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Reitzug F, Ledien J, Chami GF. Associations of water contact frequency, duration, and activities with schistosome infection risk: A systematic review and meta-analysis. PLoS Negl Trop Dis 2023; 17:e0011377. [PMID: 37315020 DOI: 10.1371/journal.pntd.0011377] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Accepted: 05/12/2023] [Indexed: 06/16/2023] Open
Abstract
BACKGROUND Schistosomiasis is a water-borne parasitic disease which affects over 230 million people globally. The relationship between contact with open freshwater bodies and the likelihood of schistosome infection remains poorly quantified despite its importance for understanding transmission and parametrising transmission models. METHODS We conducted a systematic review to estimate the average effect of water contact duration, frequency, and activities on schistosome infection likelihood. We searched Embase, MEDLINE (including PubMed), Global Health, Global Index Medicus, Web of Science, and the Cochrane Central Register of Controlled Trials from inception until May 13, 2022. Observational and interventional studies reporting odds ratios (OR), hazard ratios (HR), or sufficient information to reconstruct effect sizes on individual-level associations between water contact and infection with any Schistosoma species were eligible for inclusion. Random-effects meta-analysis with inverse variance weighting was used to calculate pooled ORs and 95% confidence intervals (CIs). RESULTS We screened 1,411 studies and included 101 studies which represented 192,691 participants across Africa, Asia, and South America. Included studies mostly reported on water contact activities (69%; 70/101) and having any water contact (33%; 33/101). Ninety-six percent of studies (97/101) used surveys to measure exposure. A meta-analysis of 33 studies showed that individuals with water contact were 3.14 times more likely to be infected (OR 3.14; 95% CI: 2.08-4.75) when compared to individuals with no water contact. Subgroup analyses showed that the positive association of water contact with infection was significantly weaker in children compared to studies which included adults and children (OR 1.67; 95% CI: 1.04-2.69 vs. OR 4.24; 95% CI: 2.59-6.97). An association of water contact with infection was only found in communities with ≥10% schistosome prevalence. Overall heterogeneity was substantial (I2 = 93%) and remained high across all subgroups, except in direct observation studies (I2 range = 44%-98%). We did not find that occupational water contact such as fishing and agriculture (OR 2.57; 95% CI: 1.89-3.51) conferred a significantly higher risk of schistosome infection compared to recreational water contact (OR 2.13; 95% CI: 1.75-2.60) or domestic water contact (OR 1.91; 95% CI: 1.47-2.48). Higher duration or frequency of water contact did not significantly modify infection likelihood. Study quality across analyses was largely moderate or poor. CONCLUSIONS Any current water contact was robustly associated with schistosome infection status, and this relationship held across adults and children, and schistosomiasis-endemic areas with prevalence greater than 10%. Substantial gaps remain in published studies for understanding interactions of water contact with age and gender, and the influence of these interactions for infection likelihood. As such, more empirical studies are needed to accurately parametrise exposure in transmission models. Our results imply the need for population-wide treatment and prevention strategies in endemic settings as exposure within these communities was not confined to currently prioritised high-risk groups such as fishing populations.
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Affiliation(s)
- Fabian Reitzug
- Big Data Institute, Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom
| | - Julia Ledien
- Big Data Institute, Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom
| | - Goylette F Chami
- Big Data Institute, Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom
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Systematic Review and Meta-Analysis on the Infection Rates of Schistosome Transmitting Snails in Southern Africa. Trop Med Infect Dis 2022; 7:tropicalmed7050072. [PMID: 35622699 PMCID: PMC9145527 DOI: 10.3390/tropicalmed7050072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Revised: 04/21/2022] [Accepted: 04/21/2022] [Indexed: 02/05/2023] Open
Abstract
Efforts to interrupt and eliminate schistosomiasis as a public health problem have increased in several Southern African countries. A systematic review was carried out on the infection rates of snails that cause schistosomiasis in humans. The searches were conducted in PubMed, Web of Science, and Scopus databases, using the PRISMA guidelines from inception to 24 February 2022. The study quality was assessed by using the Joanna Briggs Institute prevalence critical appraisal checklist. Pooled infection rates were estimated by using an inverse variance heterogeneity model, while heterogeneity was determined by using Cochran’s Q test and Higgins i2 statistics. A total of 572 articles were screened, but only 28 studies were eligible for inclusion based on predetermined criteria. In the selected studies, 82,471 Bulinus spp. and 16,784 Biomphalaria spp. snails were screened for cercariae. The pooled infectivity of schistosome intermediate host snails, Biomphalaria spp., and Bulinus spp. were 1%, 2%, and 1%, respectively. Snail infection rates were higher in the 1900s compared to the 2000s. A Luis Furuya–Kanamori index of 3.16 indicated publication bias, and a high level of heterogeneity was observed. Although snail infectivity in Southern Africa is relatively low, it falls within the interval of common snail infection rates, thus indicating the need for suitable snail control programs that could interrupt transmission and achieve elimination.
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Lund AJ, Sokolow SH, Jones IJ, Wood CL, Ali S, Chamberlin A, Sy AB, Sam MM, Jouanard N, Schacht AM, Senghor S, Fall A, Ndione R, Riveau G, De Leo GA, López-Carr D. Exposure, hazard, and vulnerability all contribute to Schistosoma haematobium re-infection in northern Senegal. PLoS Negl Trop Dis 2021; 15:e0009806. [PMID: 34610025 PMCID: PMC8525765 DOI: 10.1371/journal.pntd.0009806] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 10/19/2021] [Accepted: 09/10/2021] [Indexed: 11/19/2022] Open
Abstract
Background Infectious disease risk is driven by three interrelated components: exposure, hazard, and vulnerability. For schistosomiasis, exposure occurs through contact with water, which is often tied to daily activities. Water contact, however, does not imply risk unless the environmental hazard of snails and parasites is also present in the water. By increasing reliance on hazardous activities and environments, socio-economic vulnerability can hinder reductions in exposure to a hazard. We aimed to quantify the contributions of exposure, hazard, and vulnerability to the presence and intensity of Schistosoma haematobium re-infection. Methodology/Principal findings In 13 villages along the Senegal River, we collected parasitological data from 821 school-aged children, survey data from 411 households where those children resided, and ecological data from all 24 village water access sites. We fit mixed-effects logistic and negative binomial regressions with indices of exposure, hazard, and vulnerability as explanatory variables of Schistosoma haematobium presence and intensity, respectively, controlling for demographic variables. Using multi-model inference to calculate the relative importance of each component of risk, we found that hazard (Ʃwi = 0.95) was the most important component of S. haematobium presence, followed by vulnerability (Ʃwi = 0.91). Exposure (Ʃwi = 1.00) was the most important component of S. haematobium intensity, followed by hazard (Ʃwi = 0.77). Model averaging quantified associations between each infection outcome and indices of exposure, hazard, and vulnerability, revealing a positive association between hazard and infection presence (OR = 1.49, 95% CI 1.12, 1.97), and a positive association between exposure and infection intensity (RR 2.59–3.86, depending on the category; all 95% CIs above 1) Conclusions/Significance Our findings underscore the linkages between social (exposure and vulnerability) and environmental (hazard) processes in the acquisition and accumulation of S. haematobium infection. This approach highlights the importance of implementing both social and environmental interventions to complement mass drug administration. While the impacts of natural hazards tend to be described in terms of social determinants such as exposure and vulnerability, the risk for infectious disease is often expressed in terms of environmental determinants without fully considering the socio-ecological processes that put people in contact with infective agents of disease. In the case of schistosomiasis, risk is determined by human interactions with freshwater environments where schistosome parasites circulate between people and aquatic snails. In this study, we quantified the relative contributions of exposure, hazard, and vulnerability to schistosome re-infection among schoolchildren in an endemic region of northern Senegal. We find that hazard and vulnerability influence whether a child becomes infected, while exposure and hazard influence the burden of worms once infection is acquired. Increasing numbers of worms is known to be positively associated with increasing severity of disease. Our findings underscore the importance of evaluating social and environmental determinants of disease simultaneously; omitting measures of exposure, hazard or vulnerability may limit our understanding of risk.
