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Huang Q, Gurarie D, Ndeffo-Mbah M, Li E, King CH. Schistosoma transmission in a dynamic seasonal environment and its impact on the effectiveness of disease control. J Infect Dis 2020; 225:1050-1061. [PMID: 33263735 PMCID: PMC8921996 DOI: 10.1093/infdis/jiaa746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Accepted: 11/30/2020] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND A seasonal transmission environment including seasonal variation of snail population density and human-snail contact patterns can affect the dynamics of Schistosoma infection and the success of control interventions. In projecting control outcomes, conventional modeling approaches have often ignored seasonality by using simplified intermediate-host modeling, or by restricting seasonal effects through use of yearly averaging. METHODS We used mathematical analysis and numerical simulation to estimate the impact of seasonality on disease dynamics and control outcomes, and to evaluate whether seasonal averaging or intermediate-host reduction can provide reliable predictions of control outcomes. We also examined whether seasonality could be used as leverage in creation of effective control strategies. RESULTS We found models that used seasonal averaging could grossly overestimate infection burden and underestimate control outcomes in highly seasonal environments. We showed that proper intra-seasonal timing of control measures could make marked improvement on the long-term burden reduction for Schistosoma transmission control, and we identified the optimal timing for each intervention. Seasonal snail control, implemented alone, was less effective than mass drug administration, but could provide additive impact in reaching control and elimination targets. CONCLUSION Seasonal variation makes Schistosoma transmission less sustainable and easier to control than predicted by earlier modeling studies.
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Affiliation(s)
- Qimin Huang
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, Cleveland, USA
| | - David Gurarie
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, Cleveland, USA.,Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, Cleveland, USA
| | - Martial Ndeffo-Mbah
- Department of Veterinary and Integrative Biosciences, College of Veterinary and Biomedical Sciences, Texas A&M University, College Station, USA.,School of Public Health, Texas A&M University, College Station, USA
| | - Emily Li
- Ascension St. Vincent Indianapolis, Family Medicine Residency, Indianapolis, USA
| | - Charles H King
- Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, Cleveland, USA.,Schistosomiasis Consortium for Operational Research and Evaluation, University of Georgia, Athens, USA.,WHO Collaborating Centre for Research and Training for Schistosomiasis Elimination, Cleveland, USA
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2
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Dong Y, Du CH, Zhang Y, Wang LF, Song J, Wu MS, Yang WC, Lv S, Zhou XN. Role of ecological approaches to eliminating schistosomiasis in Eryuan County evaluated by system modelling. Infect Dis Poverty 2018; 7:129. [PMID: 30593286 PMCID: PMC6309097 DOI: 10.1186/s40249-018-0511-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Accepted: 12/06/2018] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND Schistosomiasis was severely prevalent in Yunnan Province, and it is difficult to achieve its elimination by convention approaches due to complexity of the nature. We explored the comprehensive model to eliminate schistosomiasis in Eryuan County, Yunnan Province, the People's Republic of China, through integration with the ecological protection programme in Erhai Lake, in order to promote an efficient elimination strategy. We expected that this model is able to be tailored to other local settings, which help achieve the goal of precisely eliminating the disease in Yunnan Province. METHODS Eryuan County of Yunnan Province was chosen as the study area, where the data on environmental protection activities in Erhai Lake and on the schistosomiasis control programme were collected through different departments of Erhai County government since 2015. System modelling was performed using system dynamics software to establish a simulation model in order to evaluate the effectiveness of intervention activities. RESULTS Ecological approaches to control schistosomiasis in Eryuan County consist of three major components: (i) implementing precise interventions to stop schistosomiasis transmission by means of controlling the source of infection, blocking the biological transmission chains and cutting off the route of disease transmission; (ii) employing ecological approaches to improve the co-effectiveness of environmental protection and schistosomiasis prevention in the study area; and (iii) strengthening the professional skills of personnel involving in the schistosomiasis control programme. Simulation results showed that this strategy could speed up the progress of schistosomiasis control programme moving from the control stage to the elimination stage. CONCLUSIONS Ecological approaches implemented in schistosomiasis endemic areas of the Eryuan region are able to improve the co-effectiveness of environmental protection and schistosomiasis control, providing a new avenue for eliminating schistosomiasis thanks to the application of precise interventions.
