Ecological model to predict potential habitats of Oncomelania hupensis, the intermediate host of Schistosoma japonicum in the mountainous regions, China

Schistosomiasis japonica is a parasitic disease that remains endemic in seven provinces in the People's Republic of China (P.R. China). One of the most important measures in the process of schistosomiasis elimination in P.R. China is control of Oncomelania hupensis, the unique intermediate host snail of Schistosoma japonicum. Compared with plains/swamp and lake regions, the hilly/mountainous regions of schistosomiasis endemic areas are more complicated, which makes the snail survey difficult to conduct precisely and efficiently. There is a pressing call to identify the snail habitats of mountainous regions in an efficient and cost-effective manner.; Twelve out of 56 administrative villages distributed with O. hupensis in Eryuan, Yunnan Province, were randomly selected to set up the ecological model. Thirty out of the rest of 78 villages (villages selected for building model were excluded from the villages for validation) in Eryuan and 30 out of 89 villages in Midu, Yunnan Province were selected via a chessboard method for model validation, respectively. Nine-year-average Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) as well as Digital Elevation Model (DEM) covering Eryuan and Midu were extracted from MODIS and ASTER satellite images, respectively. Slope, elevation and the distance from every village to its nearest stream were derived from DEM. Suitable survival environment conditions for snails were defined by comparing historical snail presence data and remote sensing derived images. According to the suitable conditions for snails, environment factors, i.e. NDVI, LST, elevation, slope and the distance from every village to its nearest stream, were integrated into an ecological niche model to predict O. hupensis potential habitats in Eryuan and Midu. The evaluation of the model was assessed by comparing the model prediction and field investigation. Then, the consistency rate of model validation was calculated in Eryuan and Midu Counties, respectively. The final ecological niche model for potential O. hupensis habitats prediction comprised the following environmental factors, namely: NDVI (≥ 0.446), LST (≥ 22.70°C), elevation (≤ 2,300 m), slope (≤ 11°) and the distance to nearest stream (≤ 1,000 m). The potential O. hupensis habitats in Eryuan distributed in the Lancang River basin and O. hupensis in Midu shows a trend of clustering in the north and spotty distribution in the south. The consistency rates of the ecological niche model in Eryuan and Midu were 76.67% and 83.33%, respectively.; The ecological niche model integrated with NDVI, LST, elevation, slope and distance from every village to its nearest stream adequately predicted the snail habitats in the mountainous regions

Modelling the geographical distribution of soil-transmitted helminth infections in Bolivia

The prevalence of infection with the three common soil-transmitted helminths (i.e. Ascaris lumbricoides, Trichuris trichiura, and hookworm) in Bolivia is among the highest in Latin America. However, the spatial distribution and burden of soil-transmitted helminthiasis are poorly documented.; We analysed historical survey data using Bayesian geostatistical models to identify determinants of the distribution of soil-transmitted helminth infections, predict the geographical distribution of infection risk, and assess treatment needs and costs in the frame of preventive chemotherapy. Rigorous geostatistical variable selection identified the most important predictors of A. lumbricoides, T. trichiura, and hookworm transmission.; Results show that precipitation during the wettest quarter above 400 mm favours the distribution of A. lumbricoides. Altitude has a negative effect on T. trichiura. Hookworm is sensitive to temperature during the coldest month. We estimate that 38.0%, 19.3%, and 11.4% of the Bolivian population is infected with A. lumbricoides, T. trichiura, and hookworm, respectively. Assuming independence of the three infections, 48.4% of the population is infected with any soil-transmitted helminth. Empirical-based estimates, according to treatment recommendations by the World Health Organization, suggest a total of 2.9 million annualised treatments for the control of soil-transmitted helminthiasis in Bolivia.; We provide estimates of soil-transmitted helminth infections in Bolivia based on high-resolution spatial prediction and an innovative variable selection approach. However, the scarcity of the data suggests that a national survey is required for more accurate mapping that will govern spatial targeting of soil-transmitted helminthiasis control