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Affiliation(s)
- Andrea J. Lund
- Emmett Interdisciplinary Program in Environment and Resources, Stanford University, Stanford, California, United States of America
- * E-mail:
| | - Susanne H. Sokolow
- Hopkins Marine Station, Stanford University, Pacific Grove, California, United States of America
- Woods Institute for the Environment, Stanford University, Stanford, California, United States of America
| | - Isabel J. Jones
- Hopkins Marine Station, Stanford University, Pacific Grove, California, United States of America
| | - Chelsea L. Wood
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, United States of America
| | - Sofia Ali
- Stanford University, Stanford, California, United States of America
| | - Andrew Chamberlin
- Hopkins Marine Station, Stanford University, Pacific Grove, California, United States of America
| | - Alioune Badara Sy
- Centre de Recherche Biomédicale–Espoir Pour La Sante, Saint Louis, Sénégal
| | - M. Moustapha Sam
- Centre de Recherche Biomédicale–Espoir Pour La Sante, Saint Louis, Sénégal
| | - Nicolas Jouanard
- Centre de Recherche Biomédicale–Espoir Pour La Sante, Saint Louis, Sénégal
- Station d’Innovation Aquacole, Saint Louis, Sénégal
| | - Anne-Marie Schacht
- Centre de Recherche Biomédicale–Espoir Pour La Sante, Saint Louis, Sénégal
- University of Lille, CNRS, INSERM, CHU Lille, Institut Pasteur de Lille, Center for Infection and Immunity of Lille, Lille, France
| | - Simon Senghor
- Centre de Recherche Biomédicale–Espoir Pour La Sante, Saint Louis, Sénégal
| | - Assane Fall
- Centre de Recherche Biomédicale–Espoir Pour La Sante, Saint Louis, Sénégal
| | - Raphael Ndione
- Centre de Recherche Biomédicale–Espoir Pour La Sante, Saint Louis, Sénégal
| | - Gilles Riveau
- Centre de Recherche Biomédicale–Espoir Pour La Sante, Saint Louis, Sénégal
- University of Lille, CNRS, INSERM, CHU Lille, Institut Pasteur de Lille, Center for Infection and Immunity of Lille, Lille, France
| | - Giulio A. De Leo
- Hopkins Marine Station, Stanford University, Pacific Grove, California, United States of America
- Woods Institute for the Environment, Stanford University, Stanford, California, United States of America
| | - David López-Carr
- Department of Geography, University of California, Santa Barbara, CA, United States of America
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Fukushige M, Chase-Topping M, Woolhouse MEJ, Mutapi F. Efficacy of praziquantel has been maintained over four decades (from 1977 to 2018): A systematic review and meta-analysis of factors influence its efficacy. PLoS Negl Trop Dis 2021; 15:e0009189. [PMID: 33730095 PMCID: PMC7968639 DOI: 10.1371/journal.pntd.0009189] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 02/01/2021] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND The antihelminthic drug praziquantel has been used as the drug of choice for treating schistosome infection for more than 40 years. Although some epidemiological studies have reported low praziquantel efficacy in cure rate (CR) and/or egg reduction rate (ERR), there is no consistent robust evidence of the development of schistosome resistance to praziquantel (PZQ). There is need to determine factors that lead to variable treatment CR and/or ERR. Therefore, we conducted a systematic review and meta-analysis to review CR and ERR as well as identify their predictors. METHODOLOGY/PRINCIPAL FINDINGS In this systematic review and meta-analysis, a literature review was conducted using Biosis Citation Index, Data Citation Index, MEDLINE, and Web of Science Core Collection all of which were provided through Web of Science. Alongside these, EMBASE, and CAB abstracts were searched to identify relevant articles. Random effect meta-regression models were used to identify the factors that influence CR and/or ERR by considering differences in host characteristics and drug dose. In total, 12,127 potential articles were screened and 146 eligible articles (published from 1979 to 2020) were identified and included for the meta-analysis. We found that there has been no significant reduction in CR or ERR over the study period. The results showed more variability in CR, compared with ERR which was more consistent and remained high. The results showed a positive effect of "PZQ treatment dose" with the current recommended dose of 40 mg/kg body weight achieving 57% to 88% CR depending on schistosome species, age of participants, and number of parasitological samples used for diagnosis, and ERR of 95%. CONCLUSIONS/SIGNIFICANCE Based on a review of over 40 years of research there is no evidence to support concerns about schistosomes developing resistance to PZQ. These results indicate that PZQ remains effective in treating schistosomiasis.
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Affiliation(s)
- Mizuho Fukushige
- Institute of Immunology and Infection Research, Centre for Immunity, Infection & Evolution, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, United Kingdom
- Faculty of Medicine, University of Tsukuba, Ibaraki, Japan
| | - Margo Chase-Topping
- Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom
| | | | - Francisca Mutapi
- Institute of Immunology and Infection Research, Centre for Immunity, Infection & Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
- NIHR Global Health Research Unit Tackling Infections to Benefit Africa (TIBA), University of Edinburgh, Edinburgh, United Kingdom
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Oso OG, Odaibo AB. Human water contact patterns in active schistosomiasis endemic areas. JOURNAL OF WATER AND HEALTH 2020; 18:946-955. [PMID: 33328366 DOI: 10.2166/wh.2020.147] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
One major risk factor common to individuals in schistosomiasis endemic areas is water contact patterns. Effort to determine the dynamics in water contact patterns in different regions needs utmost attention in order to suggest a better control strategy for schistosome infection. Quantitative observations on human water contact activities were recorded in Yewa North Local Government Area of Ogun State for a period of two years. Frequency and duration of observed water contact activities were recorded. Males had the highest water contact during the rainy season with 51.1% compared to females with 48.9%. Females had the highest water contact with 51.0% while males had 49.0% during the dry season. The age group 10-19 years had the highest water contact with 27.1%, this was followed by 20-29 years and 30-39 years age groups with 23.6% and 22.1%, respectively, during the rainy season. Our results showed that water contact activities differ with respect to different communities, sex and age groups. Previous high prevalence of schistosome infection in the study areas could be attributed to high water contact activities. Therefore, provision of adequate pipe-borne water, good sanitation and improved knowledge on schistosome life cycle among the community members will reduce the high rate of human water contacts.
