam:the changing trend of snail density in the Yangtze River basin between 1990 and 2019

Background The area of Oncomelania hupensis snail remains around 3.6 billion m^(2),with newly emerging and reemergent habitats continuing to appear in recent years.This study aimed to explore the long-term dynamics of snail density before and after the operation of Three Gorges Dam(TGD).Methods Data of snail survey between 1990 and 2019 were collected from electronic databases and national schistosomiasis surveillance.Meta-analysis was conducted to estimate the snail density.Joinpoint model was used to identify the changing trend and inflection point.Inverse distance weighted interpolation(IDW)was used to determine the spatial distribution of recent snail density.Results A total of 3777 snail survey sites with a precise location of village or beach were identified.For the downstream area,snail density peaked in 1998(1.635/0.11 m^(2),95%CI:1.220,2.189)and fluctuated at a relatively high level before 2003,then declined steadily from 2003 to 2012.Snail density maintained lower than 0.150/0.11 m^(2) between 2012 and 2019.Joinpoint model identified the inflection of 2003,and a significant decreasing trend from 2003 to 2012 with an annual percentage change(APC)being−20.56%(95%CI:−24.15,−16.80).For the upstream area,snail density peaked in 2005(0.760/0.11 m^(2),95%CI:0.479,1.207)and was generally greater than 0.300/0.11 m2 before 2005.Snail density was generally lower than 0.150/0.11 m^(2) after 2011.Snail density showed a significant decreasing trend from 1990 to 2019 with an APC being−6.05%(95%CI:−7.97,−7.09),and no inflection was identified.IDW showed the areas with a high snail density existed in Poyang Lake,Dongting Lake,Jianghan Plain,and the Anhui branch of the Yangtze River between 2015 and 2019.Conclusions Snail density exhibited a fluctuating downward trend in the Yangtze River basin.In the downstream area,the operation of TGD accelerated the decline of snail density during the first decade period,then snail density fluctuated at a relatively low level.There still exists local areas with a high snail density.Long-term control and monitoring of snails need to be insisted on and strengthened.

造林模式对抑螺林土壤功能的影响

血吸虫病危害严重,钉螺(Oncomelania hupensis)作为血吸虫唯一中间宿体,钉螺防治是阻断血吸虫病传播的关键。抑螺林营建是当前进行钉螺防治的有效手段,而林分生长与土壤功能密切相关。本试验以5年生不同造林模式林分为研究对象,分析了活螺生长情况与土壤功能的变化。结果表明:造林模式显著影响了钉螺生长情况,在供试的枫香、樟树、木荷纯林及枫香+樟树+木荷混交林(5∶5∶5)4种林分中,以木荷纯林下活螺框出现率及活螺密度最高,而混交林下活螺框出现率和枫香纯林下活螺密度最低。造林模式影响了土壤含水率、密度、孔隙度、pH值及有机质、全氮、硝态氮含量,但对土壤温度及铵态氮、全磷、有效磷、全钾、有效钾含量无显著影响。整体上,以枫香纯林下林地土壤含水率和pH值最低,密度最小,而土壤孔隙度最大,有机质、全氮、硝态氮含量最高。相关性分析表明,活螺生长与土壤含水率、孔隙度及有机质、全磷含量显著相关。研究认为,造林模式不同,土壤功能不同,抑螺效果也不同。相较香樟、木荷,枫香具有优越的抑螺作用。在进行抑螺林营建中,建议选择土壤疏松透气、排水良好的林地,同时在林地施肥中尽量少施磷肥。

Approaches being used in the national schistosomiasis elimination programme in China:a review