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Affiliation(s)
- Yi Dong
- Yunnan Institute of Endemic Diseases Control and Prevention, Dali, 671000, Yunnan, China
| | - Chun-Hong Du
- Yunnan Institute of Endemic Diseases Control and Prevention, Dali, 671000, Yunnan, China
| | - Yun Zhang
- Yunnan Institute of Endemic Diseases Control and Prevention, Dali, 671000, Yunnan, China
| | - Li-Fang Wang
- Yunnan Institute of Endemic Diseases Control and Prevention, Dali, 671000, Yunnan, China
| | - Jing Song
- Yunnan Institute of Endemic Diseases Control and Prevention, Dali, 671000, Yunnan, China
| | - Ming-Shou Wu
- Yunnan Institute of Endemic Diseases Control and Prevention, Dali, 671000, Yunnan, China
| | - Wen-Can Yang
- Eryuan Station of Schistosomiasis Control and Prevention, Eryuan, 671200, Yunnan, China
| | - Shan Lv
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, China.,Chinese Center for Tropical Diseases Research, Shanghai, 200025, China.,WHO Collaborating Centre for Tropical Diseases, Shanghai, 200025, China.,National Center for International Research on Tropical Diseases, Ministry of Science and Technology, Shanghai, 200025, China.,Key Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai, 200025, China
| | - Xiao-Nong Zhou
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, China. .,Chinese Center for Tropical Diseases Research, Shanghai, 200025, China. .,WHO Collaborating Centre for Tropical Diseases, Shanghai, 200025, China. .,National Center for International Research on Tropical Diseases, Ministry of Science and Technology, Shanghai, 200025, China. .,Key Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai, 200025, China.
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3
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Arakala A, Hoover CM, Marshall JM, Sokolow SH, De Leo GA, Rohr JR, Remais JV, Gambhir M. Estimating the elimination feasibility in the 'end game' of control efforts for parasites subjected to regular mass drug administration: Methods and their application to schistosomiasis. PLoS Negl Trop Dis 2018; 12:e0006794. [PMID: 30418968 PMCID: PMC6258430 DOI: 10.1371/journal.pntd.0006794] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Revised: 11/26/2018] [Accepted: 08/27/2018] [Indexed: 11/18/2022] Open
Abstract
Progress towards controlling and eliminating parasitic worms, including schistosomiasis, onchocerciasis, and lymphatic filariasis, is advancing rapidly as national governments, multinational NGOs, and pharmaceutical companies launch collaborative chemotherapeutic control campaigns. Critical questions remain regarding the potential for achieving elimination of these infections, and analytical methods can help to quickly estimate progress towards-and the probability of achieving-elimination over specific timeframes. Here, we propose the effective reproduction number, Reff, as a proxy of elimination potential for sexually reproducing worms that are subject to poor mating success at very low abundance (positive density dependence, or Allee effects). Reff is the number of parasites produced by a single reproductive parasite at a given stage in the transmission cycle, over the parasite's lifetime-it is the generalized form of the more familiar basic reproduction number, R0, which only applies at the beginning of an epidemic-and it can be estimated in a 'model-free' manner by an estimator ('ε'). We introduce ε, demonstrate its estimation using simulated data, and discuss how it may be used in planning and evaluation of ongoing elimination efforts for a range of parasitic diseases.
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Affiliation(s)
- Arathi Arakala
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia
| | - Christopher M. Hoover
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California, United States of America
| | - John M. Marshall
- Division of Epidemiology and Biostatistics, School of Public Health, University of California, Berkeley, California, United States of America
| | - Susanne H. Sokolow
- Department of Biology—Hopkins Marine Station, Stanford University, Pacific Grove, California, United States of America
| | - Giulio A. De Leo
- Department of Biology—Hopkins Marine Station, Stanford University, Pacific Grove, California, United States of America
| | - Jason R. Rohr
- Department of Integrative Biology, University of Southern Florida, Tampa, Florida, United States of America
| | - Justin V. Remais
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California, United States of America
| | - Manoj Gambhir
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia
- Health Modelling and Analytics, IBM Research Australia, Melbourne, Australia
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4
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Yang Y, Zheng SB, Yang Y, Cheng WT, Pan X, Dai QQ, Chen Y, Zhu L, Jiang QW, Zhou YB. The Three Gorges Dam: Does the Flooding Time Determine the Distribution of Schistosome-Transmitting Snails in the Middle and Lower Reaches of the Yangtze River, China? INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2018; 15:E1304. [PMID: 29933638 PMCID: PMC6069228 DOI: 10.3390/ijerph15071304] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Revised: 06/17/2018] [Accepted: 06/18/2018] [Indexed: 11/16/2022]
Abstract
BACKGROUND Schistosomiasis is one of the most devastating tropical diseases in the world. Oncomelania hupensis is the only intermediate host of Schistosoma japonicum, and its growth and development are sensitive to environmental factors. The Three Gorges Dam has substantially altered the water level in the Yangtze River. This study focused on the impact of the flooding time on the occurrence of Oncomelania snails in Hunan Province, China. METHODS The data regarding Oncomelania snails were collected from the Schistosomiasis Atlas of the People's Republic of China. Air temperature, hours of daylight and relative humidity from 1995 to 2002 were collected from the China Meteorological Data Sharing Service System. The data for rainfall and days inundated with water were collected from the Hunan flood control information system and hydrological stations in Hunan Province. A generalized additive model was used to estimate the impact of these factors on the presence or absence of snails. RESULTS The number of days inundated with water in the areas with snails ranged from 56 to 212 days. However, 82 percent of the areas without snails were inundated with water less than 60 days. The lowest air temperature in a year in the areas without snails ranges from -2.88 °C to -2.10 °C, and the range was from -2.88 °C to -2.34 °C for areas with snails. Annual rainfall in the areas with snails ranged from 989 to 1565 mm, and the range was from 1230 mm to 1647 mm for the areas without snails. The results from the generalized additive model showed that the number of days inundated with water, lowest air temperature in a year, annual rainfall, days of daily rainfall greater than 0.1 mm, and hours of daylight were the factors that significantly affect the occurrence of snails in Hunan Province, China. CONCLUSIONS The number of days inundated with water may be a key factor determining the geographical distribution of Oncomelania snails in Hunan Province and the favorable number of days inundated with water for the survival of snails ranges from about 2 to 7 months.
