三峡建坝后血吸虫病传播危险因素研究Ⅲ库区血吸虫病监测方案的研究

目的了解三峡库区血吸虫病传播危险因素,为三峡库区血吸虫病动态监测提供技术方案。方法在三峡库区进行钉螺生存模拟试验,调查库区流动人口、家畜血吸虫病传染源和钉螺输入库区的潜在危险因素,以及建坝后社会经济发展变化对血吸虫病传播的潜在影响因素,找出库区血吸虫病监测的重点。结果钉螺在三峡库区的适宜环境中能够生长繁殖;血吸虫病传染源主要是往返于血吸虫病流行区的流动人口;从血吸虫病疫区引进花草树木和牲畜,存在将钉螺和动物传染源输入库区的可能;库区社会经济发展可使血吸虫病传入的危险增加,三峡库区已成为血吸虫病的潜在流行区。结论三峡库区血吸虫病监测工作重点应是流动人口、引进的牲畜等血吸虫病传染源和钉螺输入因素的监测。     

2007—2009年三峡库区湖北段血吸虫病监测

采用流行病学方法,监测三峡库区血吸虫病传染源及钉螺孳生情况。结果表明,监测点内未发现本地居民感染血吸虫,但有4例输入性慢性血吸虫病人;未发现钉螺孳生及输入。提示应针对可能引起三峡库区血吸虫病传播的危险因素,加强监测并采取相应的干预措施,有效预防和降低血吸虫病在库区流行的风险。     

Time to set the agenda for schistosomiasis elimination

It is time to raise global awareness to the possibility of schistosomiasis elimination and to support endemic countries in their quest to determine the most appropriate approaches to eliminate this persistent and debilitating disease. The main interventions for schistosomiasis control are reviewed, including preventive chemotherapy using praziquantel, snail control, sanitation, safe water supplies, and behaviour change strategies supported by information, education and communication (IEC) materials. Differences in the biology and transmission of the three main Schistosoma species (i.e. Schistosoma haematobium, S. mansoni and S. japonicum), which impact on control interventions, are considered. Sensitive diagnostic procedures to ensure adequate surveillance in areas attaining low endemicity are required. The importance of capacity building is highlighted. To achieve elimination, an intersectoral approach is necessary, with advocacy and action from local communities and the health community to foster cooperative ventures with engineers, the private sector, governments and non-governmental organizations specialized in water supply and sanitation. Examples of successful schistosomiasis control programmes are reviewed to highlight what has been learnt in terms of strategy for control and elimination. These include St. Lucia and other Caribbean islands, Brazil and Venezuela for S. mansoni; Saudi Arabia and Egypt for both S. mansoni and S. haematobium; Morocco, Tunisia, Algeria, Mauritius and the Islamic Republic of Iran for S. haematobium; Japan and the People's Republic of China for S. japonicum. Additional targets for elimination or even eradication could be the two minor human schistosome species S. guineenisis and S. intercalatum, which have a restricted distribution in West and Central Africa. The examples show that elimination of schistosomiasis is an achievable and desirable goal requiring full integration of preventive chemotherapy with the tools of transmission control. An agenda for the elimination of schistosomiasis would aim to identify the gaps in knowledge, and define the tools, strategies and guidelines that will help national control programmes move towards elimination, including an internationally accepted mechanism that allows verification/confirmation of elimination.     

三峡建坝后血吸虫病传播危险因素研究Ⅱ库区社会经济因素变化对血吸虫病传播的影响

目的了解三峡库区社会经济因素变化对血吸虫病传播的影响。方法采用流行病学、免疫学和社会医学相结合的方法，调查三峡库区流动人口、库区移民、家畜血吸虫病传染源和钉螺输入库区的潜在危险因素，以及建坝后社会经济发展变化对血吸虫病传播的潜在影响因素。结果三峡库区存在从血吸虫病疫区引进花草树木和牲畜，存在将钉螺和动物传染源带入库区的可能；流动人口中有31. 43%曾患过血吸虫病，37. 27%曾接触疫水，1.18%查出血吸虫病抗体阳性，流动人口将成为库区血吸虫病的主要传染源；库区的4大经济产业中，畜牧业、水产养殖业和旅游业均有可能造成传染源的输入。结论三峡库区社会经济发展变化将使库区成为血吸虫病的潜在流行区，应加强监测。     

