Spatio-temporal Transmission and Environmental Determinants of Schistosomiasis Japonica in Anhui Province,China

Background

Schistosomiasis japonica still remains of public health and economic significance in China, especially in the lake and marshland areas along the Yangtze River Basin, where the control of transmission has proven difficult. In the study, we investigated spatio-temporal variations of S. japonicum infection risk in Anhui Province and assessed the associations of the disease with key environmental factors with the aim of understanding the mechanism of the disease and seeking clues to effective and sustainable schistosomiasis control.

Methodology/Principal Findings

Infection data of schistosomiasis from annual conventional surveys were obtained at the village level in Anhui Province, China, from 2000 to 2010 and used in combination with environmental data. The spatio-temporal kriging model was used to assess how these environmental factors affected the spatio-temporal pattern of schistosomiasis risk. Our results suggested that seasonal variation of the normalized difference vegetation index (NDVI), seasonal variation of land surface temperature at daytime (LSTD), and distance to the Yangtze River were negatively significantly associated with risk of schistosomiasis. Predictive maps showed that schistosomiasis prevalence remained at a low level and schistosomiasis risk mainly evolved along the Yangtze River. Schistosomiasis risk also followed a focal spatial pattern, fluctuating temporally with a peak (the largest spatial extent) in 2005 and then contracting gradually but with a scattered distribution until 2010.

Conclusion

The fitted spatio-temporal kriging model can capture variations of schistosomiasis risk over space and time. Combined with techniques of geographic information system (GIS) and remote sensing (RS), this approach facilitates and enriches risk modeling of schistosomiasis, which in turn helps to identify prior areas for effective and sustainable control of schistosomiasis in Anhui Province and perhaps elsewhere in China.     

Spatial Analysis of Schistosomiasis in Hubei Province,China: A GIS-Based Analysis of Schistosomiasis from 2009 to 2013

Background

Schistosomiasis remains a major public health problem in China. The major endemic areas are located in the lake and marshland regions of southern China, particularly in areas along the middle and low reach of the Yangtze River. Spatial analytical techniques are often used in epidemiology to identify spatial clusters in disease regions. This study assesses the spatial distribution of schistosomiasis and explores high-risk regions in Hubei Province, China to provide guidance on schistosomiasis control in marshland regions.

Methods

In this study, spatial autocorrelation methodologies, including global Moran’s I and local Getis–Ord statistics, were utilized to describe and map spatial clusters and areas where human Schistosoma japonicum infection is prevalent at the county level in Hubei province. In addition, linear logistic regression model was used to determine the characteristics of spatial autocorrelation with time.

Results

The infection rates of S. japonicum decreased from 2009 to 2013. The global autocorrelation analysis results on the infection rate of S. japonicum for five years showed statistical significance (Moran’s I > 0, P < 0.01), which suggested that spatial clusters were present in the distribution of S. japonicum infection from 2009 to 2013. Local autocorrelation analysis results showed that the number of highly aggregated areas ranged from eight to eleven within the five-year analysis period. The highly aggregated areas were mainly distributed in eight counties.

Conclusions

The spatial distribution of human S. japonicum infections did not exhibit a temporal change at the county level in Hubei Province. The risk factors that influence human S. japonicum transmission may not have changed after achieving the national criterion of infection control. The findings indicated that spatial–temporal surveillance of S. japonicum transmission plays a significant role on schistosomiasis control. Timely and integrated prevention should be continued, especially in the Yangtze River Basin of Jianghan Plain area.     

Establishing and Applying a Schistosomiasis Early Warning Index (SEWI) in the Lower Yangtze River Region of Jiangsu Province,China

Background

China has made remarkable progress in schistosomiasis control over the past decades. Transmission control has replaced morbidity control as the country moves towards the goal of elimination and the current challenge is to find a sensitive measure capable of gauging transmission risk in low-prevalence areas. The study aims to develop a Schistosomiasis Early Warning Index (SEWI) and demonstrate its use in Jiangsu Province along the lower Yangtze River.