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Affiliation(s)
- Yu Yang
- Fudan University School of Public Health, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
- Key Laboratory of Public Health Safety, Fudan University, Ministry of Education, Building 8, 130 Dong An Road, Xuhui District, Shanghai 200032, China.
- Fudan University Center for Tropical Disease Research, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
| | - Sheng-Bang Zheng
- Fudan University School of Public Health, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
- Key Laboratory of Public Health Safety, Fudan University, Ministry of Education, Building 8, 130 Dong An Road, Xuhui District, Shanghai 200032, China.
- Fudan University Center for Tropical Disease Research, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
| | - Ya Yang
- Fudan University School of Public Health, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
- Key Laboratory of Public Health Safety, Fudan University, Ministry of Education, Building 8, 130 Dong An Road, Xuhui District, Shanghai 200032, China.
- Fudan University Center for Tropical Disease Research, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
| | - Wan-Ting Cheng
- Fudan University School of Public Health, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
- Key Laboratory of Public Health Safety, Fudan University, Ministry of Education, Building 8, 130 Dong An Road, Xuhui District, Shanghai 200032, China.
- Fudan University Center for Tropical Disease Research, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
| | - Xiang Pan
- Fudan University School of Public Health, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
- Key Laboratory of Public Health Safety, Fudan University, Ministry of Education, Building 8, 130 Dong An Road, Xuhui District, Shanghai 200032, China.
- Fudan University Center for Tropical Disease Research, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
| | - Qing-Qing Dai
- Department of Statistics, Oklahoma State University, Stillwater, WA 74078, USA.
| | - Yue Chen
- School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, 600 Peter Morand Crescent, Ottawa, ON K1G 5Z3, Canada.
| | - Lan Zhu
- Department of Statistics, Oklahoma State University, Stillwater, WA 74078, USA.
| | - Qing-Wu Jiang
- Fudan University School of Public Health, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
- Key Laboratory of Public Health Safety, Fudan University, Ministry of Education, Building 8, 130 Dong An Road, Xuhui District, Shanghai 200032, China.
- Fudan University Center for Tropical Disease Research, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
| | - Yi-Biao Zhou
- Fudan University School of Public Health, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
- Key Laboratory of Public Health Safety, Fudan University, Ministry of Education, Building 8, 130 Dong An Road, Xuhui District, Shanghai 200032, China.
- Fudan University Center for Tropical Disease Research, Building 8, 130 Dong'an Road, Xuhui District, Shanghai 200032, China.
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Liang L, Gong P. Climate change and human infectious diseases: A synthesis of research findings from global and spatio-temporal perspectives. ENVIRONMENT INTERNATIONAL 2017; 103:99-108. [PMID: 28342661 DOI: 10.1016/j.envint.2017.03.011] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Revised: 02/22/2017] [Accepted: 03/15/2017] [Indexed: 06/06/2023]
Abstract
The life cycles and transmission of most infectious agents are inextricably linked with climate. In spite of a growing level of interest and progress in determining climate change effects on infectious disease, the debate on the potential health outcomes remains polarizing, which is partly attributable to the varying effects of climate change, different types of pathogen-host systems, and spatio-temporal scales. We summarize the published evidence and show that over the past few decades, the reported negative or uncertain responses of infectious diseases to climate change has been growing. A feature of the research tendency is the focus on temperature and insect-borne diseases at the local and decadal scale. Geographically, regions experiencing higher temperature anomalies have been given more research attention; unfortunately, the Earth's most vulnerable regions to climate variability and extreme events have been less studied. From local to global scales, agreements on the response of infectious diseases to climate change tend to converge. So far, an abundance of findings have been based on statistical methods, with the number of mechanistic studies slowly growing. Research gaps and trends identified in this study should be addressed in the future.
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Affiliation(s)
- Lu Liang
- Arkansas Forest Resources Center, University of Arkansas Division of Agriculture, School of Forestry and Natural Resources, University of Arkansas at Monticello, Monticello, 110 University Court, AR 71656, USA; Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA.