Spatial epidemiology in zoonotic parasitic diseases: insights gained at the 1st International Symposium on Geospatial Health in Lijiang, China, 2007

The 1st International Symposium on Geospatial Health was convened in Lijiang, Yunnan province, People's Republic of China from 8 to 9 September, 2007. The objective was to review progress made with the application of spatial techniques on zoonotic parasitic diseases, particularly in Southeast Asia. The symposium featured 71 presentations covering soil-transmitted and water-borne helminth infections, as well as arthropod-borne diseases such as leishmaniasis, malaria and lymphatic filariasis. The work made public at this occasion is briefly summarized here to highlight the advances made and to put forth research priorities in this area. Approaches such as geographical information systems (GIS), global positioning systems (GPS) and remote sensing (RS), including spatial statistics, web-based GIS and map visualization of field investigations, figured prominently in the presentation

Potential impact of climate change and water resources development on the epidemiology of schistosomiasis in China

Schistosomiasis japonica, caused by the blood fluke Schistosoma japonicum, has been endemic in China since ancient times. An estimated 11 million people were infected in the mid-1950s. Recognizing the huge public health significance and the economic impact of the disease, the central government of China implemented a large-scale control programme, which has been sustained and constantly adapted over the past half century. Today, the endemic areas are mainly confined to the lake and marshland regions along the Yangtze River in five provinces, namely Jiangsu, Anhui, Jiangxi, Hunan and Hubei. It is estimated that currently about 800,000 people are infected and that 40 million people are at risk of infection. Historically, the northern geographical limit where schistosomiasis transmission occurred was around the 33°15’ N latitude (e.g. in Baoying county, Jiangsu province), governed by low temperature thresholds. Based on various climate models, the Intergovernmental Panel of Climate Change (IPCC) recently concluded that the Earth has warmed by approximately 0.6°C over the past 100 years. This unusual warming has been particularly pronounced during the last three decades. There is growing consensus that the global trend of climate warming will continue in the 21st century. It has been suggested that climate change could impact on the distribution of the intermediate host snail of S. japonicum, i.e. Oncomelania hupensis. The frequency and transmission dynamics of schistosomiasis can also be affected by waterresource development and management. Among others, the South-to-North Water Transfer (SNWT) project” is currently under construction in China, which intends to divert water from South (the snail-infested Yangtze River) to North (Beijing and Tianjing) via the lakes of Gaoyou, Hongze and others. The implementation and operation of this project could further amplify the negative effects of climate change and facilitate the northward spread of O. hupensis. The main objective of this PhD thesis was to explore the potential impact of climate change and the SNWT project on the future distribution of schistosomiasis japonica, particularly in eastern China. The techniques used were geographic information system (GIS) and remote sensing (RS), coupled with Bayesian spatial statistics, which have become key tools for disease mapping and prediction. First, we reviewed the application of GIS/RS techniques for the epidemiology and control of schistosomiasis in China. The applications included mapping prevalence and intensity data of S. japonicum at a large scale, and identifying and predicting suitable habitats for O. hupensis at a small scale. Other prominent applications were the prediction of infection risk due to ecological transformations, particularly those induced by floods and water-resource development projects, and the potential impact of climate change. We discussed the limitations of the previous work, and outlined potential new applications of GIS/RS techniques, namely quantitative GIS, WebGIS and the utilization of emerging satellite-derived data, as they hold promise to further enhance infection risk mapping and disease prediction. We also stressed current research needs to overcome some of the remaining challenges of GIS/RS applications for schistosomiasis, so that further and sustained progress can be made towards the ultimate goal to eliminate the disease from China. Second, recognizing the advantages of combining GIS/RS techniques with advanced spatial statistical approaches, we developed Bayesian spatio-temporal models to analyze the relationship between key climatic factors and the risk of schistosomiasis infection. We used parasitological data collected annually from 1990 to 1998 by means of cross-sectional surveys carried out in 47 counties of Jiangsu province. Climatic factors, namely land surface