The ecology of Australorbis glabratus in Puerto Rico

Variations in the distribution of the water-snail Australorbis glabratus, intermediate host of Schistosoma mansoni, have been studied in Puerto Rico, and an attempt made to correlate the distribution with environmental factors. The main sources of bilharziasis infection are flowing waters, but the evidence indicates that the snail is not found in fast-flowing, high-gradient reaches with falls of more than 20 meters per kilometre. The influence of physiographical features on stream gradient is examined and these findings correlated with the biota, water chemistry and human use of the stream. The alluvial areas of the island have many habitats favourable to A. glabratus and constitute the major foci for the transmission of bilharziasis. In general, artificial reservoirs and puddles do not appear to be suitable habitats for the snail. The numerous sink ponds in the Tertiary limestone area on the north coast contain the snail, yet the area is relatively free from bilharziasis, possibly because the ponds are little used.Although the size of A. glabratus populations is limited by many natural enemies, no organism has been found which could be deemed useful for artificial control. Some migratory birds, insects and amphibians may aid the dispersal of the snail. There are indications that the ionic composition of the water may be an important factor in limiting the distribution of A. glabratus. It is suggested that large amounts of carbonates and bicarbonates relative to the amounts of chlorides and sulfates may account for the absence of the snail from some habitats (e.g., limestone streams) and that copper and zinc may be limiting agents in some waters containing small amounts of dissolved solids. Concentrations of 0.050-0.100 p.p.m. of zinc, copper, cadmium or silver in distilled water produce a distress syndrome in the snails, and concentrations of more than 1.0 p.p.m. are rapidly fatal in most cases.     

Further observations on Bulinus (Bulinus) truncatus rohlfsi (Clessin) in Ghana: Seasonal population fluctuations and biology

Bulinus (B.) truncatus rohlfsi is an important snail host of Schistosoma haematobium in Ghana and probably elsewhere in West Africa. Study of this snail in natural habitats in Northern Ghana has shown that the pronounced population fluctuations can be broadly related to the alternating wet and dry seasons and to any marked changes in the aquatic vegetation. An increase in snail density and reproductive activity begins during the rainy season, reaching a peak in the dry season. The onset of the contraction phase in the snail population is often abrupt, although it may be preceded by intense oviposition; during this phase there are but a few widely scattered snails and little reproductive activity with a low level of survival, particularly of juvenile snails. The factors which favour the survival of young specimens are clearly critical in the evolution of the snail population.     

武汉市2000-2009年钉螺面积现状及分析

目的分析螺情,评价效果。方法资料来源于统计报表,钉螺调查采用机械抽样结合环境抽样的方法进行,灭螺采用工程治理和氯硝柳胺药物喷洒方法进行,数据采用11.0版软件处理。结果垸内钉螺面积、易感地带面积,坑塘类钉螺面积和水田类钉螺面积分别下降了72.75%、52.75%、99.76%和91.94%。结论垸内综合治理钉螺孳生地成效显著,重点打击易感地带成绩突出,水田改种旱作是控制水田类钉螺的重要手段。     

Control of Schistosoma mansoni in the Blue Nile Valley of western Ethiopia by mass chemotherapy and focal snail control: a primary health care experience