三峡建坝后四川省血吸虫病流行变化及其对三峡库区的影响

目的 目的 分析三峡建坝后库区上游的四川省血吸虫病流行区的疫情变化及其对三峡库区血吸虫病的传播影 响。 方法 方法 收集分析2000-2012年四川省血吸虫病疫情年报、 2001-2012年血吸虫病监测点资料、 2001年四川省血吸虫 病流行病学抽样调查数据及三峡相关课题研究数据等文献资料, 调查人群、 家畜和钉螺的情况。选择距离库区最近的简 阳市五指乡前进村开展钉螺现场调查。结果 结果 2000-2012年四川省血吸虫病流行区疫情呈持续下降态势, 全省于2008 年达到血吸虫病传播控制。截止2012年, 65.07%的流行县已达到传播阻断标准, 当年全省实有钉螺面积为2 415.80 hm2 , 比2000年减少了60.64%, 自2006年起未查见感染性钉螺。在简阳市五指乡前进村查螺246框, 调查面积17.14 hm2 , 未查见钉螺。结论 结论 三峡建坝后, 四川省血吸虫病流行区范围和有螺面积已明显缩小, 上游流行区疫情向库区扩散的可 能性极小。     

三峡建坝后血吸虫病传播危险因素研究Ⅰ库区生态环境变化对钉螺孳生可能性研究

目的探讨三峡建坝后库区生态环境改变对钉螺在库区生长、繁殖的可能性。方法收集并利用三峡库区有关生态环境及血吸虫病相关研究资料,开展实验室和现场模拟环境钉螺生存繁殖实验及库区现场调查。结果实验室结果表明,模拟的库区土壤环境适宜钉螺生存,且有幼螺孵出,但较现场存活率为低。现场模拟试验结果显示,钉螺存活率宜昌比万州和江津的观测点相对较低(P均<0.05)。土壤湿度与钉螺存活率存在相关性(r=0.3712,P=0.002),土壤pH值、有机质等指标都对钉螺孳生有一定影响。结论在库区模拟的灌溉沟渠和淤积洲滩环境条件下,钉螺可以生存繁殖。应加强对库区潜在钉螺孳生环境的监测,以防钉螺向库区扩散。     

Mathematical modelling of schistosomiasis japonica: comparison of control strategies in the People's Republic of China

We present the first mathematical model on the transmission dynamics of Schistosoma japonicum. The work extends Barbour's classic model of schistosome transmission. It allows for the mammalian host heterogeneity characteristic of the S. japonicum life cycle, and solves the problem of under-specification of Barbour's model by the use of Chinese data we are collecting on human-bovine transmission in the Poyang Lake area of Jiangxi Province in China. The model predicts that in the lake/marshland areas of the Yangtze River basin: (1) once-yearly mass chemotherapy of humans is little better than twice-yearly mass chemotherapy in reducing human prevalence. Depending on the heterogeneity of prevalence within the population, targeted treatment of high prevalence groups, with lower overall coverage, can be more effective than mass treatment with higher overall coverage. Treatment confers a short term benefit only, with prevalence rising to endemic levels once chemotherapy programs are stopped; (2) depending on the relative contributions of bovines and humans, bovine treatment can benefit humans almost as much as human treatment. Like human treatment, bovine treatment confers a short-term benefit. A combination of human and bovine treatment will dramatically reduce human prevalence and maintains the reduction for a longer period of time than treatment of a single host, although human prevalence rises once treatment ceases; (3) assuming 75% coverage of bovines, a bovine vaccine which acts on worm fecundity must have about 75% efficacy to reduce the reproduction rate below one and ensure mid-term reduction and long-term elimination of the parasite. Such a vaccination program should be accompanied by an initial period of human treatment to instigate a short-term reduction in prevalence, following which the reduction is enhanced by vaccine effects; (4) if the bovine vaccine is only 45% efficacious (the level of current prototype vaccines) it will lower the endemic prevalence, but will not result in elimination. If it is accompanied by an initial period of human treatment and by a 45% improvement in human sanitation or a 30% reduction in contaminated water contact by humans, elimination is then possible.     