Methodology/Principal Findings

The Delphi approach, a structured communication technique, was used to develop the SEWI. Two rounds of interviews with 30 public health experts specialized in schistosomiasis control were conducted using 40 indicators that reflected different aspects of schistosomiasis transmission and control. The necessity, feasibility, and sensitivity of each indicator were assessed and the weight value of each indicator determined based on these experts'' judgment. The system included 3 first-order indicators, 7 second-order indicators, and 30 third-order indicators. The 3 first-order indicators were endemic status, control measures, social and environmental factors, with the weight values 0.366, 0.343 and 0.291, respectively. For the 7 second-order indicators, the highest weight value was for control measures for snails (0.175) and the lowest for transmission route (0.110). We estimated and mapped the SEWI for endemic areas at the county scale in Jiangsu Province finding that the majority of the endemic areas were characterized as medium transmission risk (SEWI risk values between 0.3 and 0.6), while areas where transmission interruption had been officially declared showed SEWI values <0.30. A few isolated areas (e.g. endemic islands in the Yangtze River) produced SEWI values >0.60. These estimates are largely in agreement with the endemicity levels based on recent epidemiological surveys.

Conclusions/Significance

The SEWI should be useful for estimation of schistosomiasis transmission surveillance, particularly with reference to the elimination of the disease in China.     

Dynamics of spatial clustering of schistosomiasis in the Yangtze River Valley at the end of and following the World Bank Loan Project

The 10-year (1992–2001) World Bank Loan Project (WBLP) contributed greatly to schistosomiasis control in China. However, the re-emergence of schistosomiasis in recent years challenged the long-term progress of the WBLP strategy. In order to gain insight in the long-term progress of the WBLP, the spatial pattern of the epidemic was investigated in the Yangtze River Valley between 1999–2001 and 2007–2008. Two spatial cluster methods were jointly used to identify spatial clusters of cases. The magnitude and number of clusters varied during 1999–2001. It was found that prevalence of schistosomiasis had been greatly reduced and maintained at a low level during 2007–2008, with little change. Besides, spatial clusters most frequently occurred within 16 counties in the Dongting Lake region and within 5 counties in the Poyang Lake region. These findings precisely pointed out the prior places for future public health planning and resource allocation of schistosomiasis.     

Evaluation of mammalian and intermediate host surveillance methods for detecting schistosomiasis reemergence in southwest China

Background

Schistosomiasis has reemerged in China, threatening schistosomiasis elimination efforts. Surveillance methods that can identify locations where schistosomiasis has reemerged are needed to prevent the further spread of infections.

Methods and Principal Findings

We tested humans, cows, water buffalo and the intermediate host snail, Oncomelania hupensis, for Schistosoma japonicum infection, assessed snail densities and extracted regional surveillance records in areas where schistosomiasis reemerged in Sichuan province. We then evaluated the ability of surveillance methods to identify villages where human infections were present. Human infections were detected in 35 of the 53 villages surveyed (infection prevalence: 0 to 43%), including 17 of 28 villages with no prior evidence of reemergence. Bovine infections were detected in 23 villages (infection prevalence: 0 to 65%) and snail infections in one village. Two common surveillance methods, acute schistosomiasis case reports and surveys for S. japonicum-infected snails, grossly underestimated the number of villages where human infections were present (sensitivity 1% and 3%, respectively). Screening bovines for S. japonicum and surveys for the presence of O. hupensis had modest sensitivity (59% and 69% respectively) and specificity (67% and 44%, respectively). Older adults and bovine owners were at elevated risk of infection. Testing only these high-risk human populations yielded sensitivities of 77% and 71%, respectively.

Conclusions

Human and bovine schistosomiasis were widespread in regions where schistosomiasis had reemerged but acute schistosomiasis and S. japonicum-infected snails were rare and, therefore, poor surveillance targets. Until more efficient, sensitive surveillance strategies are developed, direct, targeted parasitological testing of high-risk human populations should be considered to monitor for schistosomiasis reemergence.     