temperature (LST) and normalized difference vegetation index (NDVI), were obtained from satellite sensors. Our analysis suggested a negative association between NDVI and the risk of S. japonicum infection, whereas an increase in LST contributed to a significant increase in S. japonicum infection prevalence. Third, in order to better understand the changes in the frequency and transmission dynamics of schistosomiasis in a warmer future China, a series of laboratory experiments were conducted to assess the effect of temperature on the parasite-intermediate host snail interaction. We found a positive linear relationship between the development of. S. japonicum larvae harboured in O. hupensis and temperature. In snails kept at 15.3°C, S. japonicum larvae tend to halt their development, while peak development occurs at 30°C. The temperature at which half of the snails were in hibernation is 6.4°C. A statistically significant positive association was observed between temperature and oxygen intake of O. hupensis at temperatures below 13.0°C. We also detected a logistic relationship between snails’ oxygen intake and their hibernation rate. Our results underscored the important role temperature plays both for the activity of O. hupensis and the development of S. japonicum larvae harboured in the intermediate host snail. Fourth, to substantiate the claim that global warming might alter the frequency and transmission dynamics of S. japonicum in China, we conducted a time-series analysis from 1972-2002, using temperature data from 39 counties of Jiangsu province. Using annual growing degree days (AGDDs) with a temperature threshold of 15.3°C, we forecasted changes in S. japonicum transmission. The final model included a temporal and a spatial component. The temporal trend consisted of second order polynomials in time plus a seasonality component, while the spatial trend was formed by second order polynomials of the coordinates plus the thin plate smoothing splines. The AGDDs of S. japonicum in 2003 and 2006 and their difference were calculated. The temperatures at the 39 locations showed an increasing temporal trend and seasonality with periodicities of 12, 6 and 3 months. The predicted AGDDs increased gradually from north to south in both 2003 and 2006. The increase in AGDD was particularly pronounced in the southern part of the study area. Our results suggest that alterations in the transmission intensity of S. japonicum in south Jiangsu will be more pronounced than in the northern part of the province. Fifth, we further assessed the potential impact of climate change on the distribution of O.hupensis via a spatially-explicit analytical approach. We employed two 30-year composite datasets comprising average monthly temperatures collected at 623 meteorological stations throughout China, spanning the periods 1961-1990 and 1971-2000. Temperature changes were assessed spatially between the 1960s and the 1990s for January, as this is the critical month for survival of O. hupensis. Our results show that the mean January temperatures increased at 590 stations (94.7%), and that China’s average January temperature in the 1990s was 0.96°C higher than 30 years earlier. The historical 0-1°C January isotherm, which has been considered the approximate northern limit of S. japonicum transmission, has shifted from 33°15’ N to 33°41’ N, expanding the potential transmission area by 41,335 km2. This translates to an estimated additional 21 million people at risk of schistosomiasis. Two lakes that form part of the SNWT project are located in this new potential transmission area, namely Hongze and Baima. Finally, we applied GIS/RS techniques to predict potentially new snail habitats around the lakes of Hongze and Baima, as well as Gaoyou lake, which is considered as a habitat where O. hupensis could re-emerge. A model based on flooding areas, NDVI and a wetness index extracted from Landsat images was developed to predict the snail habitats at a small scale. A total of 163.6 km2 of potential O. hupensis habitats were predicted around the three study lakes. In conclusion, our work suggests that global warming and a major water-resource development project could impact on the distribution of S. japonicum and its intermediate host snail in China and demonstrates that the combination of GIS, RS and Bayesian spatial statistical methods is a powerful approach in estimating their extent. The predictions can serve as a basis for health policy makers and disease control managers, and can be of use in the establishment and running of schistosomiasis surveillance systems. It is further suggested that an efficient early warning system should be set up in potential new endemic areas to monitor subtle changes in snail habitats due to climate change and major ecological transformations, and to assure the early detection of emerging and re-emerging schistosomiasis

Modelling environmentally-mediated infectious diseases of humans: transmission dynamics of schistosomiasis in China.