Awareness and knowledge of schistosomiasis infection and prevention in the "Three Gorges Dam" reservoir area: a cross-sectional study on local residents and health personnel

Background

Schistosomiasis is a severe public health problem in China. It has been predicted that the ecological changes caused by the “Three Gorges Dam”, the world's largest hydropower project, could potentially aggravate the spread of schistosomiasis in the area. This study focused on investigating (a) local residents’ knowledge on the potential risks of schistosomiasis and (b) the capability of local health personnel in preventing schistosomiasis.

Materials and methods

A quantitative survey combined with qualitative interviews was conducted in three counties of the reservoir area during November and December 2008. A total of 1386 inhabitants and 180 local health personals participated in questionnaire survey; 18 inhabitants, 21 health professionals, and 8 local government officials were interviewed.

Results

Of the surveyed inhabitants, 66.3% had no access to safe drinking water; 47.9% had water-contact regularly through farming or swimming; 58.7% did not have hygienic toilets; and only 13.7% used methane for energy. Besides, only 3.8% of the inhabitants had knowledge scores higher than 6 points within the range 0–10. Educational level, occupation and income were significant predictors of knowledge score (P < 0.05). Only about 5% of the inhabitants had some knowledge on schistosomiasis. Among health professionals surveyed, 6.7% had college or higher education; 26.7% had prior schistosomiasis control experience; 75.6% did not receive any relevant training in the past year; and only 52.2% had basic knowledge of schistosomiasis. The logistic regression analysis identified occupation and time at work as significant factors to their knowledge level (P < 0.05). Moreover, the surveillance work was often severely hindered by a shortage of funding, and challenged by monitoring of migrant population. There were very limited training opportunities for the health workers, and almost no health education for inhabitants, if any, neither efficient nor effective.

Conclusion

Although there were multiple risks for potential Schistosoma japonicum infections in the study area, the knowledge level on schistosomiasis and surveillance was relatively low both in local residents and health personnel. Thus, more health education and professional training are urgently required to local residents and health personnel, respectively. By considering limited activities in surveillance and health education been implemented, a strategy plan on intervention to ensure a stronger inter-sectoral cooperation is recommended in order to reduce schistosomiasis transmission risks in this area.     

Morbidity control of schistosomiasis in China

After reviewing the schistosomiasis control program in China with focusing on the socio-economic impact on schistosomiasis endemicity, we introduce the promotion process of morbidity control strategy undertaken before and during the World Bank Loan Project (WBLP) on Schistosomiasis Control. We analyzed the data derived from case study of morbidity control for schistosomiasis, and evaluated the efficacy of chemotherapy. It is suggested that appropriate drug treatment declines worm burden and the intensity of infection as well as prevalence, but chemotherapy alone can hardly reduce the transmission because zoonotic Schistosoma japonicum infection has a great impact on the transmission of the disease. Therefore, the strategies in different (high, medium, and low) transmission areas during the maintenance stage were put forward in consideration of challenges in national control program in the future.     

Epidemiology and control of mekongi schistosomiasis

Since the first case of Schistosoma mekongi infection was reported in 1957, control measures have been implemented in Laos and in Cambodia. Operational research provided the necessary information on parasite epidemiology and the associated morbidity in order to develop adequate control measures. S. mekongi transmission occurs in rocky banks of the river according to a seasonal cycle. Common daily activities of villagers living in the endemic areas constitute the risk factors for infection. The potential role of an animal reservoir is not fully understood. Severe disease is associated with advanced infection status. Signs and symptoms of portal hypertension dominate the clinical situation, and death is usually due to bleeding from ruptured esophageal varices. Schistosomiasis control in both Laos and Cambodia was based on universal treatment campaigns and resulted in a dramatic fall in the prevalence of the infection and in morbidity control. However, even if the disease and the infection have been satisfactorily controlled, transmission still occurs, and in very limited areas the prevalence reaches rates of more than 15%. Today, 60000 people are estimated to be still at risk of infection in Laos and about 80,000 in Cambodia. The new challenge in schistosomiasis control in endemic areas along the Mekong river is to consolidate the results, to establish a sensitive and reliable surveillance system, and finally to adapt control strategies to the low endemic situation. The impoverished nature of the region makes the possibility of sanitation unfeasible, and external support is still needed to sustain activities in the near future and to enable the substantial reduction of risk behaviors.     