| | - Peng Gong
- Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA; Ministry of Education Key Laboratory for Earth System Modeling, Department of Earth System Science, Tsinghua University, Beijing 100084, China
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6
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Head JR, Chang H, Li Q, Hoover CM, Wilke T, Clewing C, Carlton EJ, Liang S, Lu D, Zhong B, Remais JV. Genetic Evidence of Contemporary Dispersal of the Intermediate Snail Host of Schistosoma japonicum: Movement of an NTD Host Is Facilitated by Land Use and Landscape Connectivity. PLoS Negl Trop Dis 2016; 10:e0005151. [PMID: 27977674 PMCID: PMC5157946 DOI: 10.1371/journal.pntd.0005151] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 11/01/2016] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND While the dispersal of hosts and vectors-through active or passive movement-is known to facilitate the spread and re-emergence of certain infectious diseases, little is known about the movement ecology of Oncomelania spp., intermediate snail host of the parasite Schistosoma japonicum, and its consequences for the spread of schistosomiasis in East and Southeast Asia. In China, despite intense control programs aimed at preventing schistosomiasis transmission, there is evidence in recent years of re-emergence and persistence of infection in some areas, as well as an increase in the spatial extent of the snail host. A quantitative understanding of the dispersal characteristics of the intermediate host can provide new insights into the spatial dynamics of transmission, and can assist public health officials in limiting the geographic spread of infection. METHODOLOGY/PRINCIPAL FINDINGS Oncomelania hupensis robertsoni snails (n = 833) were sampled from 29 sites in Sichuan, China, genotyped, and analyzed using Bayesian assignment to estimate the rate of recent snail migration across sites. Landscape connectivity between each site pair was estimated using the geographic distance distributions derived from nine environmental models: Euclidean, topography, incline, wetness, land use, watershed, stream use, streams and channels, and stream velocity. Among sites, 14.4% to 32.8% of sampled snails were identified as recent migrants, with 20 sites comprising >20% migrants. Migration rates were generally low between sites, but at 8 sites, over 10% of the overall host population originated from one proximal site. Greater landscape connectivity was significantly associated with increased odds of migration, with the minimum path distance (as opposed to median or first quartile) emerging as the strongest predictor across all environmental models. Models accounting for land use explained the largest proportion of the variance in migration rates between sites. A greater number of irrigation channels leading into a site was associated with an increase in the site's propensity to both attract and retain snails. CONCLUSIONS/SIGNIFICANCE Our findings have important implications for controlling the geographic spread of schistosomiasis in China, through improved understanding of the dispersal capacity of the parasite's intermediate host.
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Affiliation(s)
- Jennifer R. Head
- Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, Georgia, United States of America
| | - Howard Chang
- Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, Georgia, United States of America
| | - Qunna Li
- Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, Georgia, United States of America
| | - Christopher M. Hoover
- Environmental Health Sciences, School of Public Health, University of California, Berkeley, California, United States of America
| | - Thomas Wilke
- Department of Animal Ecology and Systematics, Justus Liebig University, Giessen, Germany
| | - Catharina Clewing
- Department of Animal Ecology and Systematics, Justus Liebig University, Giessen, Germany
| | - Elizabeth J. Carlton
- Department of Environmental and Occupational Health, Colorado School of Public Health, University of Colorado, Anschutz, Aurora, Colorado, United States of America
| | - Song Liang
- Department of Environmental & Global Health, College of Public Health and Health Professions, University of Florida, Gainesville, Florida, United States of America
| | - Ding Lu
- Institute of Parasitic Diseases, Sichuan Center for Disease Control and Prevention, Chengdu, China
| | - Bo Zhong
- Institute of Parasitic Diseases, Sichuan Center for Disease Control and Prevention, Chengdu, China
| | - Justin V. Remais
- Environmental Health Sciences, School of Public Health, University of California, Berkeley, California, United States of America
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Hydrology and density feedbacks control the ecology of intermediate hosts of schistosomiasis across habitats in seasonal climates. Proc Natl Acad Sci U S A 2016; 113:6427-32. [PMID: 27162339 DOI: 10.1073/pnas.1602251113] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We report about field and theoretical studies on the ecology of the aquatic snails (Bulinus spp. and Biomphalaria pfeifferi) that serve as obligate intermediate hosts in the complex life cycle of the parasites causing human schistosomiasis. Snail abundance fosters disease transmission, and thus the dynamics of snail populations are critically important for schistosomiasis modeling and control. Here, we single out hydrological drivers and density dependence (or lack of it) of ecological growth rates of local snail populations by contrasting novel ecological and environmental data with various models of host demography. Specifically, we study various natural and man-made habitats across Burkina Faso's highly seasonal climatic zones. Demographic models are ranked through formal model comparison and structural risk minimization. The latter allows us to evaluate the suitability of population models while clarifying the relevant covariates that explain empirical observations of snail abundance under the actual climatic forcings experienced by the various field sites. Our results link quantitatively hydrological drivers to distinct population dynamics through specific density feedbacks, and show that statistical methods based on model averaging provide reliable snail abundance projections. The consistency of our ranking results suggests the use of ad hoc models of snail demography depending on habitat type (e.g., natural vs. man-made) and hydrological characteristics (e.g., ephemeral vs. permanent). Implications for risk mapping and space-time allocation of control measures in schistosomiasis-endemic contexts are discussed.