A simplified combination of human mass treatment with oxamniquine and focal snail control has been applied in a local Schistosoma mansoni control programme in a primary health care setting in the Dalati and Agallu Metti areas of the Ethiopian Blue Nile Valley. Teams of local health personnel and farmers did the daily work under intermittent supervision. Monthly snail surveys near the major villages disclosed a seasonal pattern with many infected snails during the dry season in upper stagnant sections of tributary rivers (1000-1200 m altitude) with favourable temperatures, and few snails in the rainy season. The highest prevalences and intensities of human infection were found in the 15-19 year age group living in the lower altitudes around 700 m. 5067 individuals (50-80% of the local population) were treated with 20-40 mg oxamniquine per kg body weight during the rainy seasons of 1985 (Dalati) and 1986 (Agallu Metti). In the Dalati area cross sectional surveys in 1985 and 1986, before and after the mass treatment, showed a reduction in prevalence from 42.4% to 11.4%, while in the Agallu Metti area a stratified random sample showed a prevalence reduction from 65.4% in 1986 to 7.8% in 1987 and a reduction in the prevalence of moderate to heavy infection (greater than 100 eggs per gram of stool) from 36.9% to 1.4%. Beginning in 1986 niclosamide was applied focally wherever infected snails were found and the monthly snail surveillance continued until 1989. As a result of this combined approach overall snail infection rates were reduced from 11.2% (Dalati) and 32% (Agallu Metti) to zero and 2% respectively. In 1989 the human prevalence was still only 8.6% in Agallu Metti. This programme has shown that it is feasible to control S. mansoni in these very remote localities through the primary health care system.     

Schistosomiasis in Ethiopia

The literature on schistosomiasis in Ethiopia is reviewed with the objective of bringing together in one paper diverse sources which may not be available to those interested in schistosomiasis. Particular attention is given to the influence of altitude and climate, snail ecology and government economic programs on the distribution of schistosomiasis. Out of 365 communities studied between 1961 and 1986 for Schistosomiasis mansoni, cases were reported from 225 (62%), and in 85 (23%) the prevalence ranged from 10 to 92%. Most transmission sites and S. mansoni infections are in agricultural communities along streams between 1300 and 2000 m altitude infested with Biomphalaria pfeifferi, the major snail intermediate host. S. mansoni transmission above 2200 m and below 800 m is precluded in many parts of Ethiopia by low and high water temperatures, respectively. Schistosomiasis haematobium cases have been reported from 30 of the 54 communities studied, 17 of them with infection rates between 14 and 75%. Endemic S. haematobium appears to be confined in its distribution to lowlands below 800 m altitude. The highly focal distribution of S. haematobium transmission is largely due to the nonsusceptibility of most bulinine snails to the Ethiopian strain of the parasite and low water temperatures in the highlands. Water resources development, resettlement programs, refugee migration and other population movements may result in the spread of endemic S. mansoni. Lack of information on snail host/parasite relationships and the ecology of proven and suspected snail hosts does not permit predictions on the spread of endemic S. haematobium. Past and present schistosomiasis control programs in Ethiopia are reviewed and recommendations made for the national control program.     

应用地理信息系统对江宁县钉螺孳生地环境特征的分析

目的　探讨江宁县钉螺孳生地的环境特征。方法　在 Arc View8.1软件支持下 ,建立江宁县钉螺孳生地分布的地理信息系统 ,并利用其方位分析及图层叠加分析钉螺孳生地的空间方位及土壤类型特征。结果　通过建立 2 0 0 0年江宁县钉螺孳生地分布地理信息系统 ,可见江宁县钉螺分布呈聚集性 ;在此基础上 ,空间方位分析显示江宁县山区钉螺孳生地有 78.95 %分布在朝东及朝南等阳光充足的地区 ;进一步通过空间叠加发现 ,江宁县江滩钉螺孳生地的土壤类型主要为灰潮土及水稻土 ,且螺密度以灰潮土 >水稻土 ;虽然山区钉螺孳生地土壤类型较多 ,但还是以紫色土、水稻土及黄棕壤土为主 ,且螺密度以石灰岩土 >紫色土 >黄棕壤土 >水稻土 ,但差异无显著性 (P >0 .0 5 )。同时进一步分析发现 ,在土质沙粘、微碱性、有机质含量丰富的土壤中钉螺密度较大 ,酸性土壤中的钉螺密度则较小。结论　江宁县钉螺在东向或南向阳光充足、土质较粘、土壤偏碱且有机质含量较高的地区较多     

Miracidial attraction by Biomphalaria tenagophila genetically selected for susceptibility]

The attraction of Schistosoma mansoni miracidea by snails genetically selected for susceptibility to infection is considered. Miracidea were exposed to snails or to snail conditioned water in a specially devised three-chamber glass apparatus. Ten miracidea were used for each test and were deposited in the middle chamber (a passage); after 15 minutes, them in each of the number of the three chambers were recorded. In one of the chambers, chosen randomly at each trial, either snails or SCW were used. The snails and the SCW were chosen from either selected snails (highly susceptible) or unselected. The miracidea were of two groups: they came either from susceptible snails in previous generation or were of unselected traits. The results show that only snail generation has importance for the attraction: selected molluscs of susceptible traits do attract the miracidea more.     