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Affiliation(s)
- O G Oso
- Parasitology Research Unit, Department of Zoology, University of Ibadan, Ibadan, Nigeria E-mail:
| | - A B Odaibo
- Parasitology Research Unit, Department of Zoology, University of Ibadan, Ibadan, Nigeria E-mail:
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Hamley JID, Milton P, Walker M, Basáñez MG. Modelling exposure heterogeneity and density dependence in onchocerciasis using a novel individual-based transmission model, EPIONCHO-IBM: Implications for elimination and data needs. PLoS Negl Trop Dis 2019; 13:e0007557. [PMID: 31805049 PMCID: PMC7006940 DOI: 10.1371/journal.pntd.0007557] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2019] [Revised: 02/07/2020] [Accepted: 06/18/2019] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Density dependence in helminth establishment and heterogeneity in exposure to infection are known to drive resilience to interventions based on mass drug administration (MDA). However, the interaction between these processes is poorly understood. We developed a novel individual-based model for onchocerciasis transmission, EPIONCHO-IBM, which accounts for both processes. We fit the model to pre-intervention epidemiological data and explore parasite dynamics during MDA with ivermectin. METHODOLOGY/PRINCIPAL FINDINGS Density dependence and heterogeneity in exposure to blackfly (vector) bites were estimated by fitting the model to matched pre-intervention microfilarial prevalence, microfilarial intensity and vector biting rate data from savannah areas of Cameroon and Côte d'Ivoire/Burkina Faso using Latin hypercube sampling. Transmission dynamics during 25 years of annual and biannual ivermectin MDA were investigated. Density dependence in parasite establishment within humans was estimated for different levels of (fixed) exposure heterogeneity to understand how parametric uncertainty may influence treatment dynamics. Stronger overdispersion in exposure to blackfly bites results in the estimation of stronger density-dependent parasite establishment within humans, consequently increasing resilience to MDA. For all levels of exposure heterogeneity tested, the model predicts a departure from the functional forms for density dependence assumed in the deterministic version of the model. CONCLUSIONS/SIGNIFICANCE This is the first, stochastic model of onchocerciasis, that accounts for and estimates density-dependent parasite establishment in humans alongside exposure heterogeneity. Capturing the interaction between these processes is fundamental to our understanding of resilience to MDA interventions. Given that uncertainty in these processes results in very different treatment dynamics, collecting data on exposure heterogeneity would be essential for improving model predictions during MDA. We discuss possible ways in which such data may be collected as well as the importance of better understanding the effects of immunological responses on establishing parasites prior to and during ivermectin treatment.
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Affiliation(s)
- Jonathan I. D. Hamley
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s campus), Imperial College London, London, United Kingdom
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s campus), Imperial College London, London, United Kingdom
- * E-mail:
| | - Philip Milton
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s campus), Imperial College London, London, United Kingdom
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s campus), Imperial College London, London, United Kingdom
| | - Martin Walker
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s campus), Imperial College London, London, United Kingdom
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hatfield, Untied Kingdom
| | - Maria-Gloria Basáñez
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s campus), Imperial College London, London, United Kingdom
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s campus), Imperial College London, London, United Kingdom
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Mari L, Ciddio M, Casagrandi R, Perez-Saez J, Bertuzzo E, Rinaldo A, Sokolow SH, De Leo GA, Gatto M. Heterogeneity in schistosomiasis transmission dynamics. J Theor Biol 2017; 432:87-99. [PMID: 28823529 PMCID: PMC5595357 DOI: 10.1016/j.jtbi.2017.08.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 06/30/2017] [Accepted: 08/15/2017] [Indexed: 01/30/2023]
Abstract
Transmission dynamics of schistosomiasis presents multiple heterogeneity sources. A comprehensive framework for heterogeneous disease transmission is proposed. Heterogeneous multigroup communities can be more prone to parasite transmission. Presence of multiple water sources can hinder parasite transmission. Spatial and temporal heterogeneities can have nontrivial implications for endemicity.
Simple models of disease propagation often disregard the effects of transmission heterogeneity on the ecological and epidemiological dynamics associated with host-parasite interactions. However, for some diseases like schistosomiasis, a widespread parasitic infection caused by Schistosoma worms, accounting for heterogeneity is crucial to both characterize long-term dynamics and evaluate opportunities for disease control. Elaborating on the classic Macdonald model for macroparasite transmission, we analyze families of models including explicit descriptions of heterogeneity related to differential transmission risk within a community, water contact patterns, the distribution of the snail host population, human mobility, and the seasonal fluctuations of the environment. Through simple numerical examples, we show that heterogeneous multigroup communities may be more prone to schistosomiasis than homogeneous ones, that the availability of multiple water sources can hinder parasite transmission, and that both spatial and temporal heterogeneities may have nontrivial implications for disease endemicity. Finally, we discuss the implications of heterogeneity for disease control. Although focused on schistosomiasis, results from this study may apply as well to other parasitic infections with complex transmission cycles, such as cysticercosis, dracunculiasis and fasciolosis.
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Affiliation(s)
- Lorenzo Mari
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, 20133 Milano, Italy.
| | - Manuela Ciddio
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, 20133 Milano, Italy
| | - Renato Casagrandi
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, 20133 Milano, Italy
| | - Javier Perez-Saez
- Laboratory of Ecohydrology, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
| | - Enrico Bertuzzo
- Dipartimento di Scienze Ambientali, Informatica e Statistica, Università Ca' Foscari Venezia, 30170 Venezia Mestre, Italy
| | - Andrea Rinaldo
- Laboratory of Ecohydrology, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland; Dipartimento ICEA, Università di Padova, 35131 Padova, Italy
| | - Susanne H Sokolow
- Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA; Marine Science Institute, University of California, Santa Barbara, CA 93106, USA
| | - Giulio A De Leo
- Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA
| | - Marino Gatto
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, 20133 Milano, Italy
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Useh MF, Ejezie GC. Modification of behaviour and attitude in the control of schistosomiasis. 1. Observations on water-contact patterns and perception of infection. ANNALS OF TROPICAL MEDICINE AND PARASITOLOGY 2016. [DOI: 10.1080/00034983.1999.11813476] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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Gurarie D, King CH, Yoon N, Li E. Refined stratified-worm-burden models that incorporate specific biological features of human and snail hosts provide better estimates of Schistosoma diagnosis, transmission, and control. Parasit Vectors 2016; 9:428. [PMID: 27492409 PMCID: PMC4973538 DOI: 10.1186/s13071-016-1681-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 07/05/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Schistosoma parasites sustain a complex transmission process that cycles between a definitive human host, two free-swimming larval stages, and an intermediate snail host. Multiple factors modify their transmission and affect their control, including heterogeneity in host populations and environment, the aggregated distribution of human worm burdens, and features of parasite reproduction and host snail biology. Because these factors serve to enhance local transmission, their inclusion is important in attempting accurate quantitative prediction of the outcomes of schistosomiasis control programs. However, their inclusion raises many mathematical and computational challenges. To address these, we have recently developed a tractable stratified worm burden (SWB) model that occupies an intermediate place between simpler deterministic mean worm burden models and the very computationally-intensive, autonomous agent models. METHODS To refine the accuracy of model predictions, we modified an earlier version of the SWB by incorporating factors representing essential in-host biology (parasite mating, aggregation, density-dependent fecundity, and random egg-release) into demographically structured host communities. We also revised the snail component of the transmission model to reflect a saturable form of human-to-snail transmission. The new model allowed us to realistically simulate overdispersed egg-test results observed in individual-level field data. We further developed a Bayesian-type calibration methodology that accounted for model and data uncertainties. RESULTS The new model methodology was applied to multi-year, individual-level field data on S. haematobium infections in coastal Kenya. We successfully derived age-specific estimates of worm burden distributions and worm fecundity and crowding functions for children and adults. Estimates from the new SWB model were compared with those from the older, simpler SWB with some substantial differences noted. We validated our new SWB estimates in prediction of drug treatment-based control outcomes for a typical Kenyan community. CONCLUSIONS The new version of the SWB model provides a better tool to predict the outcomes of ongoing schistosomiasis control programs. It reflects parasite features that augment and perpetuate transmission, while it also readily incorporates differences in diagnostic testing and human sub-population differences in treatment coverage. Once extended to other Schistosoma species and transmission environments, it will provide a useful and efficient tool for planning control and elimination strategies.