Schistosomiasis japonica,caused by the human blood fluke Schistosoma japonicum,remains a major public health problem in China,although great success has been achieved.The control efforts during the past half-decade,notably the wide implementation of the new integrated strategy with emphasis on control of the source of S.japonicum infection across the country since 2004,has greatly reduced S.japonicum in humans,livestock,and intermediate host Oncomelania hupensis snails,and transmission control of schistosomiasis was achieved in China in 2015.A two-stage roadmap was therefore proposed for schistosomiasis elimination in 2015,with aims to achieve transmission interruption by 2020 and achieve disease elimination by 2025 in the country.During the last two decades,a variety of approaches,which target the epidemiological factors of schistosomiasis japonica have been developed,in order to block the transmission cycle of the parasite.These approaches have been employed in the national or local schistosomiasis control activities,and facilitated,at least in part,the progress of the schistosomiasis elimination programs.Here,we present an approach to control the source of S.japonicum infection,three new tools for snail control,three approaches for detecting and monitoring S.japonicum infection,and a novel model for health education.These approaches are considered to play a great role in the stage moving towards transmission interruption and elimination of schistosomiasis in China.

The Three Gorges Dam:Does it accelerate or delay the progress towards eliminating transmission of schistosomiasis in China?

The Three Gorges Dam,located in the largest endemic area of schistosomiasis in China,is one of the world’s largest hydroelectric projects to date.Some large-scale hydro projects have resulted in schistosomiasis emergence or re-emergence.Therefore,the dam’s potential impact on the transmission of Schistosoma japonicum has raised concerns from medical researchers worldwide.A systematic literature review,coupled with an analysis of data on the water level and snail density in the Yangtze River was conducted to assess the impact of the dam on schistosomiasis transmission after more than 10 years of operation.The dam has significantly altered the water levels in the Yangtze River according to different seasons.These changes directly impact the ecology of the schistosome snail host.Due to the dam,there has been a reduction in the density of Oncomelania snails and/or changes in the distribution of snails.The prevalence of infection with S.japonicum has decreased in the downstream areas of the dam,including in the Dongting and Poyang Lakes.The prevalence of infection with S.japonicum in humans has decreased from 6.80%in 2002(before the dam began operating)to 0.50%in 2012,and the number of people infected with S.japonicum have decreased from 94208 in 2002 to 59200 in 2011 in the Poyang Lake region.The presence of the dam does not seem to affect snail breeding or the prevalence of schistosomiasis in the Three Gorges Reservoir.Overall,the Three Gorges Dam has significantly contributed to changes in hydrology after more than 10 years of the dam operating.The changes caused by the dam,together with integrated control of schistosomiasis,might be accelerating the progress towards eliminating the transmission of S.japonicum in the middle and lower reaches of the Yangtze River.Despite the positive effect the dam is having in controlling S.japonicum transmission,continued surveillance is required to monitor the future ecological impacts of the dam over the long term.

An integrated environmental improvement of marshlands:impact on control and elimination of schistosomiasis in marshland regions along the Yangtze River,China

Background:Schistosomiasis is a global snail-transmitted infectious disease of poverty.Transmission control had been achieved in China in 2015 after the control efforts for over 60 years.Currently,the remaining core regions endemic for Schistosoma japonicum are mainly located in the marshland and lake regions along the Yangtze River basin.Methods:During the period from 2001 through 2015,an integrated environmental improvement of the marshlands was carried out through the implementation of industrial,agricultural and resources development projects in Yizheng County along the Yangtze River.S.japonicum infection in humans,livestock and snails was estimated by serology,stool examination,hatching technique and microscopy during the 15-year study period to evaluate the effect of the integrated environmental improvement on control and elimination of schistosomiasis.Results:A 0.05%overall rate of S.japonicum infection was observed in snails during the 15-year study period,and no infected snails were detected since 2012.The overall prevalence of S.japonicum infection was 0.09%in humans during the study period,and no human infection was found since 2012.In addition,only 13 bovines were identified with S.japonicum infection in 2003 during the 15-year study period,and since 2004,no infection was found in livestock.Conclusion:The results of the present study demonstrate that the implementation of industrial,agricultural and water resources development projects,not only alters snail habitats in marshland regions,and promotes local economic development,which appears a win-to-win strategy to block the transmission of S.japonicum and accelerate socio-economic development along the Yangtze River.