长江经济带森林生态安全评价及时空演变研究

由于森林生态系统的安全关系到人类的生存与发展,因此本文以长江经济带1107个区县为研究对象,运用熵权法、ArcGIS和GeoDA软件、重心分析模型、空间相关分析来分析长江经济带森林生态安全指数（ESI）,结论如下：（1）森林状态指数中,权重最高的指标为森林火灾受灾率,其次为森林有害生物成灾率和林地面积比率;在森林压力指数中,权重最高的指标为政府林业投入强度,其次为年度造林比例和自然保护区占比。（2）从全域来看,森林ESI值长江上游 > 中游 > 下游,长江南岸高于北岸。长江经济带森林ESI值总体水平较低,但在2000-2015年间总体呈上升趋势。从各省看,云南省森林ESI值最高,上海市森林ESI值最低。在此15年间,湖南省森林ESI值提高幅度最大（19.77%）,江苏省提高幅度最小（0.76%）。（3）各支流流域森林ESI值排序：赣江 > 沅江 > 金沙江 > 乌江 > 湘江 > 汉江 > 嘉陵江 > 岷江。从2000-2015年,八大流域的森林ESI值总体呈上升趋势,其中湘江流域增长幅度最大（20.87%）,而金沙江流域增长幅度最小（3.6%）。（4）森林ESI值的重心先后经历了在从南往西、从西往东北和从东北往南等过程。（5）长江经济带森林ESI值有较为显著的集聚性,森林ESI值High-High集聚区域主要分布在四川省和云南省,Low-Low集聚区县主要分布在上海、江苏和安徽,其次在湖北江汉平原、四川成都平原较为集中。（6）基于以上分析,本文建议：①应注重森林火灾、病虫害防治、林业投资、植树造林等工作。②从全域看,生态修复的重点应放在长江下游。从支流流域来看,岷江、嘉陵江和汉江流域应重点加强森林修复工作。③应在上海、江苏、安徽等Low-Low集聚区域加强植树造林和退耕还林的力度,而在四川、云南、江西和浙江等High-High集聚区域适当发展木材加工和林下种植等产业。     

Shifts in the Spatiotemporal Dynamics of Schistosomiasis: A Case Study in Anhui Province,China

Background

The Chinese national surveillance system showed that the risk of Schistosoma japonicum infection fluctuated temporally. This dynamical change might indicate periodicity of the disease, and its understanding could significantly improve targeted interventions to reduce the burden of schistosomiasis. The goal of this study was to investigate how the schistosomiasis risk varied temporally and spatially in recent years.

Methodology/Principal Findings

Parasitological data were obtained through repeated cross-sectional surveys that were carried out during 1997-2010 in Anhui Province, East China. A multivariate autoregressive model, combined with principal oscillation pattern (POP) analysis, was used to evaluate the spatio-temporal variation of schistosomiasis risk. Results showed that the temporal changes of schistosomiasis risk in the study area could be decomposed into two sustained damped oscillatory modes with estimated period of approximately 2.5 years. The POPs associated with these oscillatory components showed that the pattern near the Yangtze River varied markedly and that the disease risk appeared to evolve in a Southwest/Northeast orientation. The POP coefficients showed decreasing tendency until 2001, then increasing during 2002-2005 and decaying afterwards.

Conclusion

The POP analysis characterized the variations of schistosomiasis risk over space and time and demonstrated that the disease mainly varied temporally along the Yangtze River. The schistosomiasis risk declined periodically with a temporal fluctuation. Whether it resulted from previous national control strategies on schistosomiasis needs further investigations.     