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Affiliation(s)
- 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, 10900 Euclid Avenue, Cleveland, Ohio, USA
| | - Charles H King
- Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA. .,Schistosomiasis Consortium for Operational Research and Evaluation, University of Georgia, Athens, Georgia, USA.
| | - Nara Yoon
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, Cleveland, USA
| | - Emily Li
- Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio, USA
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Monde C, Syampungani S, van den Brink PJ. Natural and human induced factors influencing the abundance of Schistosoma host snails in Zambia. ENVIRONMENTAL MONITORING AND ASSESSMENT 2016; 188:370. [PMID: 27230422 PMCID: PMC4882361 DOI: 10.1007/s10661-016-5351-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 05/05/2016] [Indexed: 06/05/2023]
Abstract
Schistosomiasis remains a global public health problem affecting about 240 million people. In Zambia, 2 million are infected while 3 million live with the risk of getting infected. Research and interventions relating to schistosomiasis are mainly linked to disease epidemiology. Malacological and ecological aspects of the disease are superficially understood. Developing effective control measures requires an understanding of interacting environmental and socioeconomic factors of host snails vis-a-vis schistosomiasis. Therefore, the present work involved collecting social and environmental data in a large field study in two zones in Zambia that are different in terms of temperature and rainfall amounts. Social data collected through questionnaires included demographic, educational and knowledge of schistosomiasis disease dynamics. Environmental data included physicochemical factors, aquatic plants and snails. Gender (P < 0.001) significantly influences livelihood strategies, while age (P = 0.069) and level of education (P = 0.086) have a moderate influence in zone I. In zone III, none of these factors (age, P = 0.378; gender, P = 0.311; education, P = 0.553) play a significant role. Environmental parameters explained 43 and 41 % variation in species composition for zones I and III, respectively. Most respondents' (52 %, 87 %) perception is that there are more cases of bilharzia in hot season than in other seasons (rainy season 23 %, 7 %; cold season 8 %, 0 % and year round 17 %, 6 %) for zone I and zone III, respectively.
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Affiliation(s)
- Concillia Monde
- Department of Aquatic Ecology and Water Quality Management, Wageningen University and Research Centre, P.O. Box 47, 6700 AA, Wageningen, The Netherlands.
- Department of Zoology and Aquatic Sciences, Copperbelt University, P.O. Box 21692, Jambo Drive, Riverside, Kitwe, Zambia.
| | - Stephen Syampungani
- Department of Plant and Environmental Sciences, Copperbelt University, P.O Box 21692, Jambo Drive, Riverside, Kitwe, Zambia
| | - Paul J van den Brink
- Department of Aquatic Ecology and Water Quality Management, Wageningen University and Research Centre, P.O. Box 47, 6700 AA, Wageningen, The Netherlands
- Alterra, Wageningen University and Research Centre, P.O. Box 47, 6700 AA, Wageningen, The Netherlands
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Grimes JET, Croll D, Harrison WE, Utzinger J, Freeman MC, Templeton MR. The roles of water, sanitation and hygiene in reducing schistosomiasis: a review. Parasit Vectors 2015; 8:156. [PMID: 25884172 PMCID: PMC4377019 DOI: 10.1186/s13071-015-0766-9] [Citation(s) in RCA: 135] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 02/18/2015] [Indexed: 11/10/2022] Open
Abstract
Schistosomiasis is a disease caused by infection with blood flukes of the genus Schistosoma. Transmission of, and exposure to, the parasite result from faecal or urinary contamination of freshwater containing intermediate host snails, and dermal contact with the same water. The World Health Assembly resolution 65.21 from May 2012 urges member states to eliminate schistosomiasis through preventive chemotherapy (i.e. periodic large-scale administration of the antischistosomal drug praziquantel to school-aged children and other high-risk groups), provision of water, sanitation and hygiene (WASH) and snail control. However, control measures focus almost exclusively on preventive chemotherapy, while only few studies made an attempt to determine the impact of upgraded access to safe water, adequate sanitation and good hygiene on schistosome transmission. We recently completed a systematic review and meta-analysis pertaining to WASH and schistosomiasis and found that people with safe water and adequate sanitation have significantly lower odds of a Schistosoma infection. Importantly though, the transmission of schistosomiasis is deeply entrenched in social-ecological systems, and hence is governed by setting-specific cultural and environmental factors that determine human behaviour and snail populations. Here, we provide a comprehensive review of the literature, which explores the transmission routes of schistosomes, particularly focussing on how these might be disrupted with WASH-related technologies and human behaviour. Additionally, future research directions in this area are highlighted.
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Affiliation(s)
- Jack E T Grimes
- Department of Civil and Environmental Engineering, Imperial College London, London, SW7 2AZ, UK.
| | - David Croll
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, , CH-4002, Basel, Switzerland. .,University of Basel, P.O. Box, , CH-4003, Basel, Switzerland.
| | - Wendy E Harrison
- Schistosomiasis Control Initiative, Imperial College London, London, SW7 2AZ, UK.
| | - Jürg Utzinger
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, , CH-4002, Basel, Switzerland. .,University of Basel, P.O. Box, , CH-4003, Basel, Switzerland.
| | - Matthew C Freeman
- Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA, 30322, USA.
| | - Michael R Templeton
- Department of Civil and Environmental Engineering, Imperial College London, London, SW7 2AZ, UK.