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Feng Y, Liu L, Xia S, Xu JF, Bergquist R, Yang GJ. Reaching the Surveillance-Response Stage of Schistosomiasis Control in The People's Republic of China: A Modelling Approach. ADVANCES IN PARASITOLOGY 2016; 92:165-96. [PMID: 27137447 DOI: 10.1016/bs.apar.2016.02.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
With the goal set to eliminate schistosomiasis nationwide by 2020, The People's Republic of China has initiated the surveillance-response stage to identify remaining sources of infection and potential pockets from where the disease could reemerge. Shifting the focus from classical monitoring and evaluation to rapid detection and immediate response, this approach requires modelling to bridge the surveillance and response components. We review here studies relevant to schistosomiasis modelling in a Chinese surveillance-response system with the expectation to achieve a practically useful understanding of the current situation and potential future study directions. We also present useful experience that could tentatively be applied in other endemic regions in the world. Modelling is discussed at length as it plays an essential role, both with regard to the intermediate snail host and in the definitive, mammal hosts. Research gaps with respect to snail infection, animal hosts and sectoral research cooperation are identified and examined against the prevailing background of ecosystem and socioeconomic changes with a focus on coexisting challenges and opportunities in a situation with increasing financial constraints.
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Affiliation(s)
- Y Feng
- Key Laboratory of National Health and Family Planning Commission on Parasitic Disease Control and Prevention, Jiangsu Provincial Key Laboratory on Parasite and Vector Control Technology, Wuxi, The People's Republic of China; Jiangsu Institute of Parasitic Diseases, Wuxi, Jiangsu Province, The People's Republic of China; Jiangsu Provincial Key Laboratory of Parasite Molecular Biology, Wuxi, The People's Republic of China; Public Health Research Center, Jiangnan University, Wuxi, Jiangsu Province, The People's Republic of China
| | - L Liu
- Key Laboratory of National Health and Family Planning Commission on Parasitic Disease Control and Prevention, Jiangsu Provincial Key Laboratory on Parasite and Vector Control Technology, Wuxi, The People's Republic of China; Jiangsu Institute of Parasitic Diseases, Wuxi, Jiangsu Province, The People's Republic of China; Jiangsu Provincial Key Laboratory of Parasite Molecular Biology, Wuxi, The People's Republic of China; Public Health Research Center, Jiangnan University, Wuxi, Jiangsu Province, The People's Republic of China
| | - S Xia
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, The People's Republic of China; Key Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai, The People's Republic of China; WHO Collaborating Center for Tropical Diseases, Shanghai, The People's Republic of China
| | - J-F Xu
- Hubei University for Nationalities, The People's Republic of China
| | - R Bergquist
- Geospatial Health, University of Naples Federico II, Naples, Italy
| | - G-J Yang
- Key Laboratory of National Health and Family Planning Commission on Parasitic Disease Control and Prevention, Jiangsu Provincial Key Laboratory on Parasite and Vector Control Technology, Wuxi, The People's Republic of China; Jiangsu Institute of Parasitic Diseases, Wuxi, Jiangsu Province, The People's Republic of China; Jiangsu Provincial Key Laboratory of Parasite Molecular Biology, Wuxi, The People's Republic of China; Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland
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9
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Wetlands explain most in the genetic divergence pattern of Oncomelania hupensis. INFECTION GENETICS AND EVOLUTION 2014; 27:436-44. [PMID: 25183028 DOI: 10.1016/j.meegid.2014.08.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Revised: 08/10/2014] [Accepted: 08/15/2014] [Indexed: 11/22/2022]
Abstract
Understanding the divergence patterns of hosts could shed lights on the prediction of their parasite transmission. No effort has been devoted to understand the drivers of genetic divergence pattern of Oncomelania hupensis, the only intermediate host of Schistosoma japonicum. Based on a compilation of two O. hupensis gene datasets covering a wide geographic range in China and an array of geographical distance and environmental dissimilarity metrics built from earth observation data and ecological niche modeling, we conducted causal modeling analysis via simple, partial Mantel test and local polynomial fitting to understand the interactions among isolation-by-distance, isolation-by-environment, and genetic divergence. We found that geography contributes more to genetic divergence than environmental isolation, and among all variables involved, wetland showed the strongest correlation with the genetic pairwise distances. These results suggested that in China, O. hupensis dispersal is strongly linked to the distribution of wetlands, and the current divergence pattern of both O. hupensis and schistosomiasis might be altered due to the changed wetland pattern with the accomplishment of the Three Gorges Dam and the South-to-North water transfer project.