Infestation risk of the intermediate snail host of Schistosomajaponicum in the Yangtze River Basin: improved results by spatial reassessment and a random forest approach

Background:Oncomelania hupensis is only intermediate snail host of Schistosomajaponicum,and distribution of 0.hupensis is an important indicator for the surveillance of schistosomiasis.This study explored the feasibility of a random forest algorithm weighted by spatial distance for risk prediction of schistosomiasis distribution in the Yangtze River Basin in China,with the aim to produce an improved precision reference for the national schistosomiasis control programme by reducing the number of snail survey sites without losing predictive accuracy.Methods:The snail presence and absence records were collected from Anhui,Hunan,Hubei,Jiangxi and Jiangsu provinces in 2018.A machine learning of random forest algorithm based on a set of environmental and climatic variables was developed to predict the breeding sites of the 0.hupensis intermediated snail host of S.japonicum.Different spatial sizes of a hexagonal grid system were compared to estimate the need for required snail sampling sites.The predictive accuracy related to geographic distances between snail sampling sites was estimated by calculating Kappa and the area under the curve(AUC).Results:The highest accuracy(AUC=0.889 and Kappa=0.618)was achieved at the 5 km distance weight.The five factors with the strongest correlation to 0.hupensis infestation probability were:(1)distance to lake(48.9%),(2)distance to river(36.6%),(3)isothermality(29.5%),(4)mean daily difference in temperature(28.1%),and(5)altitude(26.0%).The risk map showed that areas characterized by snail infestation were mainly located along the Yangtze River,with the highest probability in the dividing,slow-flowing river arms in the middle and lower reaches of the Yangtze River in Anhui,followed by areas near the shores of China's two main lakes,the Dongting Lake in Hunan and Hubei and the Poyang Lake in Jiangxi.Conelusions:Applying the machine learning of random forest algorithm made it feasible to precisely predict snail infestation probability,an approach that could improve the sensitivity of the Chinese schistosome surveillance.system.Redesign of the snail surveillance system by spatial bias correction of 0.hupensis infestation in the Yangtze River Basin to reduce the number of sites required to investigate from 2369 to 1747.

Change patterns of oncomelanid snail burden in areas within the Yangtze River drainage after the three gorges dam operated

Background:An"integrated control"strategy has been implemented within seven provinces at highest risk for schistosomiasis along Yangtze River in Peoples'Republic of China(P.R.China)since 2004.Since O ncom elania hupensis is the only intermediate host of the blood fluke(Schistosom a japonicum),controlling the distribution of snails is considered an essential and effeaive way to reduce the risk of schistosomiasis infection.The study aimed to determine the snail area burden and annual trend among provinces with potential risk for schistosomiasis along the Yangtze River,above and below the Three Gorges Dam(TGD).Methods:This retrospective study utilized data previously collected from the National Parasitic Diseases Control Information Management System(NPDCIMS)on annual snail surveys from 2009 to 2017.Descriptive statistics were performed for analyzing the snail burden by provinces,counties,type of environmental location and year,and mapping was conducted to present the snails distribution.Results:From 2009 to 2017,the total snail infested area decreased by 4.22%,from 372253 hm^2 to 356553 hm^2 within the seven high risk provinces.The majority of snails were found in the marshland and lake regions,outside of control embankments.The total snail burden trend remained relatively stable in upstream regions above the TGD from 2010 to 2015,while the trend decreased within downstream regions during this period.In 2016 and 2017,the total snail burden trend increased in both upstream and downstream provinces,however,upstream saw a larger increase.From 2009 to 2017,there were a total of 5990 hm^2 of newly developed snail areas in the seven study provinces and the majority were concentrated in regions below the TGD,accounting for 5610 hm^2(93.70%).Conclusions:There has been a decline in total snail counts from 2009 to 2017.Meanwhile,new snail breeding areas were formed mainly within provinces downstream the TGD due to spread of snails,indicated that the oncomelanid snail would be difficult to completely eliminate.We suggest that the national schistosomiasis integrated control strategy,including mollusciding and environmental modification,will need to be enhanced significantly going forward to achieve a greater reduaion in snail burden and ultimately to achieve elimination.