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Appleby LJ, Nausch N, Heard F, Erskine L, Bourke CD, Midzi N, Mduluza T, Allen JE, Mutapi F. Down Regulation of the TCR Complex CD3ζ-Chain on CD3+ T Cells: A Potential Mechanism for Helminth-Mediated Immune Modulation. Front Immunol 2015; 6:51. [PMID: 25741337 PMCID: PMC4332365 DOI: 10.3389/fimmu.2015.00051] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Accepted: 01/27/2015] [Indexed: 01/30/2023] Open
Abstract
The CD3ζ forms part of the T cell receptor (TCR) where it plays an important role in coupling antigen recognition to several intracellular signal-transduction pathways leading to T cell effector functions. Down regulation of CD3ζ leads to impairment of immune responses including reduced cell proliferation and cytokine production. In experimental models, helminth parasites have been shown to modulate immune responses directed against them and unrelated antigens, so called bystander antigens, but there is a lack of studies validating these observations in humans. This study investigated the relationship between expression levels of the TCR CD3ζ chain with lymphocyte cell proliferation during human infection with the helminth parasite, Schistosoma haematobium, which causes uro-genital schistosomiasis. Using flow cytometry, peripheral blood mononuclear cells (PBMCs) from individuals naturally exposed to S. haematobium in rural Zimbabwe were phenotyped, and expression levels of CD3ζ on T cells were related to intensity of infection. In this population, parasite infection intensity was inversely related to CD3ζ expression levels (p < 0.05), consistent with downregulation of CD3ζ expression during helminth infection. Furthermore, PBMC proliferation was positively related to expression levels of CD3ζ (p < 0.05) after allowing for confounding variables (host age, sex, and infection level). CD3ζ expression levels had a differing relationship between immune correlates of susceptibility and immunity, measured by antibody responses, indicating a complex relationship between immune activation status and immunity. The relationships between the CD3ζ chain of the TCR and schistosome infection, PBMC proliferation and schistosome-specific antibody responses have not previously been reported, and these results may indicate a mechanism for the impaired T cell proliferative responses observed during human schistosome infection.
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Affiliation(s)
- Laura J Appleby
- Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh , Edinburgh , UK
| | - Norman Nausch
- Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh , Edinburgh , UK
| | - Francesca Heard
- Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh , Edinburgh , UK
| | - Louise Erskine
- Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh , Edinburgh , UK
| | - Claire D Bourke
- Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh , Edinburgh , UK
| | - Nicholas Midzi
- National Institutes of Health Research , Harare , Zimbabwe
| | - Takafira Mduluza
- Department of Biochemistry, University of Zimbabwe , Harare , Zimbabwe
| | - Judith E Allen
- Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh , Edinburgh , UK
| | - Francisca Mutapi
- Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh , Edinburgh , UK
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CD16 expression on monocytes in healthy individuals but not schistosome-infected patients is positively associated with levels of parasite-specific IgG and IgG1. PLoS Negl Trop Dis 2014; 8:e3049. [PMID: 25101623 PMCID: PMC4125298 DOI: 10.1371/journal.pntd.0003049] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 06/16/2014] [Indexed: 02/06/2023] Open
Abstract
Human IgG1 antibody responses are associated with protection against Schistosoma haematobium infection and are now a target for schistosome vaccine development. This study aimed to investigate the relationship between total IgG and the IgG subclasses and the monocyte IgG receptor, known as FcγRIIIa or CD16, in schistosome exposed people. Systemic levels of schistosome-specific anti-adult worm total IgG and IgG subclass titres were measured by ELISA in 100 individuals from an S. haematobium endemic area in Zimbabwe and, using parametric statistical methods and regression analysis, related to the levels of CD16 expression on individuals' circulating monocytes, determined via flow cytometry. Monocyte CD16 expression rose with parasite-specific total IgG and IgG1 in healthy participants, but not in schistosome infected patients. Similar to parasite-specific IgG and IgG1, CD16 expression in healthy individuals is associated with protection against schistosome infection. This relationship indicates a mechanistic link between the innate and adaptive immune responses to helminth infection in protection against infection. Further understanding the elements of a protective immune response in schistosomiasis may aid in efforts to develop a protective vaccine against this disease. Schistosomiasis is a parasitic disease caused by the parasite Schistosoma spp. Over 240 million people are infected worldwide, mainly in Sub-Saharan Africa, but an efficacious, protective vaccine has yet to be found. Protection against schistosome infection in individuals living in endemic areas is mediated by antibodies. In particular, IgG1 antibody has been shown to be protective against infection in individuals living in endemic areas, and eliciting IgG1 production has become a cornerstone of vaccine development efforts. However, little is known about the mechanisms by which IgG1 induces protection. The cell surface molecule CD16 is an IgG antibody receptor expressed on monocytes and binds preferentially to IgG antibody subclasses. The work presented here thus investigates the relationship between IgG levels and the monocyte CD16 receptor in a population endemically exposed to infection with schistosomes. We present results linking CD16 expression with IgG1 levels, whereby uninfected individuals have a positive relationship between IgG1 and CD16 expression levels, while schistosome infected individuals did not show any statistically significant relationship between the two. Thus we provide evidence to suggest a mechanistic link between the innate and adaptive immune response in parasitic infection, associating monocyte CD16 expression with a protective immune response.
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Kjetland EF, Hegertun IEA, Baay MFD, Onsrud M, Ndhlovu PD, Taylor M. Genital schistosomiasis and its unacknowledged role on HIV transmission in the STD intervention studies. Int J STD AIDS 2014; 25:705-15. [DOI: 10.1177/0956462414523743] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Treatment of sexually transmitted infections (STIs) has been hypothesised to decrease HIV transmission. Although observational studies show an association between STIs and HIV, only one prospective randomised controlled trial (RCT) has confirmed this. Female genital schistosomiasis can cause genital lesions, accompanied by bloody discharge, ulcers or malodorous discharge. Genital schistosomiasis is common, starts before puberty and symptoms can be mistaken for STIs. Three observational studies have found an association between schistosomiasis and HIV. Genital lesions that develop in childhood are chronic. This paper sought to explore the possible effects of schistosomiasis on the RCTs of STI treatment for HIV prevention. In the study sites, schistosomiasis was a likely cause of genital lesions. The studies recruited women that may have had genital schistosomal lesions established in childhood. Schistosomiasis endemic areas with different prevalence levels may have influenced HIV incidence in intervention and control sites differently, and some control group interventions may have influenced the impact of schistosomiasis on the study results. Schistosomiasis is a neglected cause of genital tract disease. It may have been an independent cause of HIV incidence in the RCTs of STI treatment for HIV prevention and may have obscured the findings of these trials.