Macroparasites of humans are sensitive to a variety of environmental variables, including temperature, rainfall and hydrology, yet current comprehension of these relationships is limited. Given the incomplete mechanistic understanding of environment-disease interactions, mathematical models that describe them have seldom included the effects of time-varying environmental processes on transmission dynamics and where they have been included, simple generic, periodic functions are usually used. Few examples exist where seasonal forcing functions describe the actual processes underlying the environmental drivers of disease dynamics. Transmission of human schistosomes, which involves multiple environmental stages, offers a model for applying our understanding of the environmental determinants of the viability, longevity, infectivity and mobility of these stages to controlling disease in diverse environments. Here, a mathematical model of schistosomiasis transmission is presented which incorporates the effects of environmental variables on transmission. Model dynamics are explored and several key extensions to the model are proposed

Utilizing Landsat TM and OLI in Predicting \u3ci\u3eOncomelania Hupensis\u3c/i\u3e Habitats Around Poyang Lake Before and After Three Gorges Dam Completion

Schistosomiasis is a parasitic disease caused by the Schistomsoma japonicum flatworm that utilizes the Oncomelania hupensis snail as an intermediate agent. In the People’s Republic of China, these amphibious snails contaminate freshwater systems infecting humans, bovines, and other mammals and have caused significant morbidity for over two thousand years (Wertheim, et al. 2012; Zhang, et al. 2012.) The gravity of this disease prompted the national government to initiate sizable public health programs, such as the World Bank Loan Project (WBLP.) In spite of WBLP\u27s achievements, in 2004, after this program ended, a national survey acknowledged a resurgence of schistosomiasis in various regions including the Poyang Lake area in the Jiangxi Province (Zhang, et al. 2012.) Poyang Lake, since the completion of the Three Gorges Dam in 2009, has experienced significant changes in the lake’s depth and water extent exposing increased land surface, which possesses the potential to alter snail habitats (McManus, et al. 2010.) In analyzing these changes, this project sought to apply remote sensing techniques using multispectral imagery from Landsat 7 and 8 in conjunction with spatial analysis tools offered by Geographic Information Systems (GIS.) Because snail habitats rely heavily on ecological factors, including location of water bodies, submersion periods, and vegetation coverage, this analysis observed these attributes using Modified Difference Water Index (MDWI) and Normalized Difference Vegetation Index (NDVI) calculations. These computations derived from images taken during 2000-2001 and 2013-2014 to observe Poyang Lake before and after Three Gorges Dam completion (Hui, et al. 2008.) Though the examination observed a drastic increase in potential O. hupensis habitats, further analysis that incorporates data unavailable during this project would establish a more complete suitability model (Chen & Lin 2004.

Combined Spatial Prediction of Schistosomiasis and Soil-Transmitted Helminthiasis in Sierra Leone: A Tool for Integrated Disease Control

Two forms of schistosomiasis or bilharzia (intestinal and urogenital) exist in Sierra Leone. The main control strategy for this disease currently is through mass drug administration (MDA) according to the World Health Organization recommended anthelminthic chemotherapy guidelines, and others include snail control, behavior change, and safe water, sanitation and hygiene. Survey on distribution and prevalence of the disease is vital to the planning of MDA in each district. The distribution of intestinal schistosomiasis in the country has been reported previously. The current national survey showed that urogenital schistosomiasis has a specific focal distribution particularly in the central and eastern regions of the country, most prevalent in Bo (24.6%), Koinadugu (20.4%) and Kono (25.3%) districts. Using a simple probabilistic model, this map was combined with the previously reported maps on intestinal schistosomiasis and the combined schistosomiasis prevalence was estimated. The combined schistosomiasis map highlights the presence of high-risk communities in an extensive area in the northeastern half of the country, which provides a tool for planning the national MDA activities

Mapping and modelling neglected tropical diseases and poverty in Latin America and the Caribbean

The prospects and opportunities for application of risk mapping and modelling of the neglected tropical diseases (NTDs) in Latin America are examined with the aim to broaden the interest in geospatial research there. Special reference is made to the potential use of geospatial tools in health planning and implementation of national disease control programmes