Apropos:critical analysis of molluscicide application in schistosomiasis control programs in Brazil

Schistosomiasis is a snail-transmitted infectious disease affecting over 200 million people worldwide.Snail control has been recognized as an effective approach to interrupt the transmission of schistosomiasis,since the geographic distribution of this neglected tropical disease is determined by the presence of the intermediate host snails.In a recent Scoping Review published in Infectious Diseases of Poverty,Coelho and Caldeira performed a critical review of using molluscicides in the national schistosomiasis control programs in Brazil.They also described some chemical and plant-derived molluscicides used in China.In addition to the molluscicides described by Coelho and Caldeira,a large number of chemicals,plant extracts and microorganisms have been screened and tested for molluscicidal actions against Oncomelania hupensis,the intermediate host of Schistosoma japonicum in China.Here,we presented the currently commercial molluscicides available in China,including 26%suspension concentrate of metaldehyde and niclosamide(MNSC),25%suspension concentrate of niclosamide ethanolamine salt(SCNE),50%niclosamide ethanolamine salt wettable powder(WPN),4%niclosamide ethanolamine salt dustable powder(NESP),5%niclosamide ethanolamine salt granule(NESG)and the plant-derived molluscicide“Luowei”.These molluscicides have been proved to be active against O.hupensis in both laboratory and endemic fields,playing an important role in the national schistosomiasis control program of China.Currently,China is transferring its successful experiences on schistosomiasis control to African countries.The introduction of Chinese commercial molluscicides to Africa,with adaptation to local conditions,may facilitate the progress towards the elimination of schisosomiasis in Africa.

Distribution pattern of the snail intermediate host of schistosomiasis japonica in the Poyang Lake region of China

Background:With the closure of the Three Gorges Dam in 2003 the hydrology of Poyang Lake was altered dramatically leading to significant changes in the environment.In order to assess the impact on schistosomiasis this study assessed the spatial and temporal patterns of the snail intermediate host,Oncomelania hupensis in the Poyang Lake tributaries.The results of the study have important implications for future snail control strategies leading to disease elimination.Methods:The marshland area surrounding Poyang Lake was divided randomly into 200×200 m vector grids using ArcGIS software,and the surveyed grids were randomly selected by the software.The snail survey was conducted in each selected grid using a survey frame of 50×50 m with one sideline of each grid serving as the starting line.No less than ten frames were used in each surveyed grid with Global Positioning System(GPS)recordings for each.All snails in each frame were collected to determine infection status by microscopy.Altitude data for all frames were extracted from a lake bottom topographic map in order to analyze the average altitude.All snail survey data were collected and statistically analyzed with SPSS 20.0 software in order to determine the difference of the percentage of frames with living snails and mean density of living snails in different regions of Poyang Lake.The altitude of the snail-infested marshlands and snail dens were subsequently identified.Results:A total of 1159 potential snail sampling grids were surveyed,of which 15231 frames(0.1 m2/frame)were investigated.1241 frames had live Oncomelania snails corresponding to 8.15%of the total number of frames.The mean density of living snails was 0.463/0.1 m2 with a maximum of 57 snails per frame.The percent of frames with snails in the southern sector(8.13%)of Poyang Lake did not differ statistically from the north(8.21%).However,the mean density of live snails in the northern sector(0.164/0.1 m2)of the lake was statistically higher(F=6.727;P=0.010)than the south(0.141/0.1 m2).In the south of the lake,the elevation of snail-inhabited marshland ranged between 11-16 m,and could be further subdivided into two snail-concentrated belts at 12-13 m of elevation and 15-16 m of elevation respectively.In the north of the lake,the elevation of snail-inhabited marshland ranged between 9-16 m with the elevation of 12-14 m being the snail-concentrated zone.Conclusions:The elevation of snail-infested marshlands in the Poyang Lake region ranged from 9 to 16 m.The snail distribution and habitat has moved north of the lake and to a lower altitude due to changes in the water level post dam closure.Based on the current geological features of the snail habitant focused mollusciciding should occur in snail dense northern regions with frequent bovine and human traffic.Targeting these identified'hotspots'of transmission will assist in elimination efforts.