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Affiliation(s)
- Eyrun F Kjetland
- Norwegian Centre for Imported and Tropical Diseases, Department of Infectious Diseases Ullevaal, Oslo University Hospital, Oslo, Norway
- Discipline of Public Health Medicine, Nelson R Mandela School of Medicine, School of Public Health, College of Health Sciences, University of KwaZulu-Natal, Durban, South Africa
| | - Ingrid EA Hegertun
- Norwegian Centre for Imported and Tropical Diseases, Department of Infectious Diseases Ullevaal, Oslo University Hospital, Oslo, Norway
| | - Marc FD Baay
- Norwegian Centre for Imported and Tropical Diseases, Department of Infectious Diseases Ullevaal, Oslo University Hospital, Oslo, Norway
- Laboratory of Cancer Research and Clinical Oncology, University of Antwerp, Wilrijk, Belgium
| | - Mathias Onsrud
- Department of Gynaecology and Obstetrics, Oslo University Hospital, Oslo, Norway
| | | | - Myra Taylor
- Discipline of Public Health Medicine, Nelson R Mandela School of Medicine, School of Public Health, College of Health Sciences, University of KwaZulu-Natal, Durban, South Africa
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Carlton EJ, Hubbard A, Wang S, Spear RC. Repeated Schistosoma japonicum infection following treatment in two cohorts: evidence for host susceptibility to helminthiasis? PLoS Negl Trop Dis 2013; 7:e2098. [PMID: 23505589 PMCID: PMC3591324 DOI: 10.1371/journal.pntd.0002098] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 01/24/2013] [Indexed: 02/04/2023] Open
Abstract
Background In light of multinational efforts to reduce helminthiasis, we evaluated whether there exist high-risk subpopulations for helminth infection. Such individuals are not only at risk of morbidity, but may be important parasite reservoirs and appropriate targets for disease control interventions. Methods/Principal Findings We followed two longitudinal cohorts in Sichuan, China to determine whether there exist persistent human reservoirs for the water-borne helminth, Schistosoma japonicum, in areas where treatment is ongoing. Participants were tested for S. japonicum infection at enrollment and two follow-up points. All infections were promptly treated with praziquantel. We estimated the ratio of the observed to expected proportion of the population with two consecutive infections at follow-up. The expected proportion was estimated using a prevalence-based model and, as highly exposed individuals may be most likely to be repeatedly infected, a second model that accounted for exposure using a data adaptive, machine learning algorithm. Using the prevalence-based model, there were 1.5 and 5.8 times more individuals with two consecutive infections than expected in cohorts 1 and 2, respectively (p<0.001 in both cohorts). When we accounted for exposure, the ratio was 1.3 (p = 0.013) and 2.1 (p<0.001) in cohorts 1 and 2, respectively. Conclusions/Significance We found clustering of infections within a limited number of hosts that was not fully explained by host exposure. This suggests some hosts may be particularly susceptible to S. japonicum infection, or that uncured infections persist despite treatment. We propose an explanatory model that suggests that as cercarial exposure declines, so too does the size of the vulnerable subpopulation. In low-prevalence settings, interventions targeting individuals with a history of S. japonicum infection may efficiently advance disease control efforts. Approximately 1 billion people are infected with one or more helminthes – a class of parasites that can impair physical, mental and economic development. We are interested in whether there exist groups who are repeatedly infected with helminthes over time in areas where treatment is ongoing. Such individuals may be at risk of morbidity and may also serve as parasite reservoirs, making them appropriate targets for disease control programs. We followed two cohorts in rural Sichuan, China in order to evaluate whether the same individuals were repeatedly infected with the water-borne helminth, Schistosoma japonicum. Each participant was tested for infection at enrollment and two follow-up points – all infections were promptly treated. We conducted detailed interviews to assess exposures to S. japonicum. We found infections repeatedly occurred in a subgroup of individuals and this clustering of infections was only partly explained by differences in exposure. This suggests some individuals may be particularly susceptible to S. japonicum infection. Further exploration of the interplay of exposure and susceptibility suggest that as exposure declines, so too does the fraction of the population vulnerable to infection. Helminth control programs that target people with a history of infection may efficiently reduce helminth infections and morbidity.
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Affiliation(s)
- Elizabeth J Carlton
- Environmental Health Sciences, School of Public Health, University of California, Berkeley, California, United States of America.
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16
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Enhancing schistosomiasis control strategy for zimbabwe: building on past experiences. J Parasitol Res 2012; 2012:353768. [PMID: 22655171 PMCID: PMC3357947 DOI: 10.1155/2012/353768] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Accepted: 02/20/2012] [Indexed: 11/17/2022] Open
Abstract
Schistosoma haematobium and Schistosoma mansoni are prevalent in Zimbabwe to levels that make schistosomiasis a public health problem. Following three national surveys to map the disease prevalence, a national policy on control of schistosomiasis and soil transmitted helminths is being developed. This paper reviews the experiences that Zimbabwe has in the area of schistosomiasis control with a view to influence policy. A case study approach to highlight key experiences and outcomes was adopted. The benefits derived from intersectoral collaboration that led to the development of a model irrigation scheme that incorporates schistosomiasis control measures are highlighted. Similarly, the benefits of using plant molluscicides and fish and duck biological agents (Sargochromis codringtonii and Cairina moschata) are highlighted. Emphasis was also placed on the importance of utilizing locally developed water and sanitation technologies and the critical human resource base in the area of schistosomiasis developed over years. After synthesis of the case studies presented, it was concluded that while there is a need to follow the WHO recommended guidelines for schistosomiasis control it is important to develop a control strategy that is informed by work already done in the country. The importance of having a policy and local guidelines for schistosomiasis control is emphasized.
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17
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Mitchell KM, Mutapi F, Savill NJ, Woolhouse MEJ. Explaining observed infection and antibody age-profiles in populations with urogenital schistosomiasis. PLoS Comput Biol 2011; 7:e1002237. [PMID: 22028640 PMCID: PMC3197645 DOI: 10.1371/journal.pcbi.1002237] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Accepted: 09/04/2011] [Indexed: 01/05/2023] Open
Abstract
Urogenital schistosomiasis is a tropical disease infecting more than 100 million people in sub-Saharan Africa. Individuals in endemic areas endure repeated infections with long-lived schistosome worms, and also encounter larval and egg stages of the life cycle. Protective immunity against infection develops slowly with age. Distinctive age-related patterns of infection and specific antibody responses are seen in endemic areas, including an infection 'peak shift' and a switch in the antibody types produced. Deterministic models describing changing levels of infection and antibody with age in homogeneously exposed populations were developed to identify the key mechanisms underlying the antibody switch, and to test two theories for the slow development of protective immunity: that (i) exposure to dying (long-lived) worms, or (ii) experience of a threshold level of antigen, is necessary to stimulate protective antibody. Different model structures were explored, including alternative stages of the life cycle as the main antigenic source and the principal target of protective antibody, different worm survival distributions, antigen thresholds and immune cross-regulation. Models were identified which could reproduce patterns of infection and antibody consistent with field data. Models with dying worms as the main source of protective antigen could reproduce all of these patterns, but so could some models with other continually-encountered life stages acting as the principal antigen source. An antigen threshold enhanced the ability of the model to replicate these patterns, but was not essential for it to do so. Models including either non-exponential worm survival or cross-regulation were more likely to be able to reproduce field patterns, but neither of these was absolutely required. The combination of life cycle stage stimulating, and targeted by, antibody was found to be critical in determining whether models could successfully reproduce patterns in the data, and a number of combinations were excluded as being inconsistent with field data.