2001—2005年苏州高新区血吸虫病监测结果报告

分析江苏省苏州市高新区2004—2021年血吸虫病疫情监测数据,为完善血吸虫病消除策略提供依据。

根据《苏州市血吸虫病、寄生虫病和地方病防治工作意见》和《苏州市血吸虫病、寄生虫病和地方病预防与控制工作技术方案》对2004—2021年血吸虫病人群病情、螺情等进行监测,用Mann⁃Kendall方法和Joinpoint回归方法分析疫情指标（血清学阳性率、有螺框出现率等）变化趋势,用时间序列分析（指数平滑模型）进行螺情预测。

2004—2021年血吸虫病血清学检查共73 680人次,阳性率为0.084%,各年阳性率差异有统计学意义（χ²=70.73,P<0.05）,但阳性率无变化趋势;粪检3 053人次,未检出阳性。共查出有螺面积70.11 hm²,有螺面积呈下降趋势（Z=-1.97,P<0.05）;共查螺30 093框,有螺框出现率为19.038%,各年有螺框出现率差异有统计学意义（χ²=7 203.09,P<0.05）且呈下降趋势（Z=-2.05,P<0.05）;查获活螺26 296只,活螺密度为0.874只·框^-1,活螺密度呈下降趋势（Z=-2.35,P<0.05）;共解剖钉螺12 391只,未发现阳性钉螺。药物灭螺面积264.60 hm²,无变化趋势;环境改造灭螺面积27.77 hm²,呈下降趋势（Z=-2.44,P<0.05）。据预测,2022—2026年有螺框出现率和活螺密度较平稳,但有螺面积波动较大且有增加趋势。

该地无血吸虫病本地病例,未检出阳性钉螺,血吸虫病防治成果得到有效巩固,但有螺面积波动较大且有增加趋势,应做好当地钉螺长期监测工作。

     

应用遥感技术快速确定鄱阳湖区钉螺孳生地的研究

目的　应用地理信息系统和遥感技术 (GIS ,RS)快速确定鄱阳湖区钉螺孳生地带及血吸虫病高危区域。方法　在鄱阳湖区内选择三个血吸虫病重度流行村周围的洲滩 ,用传统方法进行螺情调查 ,卫星定位仪 (GPS)记录有钉螺点的经纬度。运用ERDASIMAGINE软件对鄱阳湖区枯水期的卫星专题制图仪 (TM)遥感片进行计算机非监督分类 ,校正植被指数 (NDVI)和穗帽湿度变换指数 (TC)模型计算 ,并对有螺点相对应TM数据进行综合分析。结果　鄱阳湖区钉螺分布和孳生与洲滩湖草的生长状况及湿度有密切的关系 ,根据现场调查的钉螺分布图 ,有螺点主要分布在计算机非监督分类的 6、7和 8类中 ,进一步模型分析表明 :有螺点主要分布在NDVI >110和TC在 - 10～ 3之间 ,其准确率达 95 %以上。结论　本项研究提示 :运用计算机非监督分类法可大致确定 6、7和 8类为有螺植被环境 ,然后通过NDVI >110确定植被优质区为钉螺的孳生环境 ,最后通过TC =- 10～ 3可确定钉螺最佳孳生地     

Schistosomiasis: new occurrence of Biomphalaria straminea in Belo Horizonte, Minas Gerais