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10
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Moore JL, Remais JV. Developmental models for estimating ecological responses to environmental variability: structural, parametric, and experimental issues. Acta Biotheor 2014; 62:69-90. [PMID: 24443079 DOI: 10.1007/s10441-014-9209-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Accepted: 01/07/2014] [Indexed: 10/25/2022]
Abstract
Developmental models that account for the metabolic effect of temperature variability on poikilotherms, such as degree-day models, have been widely used to study organism emergence, range and development, particularly in agricultural and vector-borne disease contexts. Though simple and easy to use, structural and parametric issues can influence the outputs of such models, often substantially. Because the underlying assumptions and limitations of these models have rarely been considered, this paper reviews the structural, parametric, and experimental issues that arise when using degree-day models, including the implications of particular structural or parametric choices, as well as assumptions that underlie commonly used models. Linear and non-linear developmental functions are compared, as are common methods used to incorporate temperature thresholds and calculate daily degree-days. Substantial differences in predicted emergence time arose when using linear versus non-linear developmental functions to model the emergence time in a model organism. The optimal method for calculating degree-days depends upon where key temperature threshold parameters fall relative to the daily minimum and maximum temperatures, as well as the shape of the daily temperature curve. No method is shown to be universally superior, though one commonly used method, the daily average method, consistently provides accurate results. The sensitivity of model projections to these methodological issues highlights the need to make structural and parametric selections based on a careful consideration of the specific biological response of the organism under study, and the specific temperature conditions of the geographic regions of interest. When degree-day model limitations are considered and model assumptions met, the models can be a powerful tool for studying temperature-dependent development.
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Moore JL, Liang S, Akullian A, Remais JV. Cautioning the use of degree-day models for climate change projections in the presence of parametric uncertainty. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2012; 22:2237-2247. [PMID: 23387122 PMCID: PMC3816756 DOI: 10.1890/12-0127.1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Developmental models, such as degree-day models, are commonly used to predict the impact of future climate change on the intensity, distribution, and timing of the transmission of infectious diseases, particularly those caused by pathogens carried by vectors or intermediate hosts. Resulting projections can be useful in policy discussions concerning regional or national responses to future distributions of important infectious diseases. Although the simplicity of degree-day models is appealing, little work has been done to analyze their ability to make reliable projections of the distribution of important pathogens, vectors, or intermediate hosts in the presence of the often considerable parametric uncertainty common to such models. Here, a population model of Oncomelania hupensis, the intermediate host of Schistosoma japonicum, was used to investigate the sensitivity of host range predictions in Sichuan Province, China, to uncertainty in two key degree-day model parameters: delta(min) (minimum temperature threshold for development) and K (total degree-days required for completion of snail development). The intent was to examine the consequences of parametric uncertainty in a plausible biological model, rather than to generate the definitive model. Results indicate that model output, the seasonality of population dynamics, and range predictions, particularly along the edge of the range, are highly sensitive to changes in model parameters, even at levels of parametric uncertainty common to such applications. Caution should be used when interpreting the results of degree-day models used to generate predictions of disease distribution and risk under scenarios of future climate change, and predictions should be considered most reliable when the temperature ranges used in projections resemble those used to estimate model parameters. Given the potential for substantial changes in degree-day model output with modest changes in parameter values, caution is warranted when results will be used to inform policy and management decisions.
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Affiliation(s)
- Julia L Moore
- Program in Population Biology, Ecology and Evolution, Graduate Division of Biological and Biomedical Sciences, Emory University, 1510 Clifton Rd, Atlanta, GA 30322, USA
| | - Song Liang
- Department of Environmental and Global Health, College of Public Health & Health Professions, and Emerging Pathogens Institute, University of Florida, PO Box 100188, Gainesville, FL 32610, USA
| | - Adam Akullian
- Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Box 357236, Seattle, WA 98195, USA
| | - Justin V Remais
- Program in Population Biology, Ecology and Evolution, Graduate Division of Biological and Biomedical Sciences, Emory University, 1510 Clifton Rd, Atlanta, GA 30322, USA
- Department of Environmental Health, Rollins School of Public Health, Emory University, 1518 Clifton Rd Room 2023, Atlanta, GA 30322, USA. Tel.: +1 404 712 8908; Fax: +1 404 727 8744
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Akullian AN, Lu D, McDowell JZ, Davis GM, Spear RC, Remais JV. Modeling the combined influence of host dispersal and waterborne fate and transport on pathogen spread in complex landscapes. WATER QUALITY, EXPOSURE, AND HEALTH 2012; 4:159-168. [PMID: 23162675 PMCID: PMC3496273 DOI: 10.1007/s12403-012-0074-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Environmental models, often applied to questions on the fate and transport of chemical hazards, have recently become important in tracing certain environmental pathogens to their upstream sources of contamination. These tools, such as first order decay models applied to contaminants in surface waters, offer promise for quantifying the fate and transport of pathogens with multiple environmental stages and/or multiple hosts, in addition to those pathogens whose environmental stages are entirely waterborne. Here we consider the fate and transport capabilities of the human schistosome Schistosoma japonicum, which exhibits two waterborne stages and is carried by an amphibious intermediate snail host. We present experimentally-derived dispersal estimates for the intermediate snail host and fate and transport estimates for the passive downstream diffusion of cercariae, the waterborne, human-infective parasite stage. Using a one dimensional advective transport model exhibiting first-order decay, we simulate the added spatial reach and relative increase in cercarial concentrations that dispersing snail hosts contribute to downstream sites. Simulation results suggest that snail dispersal can substantially increase the concentrations of cercariae reaching downstream locations, relative to no snail dispersal, effectively putting otherwise isolated downstream sites at increased risk of exposure to cercariae from upstream sources. The models developed here can be applied to other infectious diseases with multiple life-stages and hosts, and have important implications for targeted ecological control of disease spread.