Spatially Explicit Modeling of Schistosomiasis Risk in Eastern China Based on a Synthesis of Epidemiological,Environmental and Intermediate Host Genetic Data

Schistosomiasis japonica is a major parasitic disease threatening millions of people in China. Though overall prevalence was greatly reduced during the second half of the past century, continued persistence in some areas and cases of re-emergence in others remain major concerns. As many regions in China are approaching disease elimination, obtaining quantitative data on Schistosoma japonicum parasites is increasingly difficult. This study examines the distribution of schistosomiasis in eastern China, taking advantage of the fact that the single intermediate host serves as a major transmission bottleneck. Epidemiological, population-genetic and high-resolution ecological data are combined to construct a predictive model capable of estimating the probability that schistosomiasis occurs in a target area (“spatially explicit schistosomiasis risk”). Results show that intermediate host genetic parameters are correlated with the distribution of endemic disease areas, and that five explanatory variables—altitude, minimum temperature, annual precipitation, genetic distance, and haplotype diversity—discriminate between endemic and non-endemic zones. Model predictions are correlated with human infection rates observed at the county level. Visualization of the model indicates that the highest risks of disease occur in the Dongting and Poyang lake regions, as expected, as well as in some floodplain areas of the Yangtze River. High risk areas are interconnected, suggesting the complex hydrological interplay of Dongting and Poyang lakes with the Yangtze River may be important for maintaining schistosomiasis in eastern China. Results demonstrate the value of genetic parameters for risk modeling, and particularly for reducing model prediction error. The findings have important consequences both for understanding the determinants of the current distribution of S. japonicum infections, and for designing future schistosomiasis surveillance and control strategies. The results also highlight how genetic information on taxa that constitute bottlenecks to disease transmission can be of value for risk modeling.     

Descriptive Epidemiology of Typhoid Fever during an Epidemic in Harare,Zimbabwe, 2012

Background

Typhoid fever remains a significant public health problem in developing countries. In October 2011, a typhoid fever epidemic was declared in Harare, Zimbabwe - the fourth enteric infection epidemic since 2008. To orient control activities, we described the epidemiology and spatiotemporal clustering of the epidemic in Dzivaresekwa and Kuwadzana, the two most affected suburbs of Harare.

Methods

A typhoid fever case-patient register was analysed to describe the epidemic. To explore clustering, we constructed a dataset comprising GPS coordinates of case-patient residences and randomly sampled residential locations (spatial controls). The scale and significance of clustering was explored with Ripley K functions. Cluster locations were determined by a random labelling technique and confirmed using Kulldorff''s spatial scan statistic.

Principal Findings

We analysed data from 2570 confirmed and suspected case-patients, and found significant spatiotemporal clustering of typhoid fever in two non-overlapping areas, which appeared to be linked to environmental sources. Peak relative risk was more than six times greater than in areas lying outside the cluster ranges. Clusters were identified in similar geographical ranges by both random labelling and Kulldorff''s spatial scan statistic. The spatial scale at which typhoid fever clustered was highly localised, with significant clustering at distances up to 4.5 km and peak levels at approximately 3.5 km. The epicentre of infection transmission shifted from one cluster to the other during the course of the epidemic.

Conclusions

This study demonstrated highly localised clustering of typhoid fever during an epidemic in an urban African setting, and highlights the importance of spatiotemporal analysis for making timely decisions about targetting prevention and control activities and reinforcing treatment during epidemics. This approach should be integrated into existing surveillance systems to facilitate early detection of epidemics and identify their spatial range.     

The Dynamics of Growing Islets and Transmission of Schistosomiasis Japonica in the Yangtze River

We formulate and analyze a system of ordinary differential equations for the transmission of schistosomiasis japonica on the islets in the Yangtze River, China. The impact of growing islets on the spread of schistosomiasis is investigated by the bifurcation analysis. Using the projection technique developed by Hassard, Kazarinoff and Wan, the normal form of the cusp bifurcation of codimension 2 is derived to overcome the technical difficulties in studying the existence, stability, and bifurcation of the multiple endemic equilibria in high-dimensional phase space. We show that the model can also undergo transcritical bifurcations, saddle-node bifurcations, a pitchfork bifurcation, and Hopf bifurcations. The bifurcation diagrams and epidemiological interpretations are given. We conclude that when the islet reaches a critical size, the transmission cycle of the schistosomiasis japonica between wild rats Rattus norvegicus and snails Oncomelania hupensis could be established, which serves as a possible source of schistosomiasis transmission along the Yangtze River.     