Freshwater snail diversity in Benin (West Africa) with a focus on human schistosomiasis

The aim of this study was to conduct a large-scale freshwater snail survey in Benin to assess the malacological diversity and the larval trematode infections with a focus on Schistosoma genus. We conducted 82 freshwater snail surveys in 35 sites ranked in 4 types and belonging to 9 out of 12 departments. Among 19,200 collected snails, 11 species of freshwater snails were identified. Four species of human schistosome transmitting snails, Bulinus forskalii, B. globosus, B. truncatus and Biomphalaria pfeifferi and seven species of non-human schistosome transmitting snails. Although B. forskalii and B. globosus were the most largely distributed snails, none of the Bulinus snails were found naturally infected by schistosomes. B. pfeifferi was found naturally infected by S. mansoni only in one site with a 0.56% prevalence. The most risky areas were Borgou and the four coastal departments. Preliminary contempory information on human schistosomiasis was provided from three different sites. Schistosoma haematobium was found with 57.1%, 96% and 100% prevalences (two of which were new records for this species in Benin) while S. mansoni was restricted to one site (Toho-Todougba) with 74.3% prevalence. Our data showed that both schistosomiasis haematobium and mansoni prevalences increased during the last nineteen years in Toho-Todougba site.     

三峡水库运行后江滩环境变化对江苏省血吸虫病疫情的影响

目的 目的 探讨三峡水库运行后长江江苏段江滩钉螺孳生环境变化对血吸虫病传播的影响。 方法 方法 收集三峡水库 运行前后长江江苏段水情资料、 江苏省沿江地区江滩滩情资料及血吸虫病病情和螺情资料, 并结合典型滩块现场钉螺调 查进行综合分析。结果 结果 三峡水库蓄水后, 长江江苏段水位呈逐年下降趋势。与建坝前 （2002年） 相比, 三峡水库蓄水 175 m后,1-3月份水位提高0.41 m, 4-12月份水位降低0.32 m。在水库建成逐渐运行期间, 江苏省沿江地区血吸虫病疫情 呈下降趋势, 2012年全省沿江地区感染性钉螺面积降为0, 人群血清学检测阳性率为0.73%, 病原学检测阳性率为 0.004%。结论 结论 三峡水库运行后, 长江下游江苏省沿江地区血吸虫病病情和螺情均呈下降趋势。     

Praziquantel treatment of school children from single and mixed infection foci of intestinal and urogenital schistosomiasis along the Senegal River Basin: monitoring treatment success and re-infection patterns

Following major water development schemes in the 1980s, schistosomiasis has become a serious parasitic disease of children living in the Senegal River Basin. Both urogenital (Schistosoma haematobium) and intestinal (Schistosoma mansoni) schistosomiasis can be highly prevalent in school-aged children, with many individuals infected with both parasites. In order to investigate the transmission and re-infection dynamics of both parasite species, single and mixed infection foci at three villages (Nder and Temeye; S. mansoni and S. haematobium foci and Guia; S. haematobium focus) were studied. In each focus infected children were identified and selected for a 12-month study involving two treatments with praziquantel (40 mg/kg) three weeks apart at the beginning of the study and again 6 months into the study. Urine and stool samples were examined for schistosome eggs before and at 6 weeks and 6 months after chemotherapy. Prevalence and intensity of infection were recorded for each child at each time point. Before treatment, in all three villages, the prevalence and intensity of infection was extremely high for both S. mansoni (79–100%) and S. haematobium (81–97%). With the first round of chemotherapy sufficient cure rates (CRs) of both species were achieved in all villages (38–96%) with high egg reduction rates (ERRs) (97–99%). The data show that high and rapid re-infection rates occur, especially for S. mansoni, within a six-month period following treatment. Re-infection must be highly linked to ecological and seasonal factors. The persistence of S. mansoni in Nder could raise concern as levels of infection intensity remain high (geometric mean intensity at baseline 653 epg changed to 705 epg at 12 months) after four rounds of chemotherapy. This phenomenon could be explained by extremely rapid re-infection dynamics or a sub-optimal efficacy of praziquantel against S. mansoni in this village. High intensities in mixed infections may influence disease epidemiology and control warranting further studies. The disease situation in the SRB must be monitored closely and new treatment regimes should be designed and implemented to control schistosomiasis in the school-age population.     