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Affiliation(s)
- Kate M Mitchell
- Centre for Immunology, Infection and Evolution, Institute of Immunology & Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
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Sow S, de Vlas SJ, Stelma F, Vereecken K, Gryseels B, Polman K. The contribution of water contact behavior to the high Schistosoma mansoni Infection rates observed in the Senegal River Basin. BMC Infect Dis 2011; 11:198. [PMID: 21767372 PMCID: PMC3160997 DOI: 10.1186/1471-2334-11-198] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Accepted: 07/18/2011] [Indexed: 11/29/2022] Open
Abstract
Background Schistosomiasis is one of the major parasitic diseases in the world in terms of people infected and those at risk. Infection occurs through contact with water contaminated with larval forms of the parasite, which are released by freshwater snails and then penetrate the skin of people. Schistosomiasis infection and human water contact are thus essentially linked, and more knowledge about their relationship will help us to develop appropriate control measures. So far, only few studies have related water contact patterns to infection levels. Methods We have conducted detailed direct water contact observations in a village in Northern Senegal during the first years of a massive Schistosoma mansoni outbreak to determine the role of human water contact in the extent of the epidemic. We quantified water contact activities in terms of frequency and duration, and described how these vary with age and sex. Moreover, we assessed the relationship between water contact- and infection intensity patterns to further elucidate the contribution of exposure to the transmission of schistosomiasis. Results This resulted in over 120,000 recorded water contacts for 1651 subjects over 175 observation days. Bathing was the main activity, followed by household activities. Frequency and duration of water contact depended on age and sex rather than season. Water contacts peaked in adolescents, women spent almost twice as much time in the water as men, and water contacts were more intense in the afternoon than in the morning, with sex-specific intensity peaks. The average number of water contacts per person per day in this population was 0.42; the average time spent in the water per person per day was 4.3 minutes. Conclusions The observed patterns of water contact behavior are not unusual and have been described before in various other settings in sub-Saharan Africa. Moreover, water contact levels were not exceptionally high and thus cannot explain the extremely high S. mansoni infection intensities as observed in Northern Senegal. Comparison with fecal egg counts in the respective age and sex groups further revealed that water contact levels did not unambiguously correspond with infection levels, indicating that factors other than exposure also play a role in determining intensity of infection.
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Affiliation(s)
- Seydou Sow
- Prince Leopold Institute of Tropical Medicine, Antwerp, Belgium
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Abstract
A characteristic relationship between infection and host age, with levels of infection reaching a peak in particular age classes, has been reported for many parasites. However, several field studies have shown that this relationship is not invariant: if age-infection data are compared across host populations, the peak level of infection is higher and occurs at a younger age when the transmission rate is high, and is lower and occurs at an older age when it is low. This pattern is called the ;peak shift'. Here, Mark Woolhouse reviews the evidence for and the implications of the peak shift. The peak shift is consistent with the predictions of mathematical models that assume gradually acquired protective immunity, and this interpretation is supported by experimental studies using animals. This agreement between theory, experimental evidence and field studies strongly suggests that acquired immunity has a major impact on epidemiological patterns not only for parasites such as malaria, where the importance of acquired immunity is not in doubt, but also for many parasitic helminths, where the role of acquired immunity is less widely accepted.
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Affiliation(s)
- M E Woolhouse
- Centre for Tropical Veterinary Medicine, University of Edinburgh, Easter Bush, Roslin, Midlothian, UK EH25 9RG
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Midzi N, Mtapuri-Zinyowera S, Sangweme D, Paul NH, Makware G, Mapingure MP, Brouwer KC, Mudzori J, Hlerema G, Chadukura V, Mutapi F, Kumar N, Mduluza T. Efficacy of integrated school based de-worming and prompt malaria treatment on helminths -Plasmodium falciparum co-infections: A 33 months follow up study. BMC INTERNATIONAL HEALTH AND HUMAN RIGHTS 2011; 11:9. [PMID: 21696629 PMCID: PMC3141662 DOI: 10.1186/1472-698x-11-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Accepted: 06/22/2011] [Indexed: 11/10/2022]
Abstract
Background The geographical congruency in distribution of helminths and Plasmodium falciparum makes polyparasitism a common phenomenon in Sub Saharan Africa. The devastating effects of helminths-Plasmodium co-infections on primary school health have raised global interest for integrated control. However little is known on the feasibility, timing and efficacy of integrated helminths-Plasmodium control strategies. A study was conducted in Zimbabwe to evaluate the efficacy of repeated combined school based antihelminthic and prompt malaria treatment. Methods A cohort of primary schoolchildren (5-17 years) received combined Praziquantel, albendazole treatment at baseline, and again during 6, 12 and 33 months follow up surveys and sustained prompt malaria treatment. Sustained prompt malaria treatment was carried out throughout the study period. Children's infection status with helminths, Plasmodium and helminths-Plasmodium co-infections was determined by parasitological examinations at baseline and at each treatment point. The prevalence of S. haematobium, S. mansoni, STH, malaria, helminths-Plasmodium co-infections and helminths infection intensities before and after treatment were analysed. Results Longitudinal data showed that two rounds of combined Praziquantel and albendazole treatment for schistosomiasis and STHs at 6 monthly intervals and sustained prompt malaria treatment significantly reduced the overall prevalence of S. haematobium, S. mansoni, hookworms and P. falciparum infection in primary schoolchildren by 73.5%, 70.8%, 67.3% and 58.8% respectively (p < 0.001, p < 0.001, p < 0.001, p < 0.001 respectively). More importantly, the prevalence of STH + schistosomes, P. f + schistosomes, and P. f + STHs + schistosomes co-infections were reduced by 68.0%, 84.2%, and 90.7%, respectively. The absence of anti-helminthic treatment between the 12 mth and 33 mth follow-up surveys resulted in the sharp increase in STHs + schistosomes co-infection from 3.3% at 12 months follow up survey to 10.7%, slightly more than the baseline level (10.3%) while other co-infection combinations remained significantly low. The overall prevalence of heavy S. haematobium, S. mansoni and hookworms infection intensities were significantly reduced from: 17.9-22.4% to 2.6-5.1%, 1.6-3.3% to 0.0% and 0.0-0.7% to 0.0% respectively. Conclusion Biannual Integrated school based antihelminthic and sustained prompt malaria treatment has a potential to reduce the burden of helminths-plasmodium co-infections in primary school children. In areas of stable malaria transmission, active case finding is recommended to track and treat asymptomatic malaria cases as these may sustain transmission in the community.
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Affiliation(s)
- Nicholas Midzi
- University of Zimbabwe, Department of Biochemistry, P,O Box MP167, Mount Pleasant, Harare, Zimbabwe.