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Affiliation(s)
- Adam N. Akullian
- University of Washington, School of Public Health and Community Medicine, Department of Epidemiology, Box 357236, Seattle, WA 98195, USA, Tel.: +1 206 897 6396
| | - Ding Lu
- Institute of Parasitic Disease, Sichuan Provincial Center for Disease Control and Prevention, 6 ZhongXue Road, Chengdu 610041, Sichuan, People’s Republic of China
| | - Julia Z. McDowell
- Department of Environmental Health, Rollins School of Public Health, Emory University, 1518 Clifton Rd Room 2023, Atlanta, GA 30322, USA. Tel.: +1 404 712 8908
| | - George M. Davis
- Department of Microbiology and Tropical Medicine, George Washington University Medical Center, 745 Ross Hall, 2300 Eye St., N. W., Washington, D. C. 20037
| | - Robert C. Spear
- Center for Occupational and Environmental Health, School of Public Health, University of California, Berkeley, 50 University Hall, Berkeley, CA 94720-7360, USA. Tel.: +1 510 642 0761
| | - Justin V. Remais
- Department of Environmental Health, Rollins School of Public Health, Emory University, 1518 Clifton Rd Room 2023, Atlanta, GA 30322, USA. Tel.: +1 404 712 8908
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Emmanuel NN, Loha N, Okolo MO, Ikenna OK. Landscape epidemiology: An emerging perspective in the mapping and modelling of disease and disease risk factors. ASIAN PACIFIC JOURNAL OF TROPICAL DISEASE 2011. [DOI: 10.1016/s2222-1808(11)60041-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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Model approaches for estimating the influence of time-varying socio-environmental factors on macroparasite transmission in two endemic regions. Epidemics 2011; 1:213-20. [PMID: 20454601 DOI: 10.1016/j.epidem.2009.10.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The environmental determinants of vector- and host-borne diseases include time-varying components that modify key transmission parameters, resulting in transient couplings between environmental phenomena and transmission processes. While some time-varying drivers are periodic in nature, some are aperiodic, such as those that involve episodic events or complex patterns of human behavior. Understanding these couplings can allow for prediction of periods of peak infection risk, and ultimately presents opportunities for optimizing intervention selection and timing. Schistosome macroparasites of humans exhibit multiple free-living stages as well as intermediate hosts, and are thus model organisms for illustrating the influence of environmental forcing on transmission. Time-varying environmental factors, termed gating functions, for schistosomes include larval response to temperature and rainfall, seasonal water contact patterns and snail population dynamics driven by weather variables. The biological bases for these modifiers are reviewed, and their values are estimated and incorporated into a transmission model that simulates a multi-year period in two schistosomiasis endemic regions. Modeling results combined with a scale dependent correlation analysis indicate the end effect of these site-specific gating functions is to strongly govern worm burden in these communities, in a manner particularly sensitive to the hydrological differences between sites. Two classes of gating functions were identified, those that act in concert to modify human infection (and determine worm acquisition late in the season), and those that act on snail infection (and determine early season worm acquisition). The importance of these factors for control programs and surveillance is discussed.
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Remais J. Modelling environmentally-mediated infectious diseases of humans: transmission dynamics of schistosomiasis in China. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 673:79-98. [PMID: 20632531 PMCID: PMC7123861 DOI: 10.1007/978-1-4419-6064-1_6] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
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.
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Affiliation(s)
- Justin Remais
- Rollins School of Public Health, Department of Environmental and Occupational Health, Emory University, Atlanta, Georgia, USA.
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Sudat SEK, Carlton EJ, Seto EYW, Spear RC, Hubbard AE. Using variable importance measures from causal inference to rank risk factors of schistosomiasis infection in a rural setting in China. EPIDEMIOLOGIC PERSPECTIVES & INNOVATIONS : EP+I 2010; 7:3. [PMID: 20626918 PMCID: PMC2913928 DOI: 10.1186/1742-5573-7-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/18/2009] [Accepted: 07/14/2010] [Indexed: 12/03/2022]
Abstract
BACKGROUND Schistosomiasis infection, contracted through contact with contaminated water, is a global public health concern. In this paper we analyze data from a retrospective study reporting water contact and schistosomiasis infection status among 1011 individuals in rural China. We present semi-parametric methods for identifying risk factors through a comparison of three analysis approaches: a prediction-focused machine learning algorithm, a simple main-effects multivariable regression, and a semi-parametric variable importance (VI) estimate inspired by a causal population intervention parameter. RESULTS The multivariable regression found only tool washing to be associated with the outcome, with a relative risk of 1.03 and a 95% confidence interval (CI) of 1.01-1.05. Three types of water contact were found to be associated with the outcome in the semi-parametric VI analysis: July water contact (VI estimate 0.16, 95% CI 0.11-0.22), water contact from tool washing (VI estimate 0.88, 95% CI 0.80-0.97), and water contact from rice planting (VI estimate 0.71, 95% CI 0.53-0.96). The July VI result, in particular, indicated a strong association with infection status - its causal interpretation implies that eliminating water contact in July would reduce the prevalence of schistosomiasis in our study population by 84%, or from 0.3 to 0.05 (95% CI 78%-89%). CONCLUSIONS The July VI estimate suggests possible within-season variability in schistosomiasis infection risk, an association not detected by the regression analysis. Though there are many limitations to this study that temper the potential for causal interpretations, if a high-risk time period could be detected in something close to real time, new prevention options would be opened. Most importantly, we emphasize that traditional regression approaches are usually based on arbitrary pre-specified models, making their parameters difficult to interpret in the context of real-world applications. Our results support the practical application of analysis approaches that, in contrast, do not require arbitrary model pre-specification, estimate parameters that have simple public health interpretations, and apply inference that considers model selection as a source of variation.