Analysing spatio-temporal clustering of meningococcal meningitis outbreaks in Niger reveals opportunities for improved disease control

Background

Meningococcal meningitis is a major health problem in the “African Meningitis Belt” where recurrent epidemics occur during the hot, dry season. In Niger, a central country belonging to the Meningitis Belt, reported meningitis cases varied between 1,000 and 13,000 from 2003 to 2009, with a case-fatality rate of 5–15%.

Methodology/Principal Findings

In order to gain insight in the epidemiology of meningococcal meningitis in Niger and to improve control strategies, the emergence of the epidemics and their diffusion patterns at a fine spatial scale have been investigated. A statistical analysis of the spatio-temporal distribution of confirmed meningococcal meningitis cases was performed between 2002 and 2009, based on health centre catchment areas (HCCAs) as spatial units. Anselin''s local Moran''s I test for spatial autocorrelation and Kulldorff''s spatial scan statistic were used to identify spatial and spatio-temporal clusters of cases. Spatial clusters were detected every year and most frequently occurred within nine southern districts. Clusters most often encompassed few HCCAs within a district, without expanding to the entire district. Besides, strong intra-district heterogeneity and inter-annual variability in the spatio-temporal epidemic patterns were observed. To further investigate the benefit of using a finer spatial scale for surveillance and disease control, we compared timeliness of epidemic detection at the HCCA level versus district level and showed that a decision based on threshold estimated at the HCCA level may lead to earlier detection of outbreaks.

Conclusions/Significance

Our findings provide an evidence-based approach to improve control of meningitis in sub-Saharan Africa. First, they can assist public health authorities in Niger to better adjust allocation of resources (antibiotics, rapid diagnostic tests and medical staff). Then, this spatio-temporal analysis showed that surveillance at a finer spatial scale (HCCA) would be more efficient for public health response: outbreaks would be detected earlier and reactive vaccination would be better targeted.     

Epidemiology of Schistosoma japonicum in China: morbidity and strategies for control in the Dongting Lake region

Dongting Lake, covering a very large surface water area of 2691km(2), is located in Hunan Province in the southern part of the People's Republic of China. It is the second-largest freshwater lake in China and plays an important role in regulating the amount of water in the Yangtze River, China's longest river. The annual water level of the lake changes by as much as 15m, rising in summer and falling in winter. Asian schistosomiasis has been endemic in the Dongting Lake region for centuries and it has had a devastating effect on the public health of the local people. After a difficult struggle for more than four decades, a concerted programme, supported by the World Bank Loan and instigated in 1992, has resulted in remarkable progress in the control of the disease in many endemic areas of the region. However, the great challenge remains to consolidate and maintain the achievements made to date. The Schistosoma japonicum intermediate host (Oncomelania hupensis hupensis) snail habitats are huge, estimated at 1768km(2) in 1996; these are increasing at a rate of 34.7km(2) annually due to high silt deposition from the Yangtze River itself and from the connecting rivers in Hunan province, and construction of embankments in the Dongting Lake region. It is anticipated that the construction of the Three Gorges Super Dam, the largest engineering project ever undertaken, will substantially extend the range of the snail habitats and increase the number of new schistosomiasis cases. In many areas, human re-infections with S. japonicum after drug (praziquantel) treatment remain unacceptably high (up to 20% of those treated are re-infected annually) due to occupational (mainly fishing) water contact. This paper reviews the history and the current status of schistosomiasis control in the lake region, it explores the epidemiological factors which influence the prevalence of the infection and the disease it causes, and it provides insight into future approaches to control which might finally eradicate the infection.     