In Belo Horizonte, Minas Gerais, Brazil, the snail Biomphalaria straminea was found in the Pampulha region. Recently the snail was found in ditches in the old Santa Lúcia Reservoir, a now-extinct focus of schistosomiasis transmission by B. glabrata. The snails were collected and examined to verify whether they were naturally infected with Schistosoma mansoni. Negative specimens were used for breeding or infection with the LE strain of S. mansoni from the laboratory and another strain obtained from eggs found in the feces of a schoolchild (VGS) from Belo Horizonte. Among the 1890 snails collected from 1994 to 1995, none were infected with S. mansoni. Among 87 snails collected and exposed to the LE strain, 9 (10.3%) shed cercariae; among 83 snails from F1, and exposed to LE, 10 (12.0%) shed cercariae. Among 88 snails exposed to VGS, 10 (11.3%) shed cercariae. In Belo Horizonte, schistosomiasis is transmitted by B. glabrata and B. tenagophila. However, currently there exists the risk of appearance of a focus in which B. straminea could be the host if prophylactic measures are not taken by the authorities responsible for the construction of a park and lake at that site.     

河道型钉螺孳生地环境特点及灭螺措施

目的 掌握河道型血吸虫病流行区钉螺孳生地的环境特点,提供最优的灭螺措施.方法 选择湘江河长沙段钉螺孳生地现场,进行钉螺分布、钉螺扩散、水文、泥沙和3种灭螺措施效果的观察.结果 湘江长沙段18块洲滩有钉螺分布,面积839 99 hm2.钉螺逆水向上游扩散,年平均可达17.5 km.洲滩的植被93%以上是莎草.湘江水体含沙量较大,汛期5-10月占全年输沙量的70%,因河道水流不畅,所以每年洲滩都有泥沙淤积,厚度一般为1.0 cm,部分低洼地带或水流缓冲处可达7.0 cm左右.湘江一般4月上旬开始涨水,最高洪水位多见于5-7月,最高洪峰持续时间较短,8月开始退水.3种灭螺措施效果比较,实施土埋和翻耕垦种灭螺措施的6块洲滩,灭螺效果好,其中3块效果考核没有发现钉螺,另3块活螺平均密度均减少了95%以上.每年坚持药物灭螺处理的7块洲滩,灭螺效果差,活螺密度没有变化,其中有3块洲滩发现了感染性钉螺.结论 钉螺向上游扩散同样具有较快的速度;洲滩植被以莎草为主;洲滩泥沙淤积主要是5-10月;湘江涨水和退水时间均较长江早;洲滩环境改造灭螺效果好,药物灭螺效果差.     

Cercarial Dermatitis Transmitted by Exotic Marine Snail

Cercarial dermatitis (swimmer’s itch) is caused by the penetration of human skin by cercariae of schistosome parasites that develop in and are released from snail hosts. Cercarial dermatitis is frequently acquired in freshwater habitats, and less commonly in marine or estuarine waters. To investigate reports of a dermatitis outbreak in San Francisco Bay, California, we surveyed local snails for schistosome infections during 2005–2008. We found schistosomes only in Haminoea japonica, an Asian snail first reported in San Francisco Bay in 1999. Genetic markers place this schistosome within a large clade of avian schistosomes, but do not match any species for which there are genetic data. It is the second known schistosome species to cause dermatitis in western North American coastal waters; these species are transmitted by exotic snails. Introduction of exotic hosts can support unexpected emergence of an unknown parasite with serious medical or veterinary implications.     

Ecological observations on the molluscs of significance in the transmission of bilharziasis in Kenya

Further knowledge of the bionomics of bilharziasis vectors is necessary before more effective measures can be taken to control them. Such knowledge, acquired from long-term observations in a variety of habitats, should help to fill some of the gaps in knowledge of molluscan ecology. The present studies were conducted over a period of three to five years and included observations on the proved and suspected vectors of bilharziasis in Kenya. Records were kept of seasonal and regional distribution of the snails, population dynamics and infection rates. Seasonal distribution normally conformed to a definite pattern but was often so influenced by unseasonable weather and interference by man as to render it unrecognizable. Temperature, water fluctuations, types and amount of vegetation, dissolved oxygen and other physical and chemical characteristics of the water were recorded and an attempt was made to assess the importance of the changes in such environmental factors on the prevalence of the snails studied. No correlation could be found between vegetational changes in the habitat and the number of snails present, but complete coverage of the water surface with horizontal vegetation tended to an absence of snails. Except for torrential floods, water fluctuations seemed to have no effect on snail numbers and the chemical and physical properties of the water of negative habitats appeared to be within the range of tolerance of the species observed.     