Recent situation of schistosomiasis in Indonesia

Schistosomiasis in Indonesia is limited to two very isolated areas, the Napu and Lindu valleys, in the province of Central Sulawesi. The disease was initially found in 1937 in the village of Tomado. In 1940, a study on schistosomiasis in the Lake Lindu area was initiated and an infection rate of 56% among the people in the three villages of Anca, Tomado and Langko was found. Before a comprehensive control programme was initiated, the infection rate among the population of approximately 4000 people in the Napu valley was very high, e.g. 72% in the village of Winowanga. In 1982, more coordinated and intensive schistosomiasis control measures in the Napu and Lindu valleys were initiated. The average infection rate after control measures were greatly decreased-in Napu valley it was 1.83%, while in Lindu valley it was 0.46%, in 1999. The control approaches can be described over five phases, from 1982 to 1986, up to 1998 to present. In 1998, an agreement between the Government of Indonesia and the Asian Development Bank was signed to develop the schistosomiasis endemic areas of Central Sulawesi into a better socio-economic condition. The objectives of the project are not only to control schistosomiasis, but mainly to protect the National Park which is located between the Lindu and Napu valleys. It is an integrated project named 'Central Sulawesi Integrated Area Development and Conservation Project' and many relevant sectors have been involved in the implementation of this project for the development of the area, including control of schistosomiasis. The implementation of the integrated project started in 1999.     

Micro-scale investigation of intestinal schistosomiasis transmission on Ngamba and Kimi islands,Lake Victoria,Uganda

A study to investigate the effect of environmental predictors on abundance of Biomphalaria, the intermediate host snails of Schistosoma mansoni, was carried out on two small islands in Lake Victoria, Uganda. Malacological surveys were performed at 40 shoreline sites on Kimi and Ngamba islands documenting occurrence of Biomphalaria; other environmental and limnological conditions were also recorded, including gastropod community diversity. Snails were examined for shedding of schistosomes and emerging cercariae were DNA ‘barcoded’. For population genetics analysis of Biomphalaria, snails from four populations from each island were also sequenced. Aquatic phosphate concentrations were higher on Kimi island, confirming greater anthropogenic influence, although, snail species diversity and community assemblages were not significantly different between islands. Bayesian geostatistical models were fitted to assess the effect of environmental factors on Biomphalaria abundance and snails’ risk of shedding schistosome or non-schistosome cercariae. No factors were found to be significant in the spatial model. The local population genetics of S. mansoni and Biomphalaria on each island followed similar patterns as that seen in previous studies on a lake-wide basis. These findings suggest that smaller scale studies may prove useful as proxies for regional level investigations, with reduced logistical and resource output required. However, further research should also include surveys of terminal host parasite burden, as these will affect even micro-scale dynamics of parasite-intermediate host interactions, as well as be important from a public health perspective in their own right.     

三峡库区云阳县居民血防知识及健康教育需求分析

目的了解三峡库区云阳县居民血吸虫病防治知识、健康教育现状及需求,为制定预防血吸虫病爆发提出指导性建议。方法整群随机抽样。抽取云阳县巴阳镇16个村49个组居民共252人,用统一调查表进行调查。结果 252名调查对象血防知识合格率仅为3.97%,合格率较低的人群为女性、文盲和30~40岁及50~60岁的人群。居民最想通过广播、电视,医生讲座咨询等方式获得关于血吸虫病主要症状及防治方面的知识。结论云阳县居民血防意识淡薄,开展健康教育十分必要。     

Schistosomiasis control in the 21st century. Proceedings of the International Symposium on Schistosomiasis,Shanghai, July 4-6, 2001