The distribution of <Emphasis Type="Italic">Biomphalaria</Emphasis> (Gastropoda: Planorbidae) in Lake Victoria with ecological and spatial predictions using Bayesian modelling

Intestinal schistosomiasis is a global disease of enormous public health importance. Assessing the local risk of transmission of the parasite causing the disease requires an appraisal of the distribution of its intermediate snail hosts, Biomphalaria spp.. In East Africa, the Lake Victorian Basin is a major freshwater ecosystem and highly endemic for intestinal schistosomiasis, although detailed distribution data for Biomphalaria have not been collected. We used on-the-ground malacological surveys and conjoint measurement of environmental determinants to develop models for analysis of variables associated with distribution and predictive snail mapping into data-deficient areas. Four expeditions were undertaken to collect snails along the Lake Victoria shoreline, visiting 223 sites overall. Environmental measurements were recorded at the time of inspection and water samples taken for quantification of anion and cation concentrations. The spatial distributions of Biomphalaria choanomphala and Biomphalaria sudanica were modelled in two Bayesian multivariate models: one non-spatial and one spatial with random effects. The results showed that chloride, nitrate, sulphate and the number of sympatric snail species were significant predictors of B. choanomphala whereas habitat, water depth, pH and sulphate were significant predictors for B. sudanica. The range of spatial autocorrelation was large (572.9 km for B. choanomphala and 175.3 km for B. sudanica). Interpolating snail abundance data by kriging revealed two ‘hot-spots’ of high abundance of Biomphalaria. These areas should be targeted in future expeditions to ground-truth the model’s predictions. Our study is the first to use Bayesian methods for determination of biomedically important snail distributions and sets crucial limnological baseline data for assessment of future changes in snail biodiversity in the Lake Victoria Basin.     

Achievements of schistosomiasis control in China

The control of schistosomiasis has been spectacularly successful in terms of controlling endemicity and severity of the disease during the last 50 years. It can be categorized into two stages. From 1955 through 1980, the transmission-control strategy had been widely and successfully carried out. By the end of 1980, the epidemic of schistosomiasis was successfully circumscribed in certain core regions including areas at the middle and low reaches of the Yangtze River and some mountainous areas in Sichuan and Yunnan provinces, where control of schistosomiasis had been demonstrated to be very difficult to be sustained. Therefore, since 1980, schistosomiasis control in China has been modified to employ a stepwise strategy, based on which morbidity control has been given priorities and if possible transmission control has been pursued. However, since snail-ridden areas remain unchanged so far, reinfections occur frequently. This necessitates a maintenance phase to consolidate the achievements in the control of schistosomiasis. In the mean time, we are challenged with some environmental, social and economical changes in terms of controlling schistosomiasis. Successfully controlling schistosomiasis in China is still a long-term task but will be achieved without doubt along with the economic development and the promotion of living and cultural standard of people.     

Response of ecosystem services to socioeconomic development in the Yangtze River Basin,China