2016年湖南省钉螺分布状况调查

目的 进一步了解湖南省境内钉螺分布规律,为省内“精准血防”的开展提供参考。 方法 按照国家卫生计生委关于开展全国钉螺普查的相关要求,以中国疾病预防控制中心寄生虫病预防控制所发布的《全国钉螺调查方案》为实施标准,在2016年春季查螺期间采取系统抽样结合环境抽样的方法,对全省现有钉螺环境、历史有螺环境以及可疑环境进行钉螺分布情况调查。建立各环境标准查螺数据库,统计分析现有钉螺面积、流行区类型、环境类型、植被等分布情况。 结果 2016年全省完成钉螺普查392.07万框,调查面积32.49亿m²,查获活螺31.95万只,活螺密度0.081只/框。共查出钉螺环境1 707处,钉螺面积16.63亿m²,其中垸内钉螺912处,面积1 725.48万m²。全省41个疫区县有31个县发现现有钉螺孳生环境,分布在170个乡镇的743个行政村。全省现存钉螺疫区流行类型以湖沼型为主,占总有螺面积97.5%;环境类型以垸外滩地为主,占54.5%;植被环境以杂草为主,占70.5%。全面完成了湖南省41个疫区县级单位钉螺分布调查、螺情资料汇编、有螺环境地理信息采集和地理信息系统(Google Earth平台)地图绘制。 结论 通过此次钉螺普查,全面掌握湖南省钉螺的分布状况,为全省血吸虫病监测与防治提供依据。     

Effect of habitat fragmentation on the schistosome-transmitting snail Oncomelania hupensis in a mountainous area of China

The effect of habitat fragmentation on schistosome-transmitting snails was assessed in an intervention village and a control village in Sichuan Province, China. Snail habitats were fragmented by environmental management. After 2 years, the proportions of quadrats with snails in the fragmented habitats decreased from 9.35% to 2.41% in one patch (c3) and from 12.20% to 6.57% in another patch (c12), whilst the proportions in habitats without fragmentation did not alter significantly. Mean snail density decreased from 0.246 to 0.063 snails/0.11 m² in patch c3 and from 0.356 to 0.177 snails/0.11 m² in patch c12, whilst the mean snail density of other patches did not alter significantly. Most snails from the same patch and/or its remaining patches after fragmentation clustered together in the phylogenetic tree, except for c1, c3 and its remaining patches (c5, c6 and c11). Snail habitats in the study zone exhibited visible fragmentation. Habitat fragmentation could decrease the snail population size and limit migration and dispersal of snails between patches.     

2008-2011年浙江省省级血吸虫病监测点监测结果分析

目的掌握浙江省省级血吸虫病监测点疫情状况,为制定防治对策提供参考。方法按《浙江省血吸虫病监测点监测方案》要求,在全省9个省级血吸虫病监测点开展螺情、病情及相关因素等调查。结果 2008-2011年监测点螺情监测在6个监测点查出有螺面积54 970m2,2011年有螺面积、有螺框出现率和活螺密度分别较2008年下降了71.81%、80.99%和93.79%,未查到输入性钉螺和感染性钉螺。病情监测未发现本地急性感染病人、新感染病人(畜),尚存4例历史晚期血吸虫病患者,发现14例输入性血吸虫病患者,其中2例为急性血吸虫病患者。结论监测结果基本反映了浙江省达到血吸虫病传播阻断标准后当前的疫情状况和防治现状,残存钉螺和输入性传染源的存在增加了血吸虫病重新流行的危险性,必需加强本地螺情和输入性传染源的监测。     