A total of 120 papers were presented at the International Symposium on Schistosomiasis which was held in Shanghai, July 4-6, 2001 with the theme of Schistosomiasis Control in the 21st Century. In order to focus more attention on the new challenges in control programmes for schistosomiasis as well as show the priority of research areas in new century, we summarize the advances of control programmes and researches in nine areas, including (1) Status of schistosomiasis control programmes; (2) Progress in applied field research; (3) Biology and control approaches of snail hosts; (4) Novel approaches for schistosomiasis control; (5) Pathogenesis and morbidity of the disease; (6) Immunology and vaccine development; (7) Screening of population for chemotherapy in low transmission areas; (8) Sustainable intervention methods in different endemic settings; (9) Impact of animal schistosomiasis on agricultural development and importance of its control; (10) GIS/RS application and environmental changes.     

A longitudinal study of comparison of the Kato-Katz technique and indirect hemagglutination assay (IHA) for the detection of schistosomiasis japonica in China, 2001-2006

From 2001 to 2006, about one-third of the residents aged 5-65 years were selected as the subjects in a schistosome-endemic village located in Jiangxi Province, China. Every 1 year, all participants were analyzed by the Kato-Katz parasitologic examination and indirect hemagglutination assay (IHA). Statistical analysis of the results showed the k indices ranged from 0.250 to 0.347 between the two methods. Assuming the Kato-Katz results as the gold standard reference, the specificity of the IHA was from 60% to 77%, the positive predictive value of this method was from 19% to 30%, and its sensitivity and negative predictive value were more than 97%. The IHA method is unsuitable for individual screening in endemic community with relatively high prevalence (e.g. with >10% or more prevalence). A search for a better diagnostic test that can be applied in field situations in China is essential and should be given high priority.     

三峡大坝建成前影响疟疾流行的相关因素分析与监测结果

目的为了掌握疟疾疫情和按蚊密度动态以及影响疟疾流行的相关因素,为今后库区疟疾防治提供基础数据和依据。方法收集、整理三峡库区与疟疾流行的相关资料、建国后疟疾流行概况、媒介种群及分布等资料。1999年建立三峡库区疟疾监测点,监测疟疾疫情和按蚊种群、密度变化动态。结果三峡库区历史上曾有间日疟和恶性疟流行,20世纪60年代后无恶性疟发生,建国后发生过4次大流行,20世纪80年代末控制流行。传疟媒介有嗜人按蚊和中华按蚊。监测结果显示,疟疾疫情稳定,年发病控制在1/万以下;发热病人血检和儿童IFAT检测结果均为阴性;传疟媒介只有中华按蚊,5～9月叮人率在1～9.6只/人·夜之间,牛房密度在9～326只/小时人工之间。结论三峡水库蓄水前,传染源存在,媒介广泛分布,水库建成蓄水后,流速减缓、水面增宽、消落带积水均为按蚊孳生提供了有利条件,开展监测是必要的。     

Prevalence of Schistosoma japonicum infection of Oncomelania quadrasi snail colonies in 50 irrigated and rain-fed villages of Samar Province, the Philippines

A cross-sectional survey of Oncomelania quadrasi, the intermediate host for Schistosoma japonicum, was conducted between 2004 and 2005 in 50 villages of the Province of Samar, the Philippines. The villages were classified as rain-fed (25) or with some man-made irrigation system (25). The primary objective was to identify all snail colony sites in the 50 villages and to compare snail population density and S. japonicum infection prevalence between the two types of villages. The presence of snail colonies was surveyed along streams, springs, various canals and swampy areas or grass land. A total of 198 colony sites were identified out of the 845 sites surveyed. Of these, a sufficient number of O. quadrasi snails were identified to measure density and infection in 147 sites. Density of O. quadrasi was remarkably uniform across habitats and there were no significant differences across habitats and between village type. The prevalence of infected snails showed more variability among habitats. Indeed, there was an interaction between the type of habitat and the type of village with irrigated villages being associated with a prevalence proportion ratio of 5.76 (1.31, 25.42) as compared to rain-fed villages among streams and springs. No such association was found among other habitats. The results suggest that once a suitable habitat exists, O. quadrasi populations establish and reach a plateau density. These results are discussed in light of possible ecological measures of control.