The provision of ecosystem services from multifunctional landscapes has contributed to human well-being. However, a general tendency exists to consider only marketed ecosystem services and to ignore non-marketed services, which has become more common when evaluating multiple-ecosystem services at the local level. In this study, we present an integrative index of multiple-ecosystem services (IMES) that avoids this tendency. Our main objective is to evaluate how socioeconomic factors interact with the spatial differences between the supply of and demand for multiple-ecosystem services. GlobCover data and a modified ecosystem service “matrix” are used to quantify and map ecosystem service supply and demand at the municipality level in the Yangtze River Basin, China. We used multiple regression analysis to detect relationships between ecosystem services and socioeconomic factors in municipalities to identify the main drivers of change in the supply of and demand for multiple-ecosystem services at the local level, respectively. The results revealed that 111 municipalities in the Yangtze River Basin (84.7% of the area) had an oversupply of multiple-ecosystem services; these municipalities were primarily situated in the western part of the upper reach and the southeast parts of the middle reach. Undersupplied areas were mainly situated in densely populated municipalities in the northern part of the lower reach and in agricultural municipalities in the northeastern part of the middle reach. The driving factors of changes in multiple-ecosystem services are significantly different not only in terms of the supply, demand and balance between the two but also among the three reaches. These differences in the driving factors among the three reaches can produce incorrect conclusions if an entire basin is considered, particularly for large basins. This information may be of interest to policymakers. The first principal component for the supply of and demand for multiple-ecosystem services exhibits a good correlation with the IMES in the Yangtze River Basin. Additionally, the integrative index of multiple-ecosystem services (including IMES_s and IMES_d) in the study area is relatively reliable according to the sensitivity analysis. Therefore, IMES is an effective tool for aggregating the value of multiple-ecosystem services at local scales. This tool can be used to identify the drivers of changes in multiple-ecosystem services based on the relationships between IMES and socioeconomic factors at the municipality scale. IMES should be useful for policymakers and stakeholders because it can provide important information for local decision-making.     

长三角区域经济社会与生态环境协调发展时空特征及相关性

地区间发展不平衡是制约区域协调发展战略落实的重要障碍之一。基于2010—2019年长三角区域41个地级市的面板数据,构建了包含经济发展、科教事业、基础建设、人民生活、资源环境5个子系统的区域协调发展指标体系,借助GeoDa和ArcGIS软件,运用区域协调发展测度模型、探索性空间数据分析等方法,探讨区域协调发展的时空演变特征及各要素内部相关性。结果表明: 从区域发展的角度来看,长三角区域的发展协调性逐年增强。2010—2019年,上海市、苏州市等地区的经济发展、科教事业水平领先于其他城市,皖西北地区、舟山市、黄山市发展协调程度较弱。从空间自相关的角度来看,长三角区域各子系统平均自相关程度依次为人民生活＞经济发展＞资源环境＞科教事业＞基础建设。其中,经济发展与科教事业的全局莫兰指数呈下降趋势,科教事业没有呈现出显著相关性,基础建设的莫兰指数基本处于较低水平,不同年份浮动程度较大,人民生活在空间上具有明显的高-高与低-低集聚特征,资源环境的全局莫兰指数呈现“V”字形分布。经济建设和科教事业是与区域协调发展相关性最强的两种因素。     

Changes and drivers of zooplankton diversity patterns in the middle reach of Yangtze River floodplain lakes,China

Anthropogenic habitat alteration interferes the natural aquatic habitats and the system''s hydrodynamics in the Yangtze River floodplain lakes, resulting in a serious decline in freshwater biodiversity. Zooplankton communities possess major position in freshwater ecosystems, which play essential parts in maintaining biological balance of freshwater habitats. Knowledge of processes and mechanisms for affecting variations in abundance, biomass, and diversity of zooplankton is important for maintaining biological balance of freshwater ecosystems. Here, we analyzed that the temporal and spatial changes in the structure of zooplankton community and their temporal and spatial variations respond to changes in environmental factors in the middle reach of Yangtze River floodplain lakes. The results showed that zooplankton samples were classified into 128 species, and Rotifera was the most common taxa. Significant seasonal differences were found among the abundance and diversity of zooplankton. Similarly, we also found significant seasonal differences among the biomass of zooplankton functional groups. The spatial turnover component was the main contributor to the β diversity pattern, which indicated that study areas should establish habitat restoration areas to restore regional biodiversity. The NMDS plot showed that the structure of zooplankton community exhibited significant seasonal changes, where the community structure was correlated with pH, water temperature, water depth, salinity, total nitrogen, chlorophyll‐a, and total phosphorus based on RDA. This study highlights that it is very important to ensure the floodplain ecosystem''s original state of functionality for maintaining the regional diversity of the ecosystem as a whole.     