An outbreak of acute schistosomiasis at Porto de Galinhas beach, Pernambuco, Brazil

We recently confirmed several cases of acute schistosomiasis in Porto de Galinhas beach, Northeast Brazil. A total of 662 patients were diagnosed by parasitological and clinical examinations. The infection likely occurred during the September 7 national holiday, when heavy rainfall flooded the Ipojuca River and people were infected when the water covered their yards. Families were continuously exposed to infection for a period of three weeks until the water had completely dried up. Previous investigation suggests that snail vectors were introduced as a result of landfill in marshy areas. The swamp-flooding of such areas facilitated the emergence of slums surrounded by snail breeding sites. Heavy rainfall caused open-air sewage ditches to overflow, allowing for infection of snails by Schistosoma mansoni. Thus, continuous floods were responsible for the spread of human infection. Clinical and laboratory results identified 62% of acute cases of S. mansoni. Complementary studies are being conducted to define the impact and epidemiological meaning of the acute schistosomiasis outbreak.     

The action of very low concentrations of sodium pentachlorophenate on freshly laid eggs of Australorbis glabratus

This paper describes experiments to test the action of low concentrations of sodium pentachlorophenate against freshly laid eggs of Australorbis glabratus, the principal intermediate host of Schistosoma mansoni in the western hemisphere. Techniques for collecting the eggs without damage and for conducting the tests are described. This compound was found to be 4-10 times more toxic for the eggs than for the adult snails. Strain differences in susceptibility of the eggs were also found. The demonstration of greater susceptibility of the eggs to the compound suggests that snail control might be accomplished more economically in some situations if the chemical were directed primarily against the eggs. The possibility of using eggs instead of adults for screening potential molluscicides is also discussed.     

Chemotherapy-based control of schistosomiasis haematobia. 3. Snail studies monitoring the effect of chemotherapy on transmission in the Msambweni area, Kenya

Regular snail sampling was performed at 40 sites, representing the principal snail habitats, during a 4 year chemotherapy programme targetted at school-children in the Msambweni area of the coastal plain of Kenya. Populations of Bulinus africanus group snails, primarily from pools, showed seasonal variations, dropping when sites dried out and rising when they were refilled by the rains. Transmission, judged by the recovery of snails shedding typical fucocercous cercariae, continued throughout the treatment period at very low levels (less than 1% of the snails collected were infected) with peaks in October/November and in January/February after seasonal rains. Spatially, most infected snails were recovered from 2 large pools near the sea, close to the school that responded least well to the initial chemotherapy programme. Later, infected snails were found sporadically in inland pools, rice fields and temporary streams near another school where there was evidence of substantial reinfection as the study progressed. The snail findings are consistent with a reduction but not elimination of transmission associated with the chemotherapy programme.     

Seasonal and Geographic Distribution of Cercarial Infection in Lymnaea gedrosiana (Pulmunata: Lymnaeidae) In North West Iran

Background

Trematodes are a diverse group of endoparasites which require molluscan and vertebrate animals as intermediate and definitive hosts in their life cycle. The present study was carried out to determine the diversity and geographic distribution of infection with trematodes''cercariae in the snail Lymnaea gedrosiana from north-west Iran.

Methods

A total number of 6759 Lymnaeidae snails were collected from 28 snail habitats; of these L. gedrosiana was the prevalent snail (74.37%) which examined for cercarial infection by shedding method.

Results

The overall infection rate was 8.03%. The most frequent trematodes cercariae in the snail were xiphidiocercariae (81.98%), furcocercariae (32.26%), echinostome cercariae (5.19%), and monostome cercariae (1.24%). The highest infection rate in L. gedrosiana (100%) was with echinostome cercariae from Golestaneh in autumn.

Conclusion

Due to the important role of pond snails in transmission of cercariae to fish as a source of zoonotic diseases, it is essential to estimate the distribution and abundance of the snails and the rate of their infection with different trematodes’ cercariae, and establish control programs in each region.