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Affiliation(s)
- Sylvia EK Sudat
- Division of Biostatistics, University of California, Berkeley, USA
| | - Elizabeth J Carlton
- Department of Environmental Health Sciences, University of California, Berkeley, USA
| | - Edmund YW Seto
- Department of Environmental Health Sciences, University of California, Berkeley, USA
| | - Robert C Spear
- Department of Environmental Health Sciences, University of California, Berkeley, USA
| | - Alan E Hubbard
- Division of Biostatistics, University of California, Berkeley, USA
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Remais J, Akullian A, Ding L, Seto E. Analytical methods for quantifying environmental connectivity for the control and surveillance of infectious disease spread. J R Soc Interface 2010; 7:1181-93. [PMID: 20164085 DOI: 10.1098/rsif.2009.0523] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The sustained transmission and spread of environmentally mediated infectious diseases is governed in part by the dispersal of parasites, disease vectors and intermediate hosts between sites of transmission. Functional geospatial models can be used to quantify and predict the degree to which environmental features facilitate or limit connectivity between target populations, yet typical models are limited in their geographical and analytical approach, providing simplistic, global measures of connectivity and lacking methods to assess the epidemiological implications of fine-scale heterogeneous landscapes. Here, functional spatial models are applied to problems of surveillance and control of the parasitic blood fluke Schistosoma japonicum and its intermediate snail host Oncomelania haupensis in western China. We advance functional connectivity methods by providing an analytical framework to (i) identify nodes of transmission where the degree of connectedness to other villages, and thus the potential for disease spread, is higher than is estimated using Euclidean distance alone and (ii) (re)organize transmission sites into disease surveillance units based on second-order relationships among nodes using non-Euclidean distance measures, termed effective geographical distance (EGD). Functional environmental models are parametrized using ecological information on the target organisms, and pair-wise distributions of inter-node EGD are estimated. A Monte Carlo rank product analysis is presented to identify nearby nodes under alternative distance models. Nodes are then iteratively embedded into EGD space and clustered using a k-means algorithm to group villages into ecologically meaningful surveillance groups. A consensus clustering approach is taken to derive the most stable cluster structure. The results indicate that novel relationships between nodes are revealed when non-Euclidean, ecologically determined distance measures are used to quantify connectivity in heterogeneous landscapes. These connections are not evident when analysing nodes in Euclidean space, and thus surveillance and control activities planned using Euclidean distance measures may be suboptimal. The methods developed here provide a quantitative framework for assessing the effectiveness of ecologically grounded surveillance systems and of control and prevention strategies for environmentally mediated diseases.
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Affiliation(s)
- Justin Remais
- Department of Environmental Health, Rollins School of Public Health, Emory University, 1518 Clifton Road NE, Atlanta, GA 30322, USA.
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Remais J, Liang S, Spear RC. Coupling hydrologic and infectious disease models to explain regional differences in schistosomiasis transmission in southwestern China. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2008; 42:2643-2649. [PMID: 18505010 DOI: 10.1021/es071052s] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Rainfall-runoff models have become essential tools for conceptualizing and predicting the response of hydrologic processes to changing environments, but they have rarely been applied to challenges facing health scientists. Yet with their efficient parameterization and modest data requirements, they hold great promise for epidemiological application. A modeling analysis incorporating simple hydrologic constraints on transmission of the human parasite Schistosoma japonicum in southwestern China was conducted by coupling a lumped parameter rainfall-runoff model (IHACRES) with a delay-differential equation schistosomiasis transmission model modified to account for channel flows and on-field egg inactivation. Model predictions of prevalence and infection timing agree with observations in the region, which indicate that hydrological differences between sites can lead to pronounced differences in transmission. Channel flows are shown to be important in determining infection intensity and timing in modeled village populations. In the periodic absence of flow, overall transmission intensity is reduced among all modeled risk groups. However, the influence of hydrologic variability was greater on the cercarial stage of the parasite than the miracidial stage, due to the parasite ova's ability to survive dormant on fields between rain events. The predictive power gained from including hydrological data in epidemiological models can improve risk assessments for environmentally mediated diseases, under both long-term climate change scenarios and near-term weather fluctuations.
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Affiliation(s)
- Justin Remais
- Center for Occupational and Environmental Health, School of Public Health, 50 University Hall, University of California, Berkeley, Berkeley, California 94720-7360, USA.
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