Assessment of the national schistosomiasis control program in a typical region along the Yangtze River,China

Schistosomiasis remains a major public health problem in eastern China, particularly along the Yangtze River Basin. The latest national schistosomiasis control program (NSCP) was implemented in 2005 with the main goal of reducing the rate of infection to less than 5% by 2008 and 1% by 2015. To assess the progress, we applied a Bayesian spatio-temporal model to describe dynamics of schistosomiasis in Guichi, Anhui Province, China, using annual parasitological and environmental data collected within 41 sample villages for the period 2005–2011. Predictive maps of schistosomiasis showed that the disease prevalence remains constant and low. Results of uncertainty analysis, in the form of probability contour maps (PCMs), indicated that the first goal of “infection rate less than 5% by 2008” was fully achieved in the study area. More longitudinal data for schistosomiasis are needed for the assessment of the second goal of “infection rate less than 1% by 2015”. Compared with the traditional way of mapping uncertainty (e.g., variance or mean-square error), our PCMs provide more realistic information for schistosomiasis control.     

Diversification of Schistosoma japonicum in Mainland China revealed by mitochondrial DNA

Background

Schistosoma japonicum still causes severe parasitic disease in mainland China, but mainly in areas along the Yangtze River. However, the genetic diversity in populations of S. japonicum has not been well understood across its geographical distribution, and such data may provide insights into the epidemiology and possible control strategies for schistosomiasis.

Methodology/Principal Findings

In this study infected Oncomelania snails were collected from areas in the middle and lower (ML) reaches of the Yangtze River, including Hubei, Hunan, Anhui, Jiangxi and Jiangsu provinces, and in the upper reaches of the river, including Sichuan and Yunnan provinces in southwest (SW) China. The adult parasites obtained from experimentally infected mice using isolated cercariae were sequenced individually for several fragments of mitochondrial regions, including Cytb-ND4L-ND4, 16S-12S and ND1. Populations in the ML reaches exhibited a relatively high level of diversity in nucleotides and haplotypes, whereas a low level was observed for populations in the SW, using either each single fragment or the combined sequence of the three fragments. Pairwise analyses of F-statistics (Fst) revealed a significant genetic difference between populations in the ML reaches and those in the SW, with limited gene flow and no shared haplotypes in between. It is rather obvious that genetic diversity in the populations of S. japonicum was significantly correlated with the geographical distance, and the geographical separation/isolation was considered to be the major factor accounting for the observed difference between populations in the ML reaches and those in the SW in China.

Conclusions

S. japonicum in mainland China exhibits a high degree of genetic diversity, with a similar pattern of genetic diversity as observed in the intermediate host snails in the same region in China.     

Schistosomiasis mekongi: from discovery to control

In the Mekong River basin, the first case of schistosomiasis was reported in 1957. In the 1960s, endemic areas of the infection, of which profiles were similar to those of schistosomiasis japonica, were discovered in Khong Island, Laos, to Kratie province, Cambodia. A new intermediate snail host; Neotricula aperta was identified and the Mekong strain of schistosome was elevated to a new species: Schistosoma mekongi in 1978. Baseline epidemiological surveillance was performed and schistosomiasis mekongi was described as a public health implication in the middle Mekong River basin. Because of political and economical confusion, endemic situation had become worse, and no control program had been implemented until mass treatment program with praziquantel on Khong Island in 1983. Since then, the prevalence of S. mekongi infection has rapidly decreased in each endemic area. Serological diagnosis has been useful to detect new but low endemic foci. Clinical manifestations of S. mekongi infection are similar to those of S. mansoni and S. japonicum infections. As the reduction of prevalence and intensity of S. mekongi infection, morbidity due to the disease has changed, and ultrasonographic examination is now useful to evaluate morbidity due to schistosomiasis mekongi. Transmission of the disease occurs in a couple of months during low water season. Control of N. aperta is difficult and long-lasting effective control measurements have, so far, not been available. In the next step for controling S. mekongi infection, mass treatment should be continued, and it is needed to combine other appropriate control activities.