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21
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Midzi N, Mtapuri-Zinyowera S, Mapingure MP, Paul NH, Sangweme D, Hlerema G, Mutsaka MJ, Tongogara F, Makware G, Chadukura V, Brouwer KC, Mutapi F, Kumar N, Mduluza T. Knowledge attitudes and practices of grade three primary schoolchildren in relation to schistosomiasis, soil transmitted helminthiasis and malaria in Zimbabwe. BMC Infect Dis 2011; 11:169. [PMID: 21668948 PMCID: PMC3141409 DOI: 10.1186/1471-2334-11-169] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 06/13/2011] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Helminth infection rates in grade three children are used as proxy indicators of community infection status and to guide treatment strategies in endemic areas. However knowledge, attitudes and practices (KAP) of this target age group (8-10 years) in relation to schistosomiasis, soil transmitted helminthiasis (STHs) and malaria is not known at a time when integrated plasmodium - helminth control strategies are being advocated. This study sought to assess KAP of grade 3 children in relation to schistosomiasis, STHs and malaria in order to establish an effective school based health education for disease transmission control. METHODS Grade 3 children (n = 172) attending four randomly selected primary schools (one in rural and 3 in the commercial farming areas) in Zimbabwe were interviewed using a pre-tested interviewer administered questionnaire. The urine filtration technique was used to determine S. haematobium infection status. Infection with S. mansoni and STHs was determined using a combination of results from the Kato Katz and formol ether concentration techniques. P. falciparum was diagnosed by examination of Giemsa stained thick blood smears. RESULTS It was observed that 32.0%, 19.2% and 4.1% of the respondents had correct knowledge about the causes of schistosomiasis, malaria and STHs, respectively, whilst 22.1%, 19.2% and 5.8% knew correct measures to control schistosomiasis, malaria and STHs. Sixty-two percent and 44.8% did not use soap to wash hands after toilet and before eating food respectively, whilst 33.1% never wore shoes. There were no functional water points and soap for hand washing after toilet at all schools. There was a high prevalence distribution of all parasites investigated in this study at Msapa primary school - S. haematobium (77.8%), S. mansoni (33.3%) hookworms (29.6%) and P. falciparum (48.1%). Reports that participant had suffered from schistosomiasis and malaria before were significant predictors of these diseases (p = 0.001 and p = 0.042, respectively). Report that participant had blood in urine on the day of examination was a significant predictor of schistosomiasis (p = 0.045). CONCLUSION There is a critical need for targeting health messages through schools in order to reach the most susceptible schoolchildren. This will empower the schoolchildren with the basic knowledge and skills ultimately protecting them from acquiring schistosomiasis, STHs and malaria.
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Affiliation(s)
- Nicholas Midzi
- National Institute of Health Research, Box CY 573, Causeway Harare, Zimbabwe
| | - Sekesai Mtapuri-Zinyowera
- College of Health Sciences, Department of Medical Microbiology, P.0 Box A178, Avondale, Harare, Zimbabwe
| | - Munyaradzi P Mapingure
- University of Zimbabwe, Department of Biochemistry, P.O Box MP167, Mount Pleasant, Harare, Zimbabwe
| | - Noah H Paul
- University of Zimbabwe, Department of Biochemistry, P.O Box MP167, Mount Pleasant, Harare, Zimbabwe
| | - Davison Sangweme
- Johns Hopkins Bloomberg School of Public Health, Department of Molecular Microbiology and Immunology, Baltimore, Maryland, USA
| | - Gibson Hlerema
- National Institute of Health Research, Box CY 573, Causeway Harare, Zimbabwe
| | - Masceline J Mutsaka
- National Institute of Health Research, Box CY 573, Causeway Harare, Zimbabwe
| | - Farisai Tongogara
- National Institute of Health Research, Box CY 573, Causeway Harare, Zimbabwe
| | - Godfrey Makware
- Zimbabwe National Statistics Agency PO Box CY 342, Causeway, Harare, Zimbabwe
| | - Vivian Chadukura
- National Institute of Health Research, Box CY 573, Causeway Harare, Zimbabwe
| | - Kimberly C Brouwer
- University of California, San Diego, Division of Global Public Health, Department of Medicine, San Diego, California USA
| | - Francisca Mutapi
- University of Edinburgh, Institute for Immunology and Infection Research, Edinburgh, UK
| | - Nirbhay Kumar
- Johns Hopkins Bloomberg School of Public Health, Department of Molecular Microbiology and Immunology, Baltimore, Maryland, USA
| | - Takafira Mduluza
- University of Zimbabwe, Department of Biochemistry, P.O Box MP167, Mount Pleasant, Harare, Zimbabwe
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Clerinx J, Van Gompel A. Schistosomiasis in travellers and migrants. Travel Med Infect Dis 2011; 9:6-24. [DOI: 10.1016/j.tmaid.2010.11.002] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2010] [Revised: 11/09/2010] [Accepted: 11/18/2010] [Indexed: 02/07/2023]
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Pinot de Moira A, Fulford AJC, Kabatereine NB, Ouma JH, Booth M, Dunne DW. Analysis of complex patterns of human exposure and immunity to Schistosomiasis mansoni: the influence of age, sex, ethnicity and IgE. PLoS Negl Trop Dis 2010; 4. [PMID: 20856909 PMCID: PMC2939029 DOI: 10.1371/journal.pntd.0000820] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Accepted: 08/12/2010] [Indexed: 11/25/2022] Open
Abstract
Background Numerous factors may influence Schistosoma infection intensity and prevalence within endemic communities, including exposure-related factors such as local environment and behaviour, and factors relating to susceptibility to infection such as immunology and genetics. While animal studies performed in the laboratory can be tightly controlled, human populations are highly heterogeneous, varying according to demographic characteristics, genetic background and exposure to infection. The heterogeneous nature of human water contact behaviour in particular makes it difficult to distinguish between a lack of cercarial exposure and reduced susceptibility to infection as the cause for low levels of infection in the field. Methods and Principal Findings In this study we investigate risk factors for Schistosoma mansoni infection in a rural Ugandan fishing community receiving treatment as part of a multi-disciplinary longitudinal reinfection study. More specifically, we examine the influence that age, sex and ethnic background have on susceptibility to reinfection after anti-helminth drug treatment, but use individual estimates of cercarial exposure and multivariable methods in an attempt to remove noise created by environmental and behavioural heterogeneities. We then investigate whether schistosome-specific IgE immune responses could account for any remaining variations in susceptibility to reinfection. Our findings suggest that observed ethnic- and sex-related variations in S. mansoni reinfection were due to variations in cercarial exposure, as opposed to biological differences in susceptibility to infection. Age-related differences in reinfection were not explained by exposure, however, and appeared linked to the balance of IgE and IgG4 to the tegumental antigen SmTAL1 (formerly Sm22.6), which itself was significantly related to resistance to reinfection. Conclusions This study highlights the benefit of taking a multidisciplinary approach in complex field settings; it allows the ecology of a population to be understood and thus more robust conclusions to be made. Human schistosomiasis is a chronic parasitic disease affecting around 200 million people worldwide. Infection occurs when cercariae penetrate the skin during water contact. Although there is effective treatment for schistosomiasis, individuals remain susceptible to reinfection after treatment; some individuals, however, appear more susceptible to reinfection than others. The highly heterogeneous nature of human water contact behaviour makes it difficult to identify whether low levels of reinfection are caused by immunity or a simple lack of cercarial exposure; this complicates the characterisation of risk factors for infection and immune correlates of protection. Here, we take a multidisciplinary approach using individual estimates of cercarial exposure and multivariable analysis to allow for environmental and behavioural heterogeneities. We examine the influence of demographic factors and antibody responses on susceptibility to reinfection. While observed ethnic- and sex-related variations in Schistosoma mansoni reinfection could be explained by differences in exposure, age-related differences appeared linked to the balance of specific IgE and IgG4 antibodies, themselves related to resistance to reinfection. Our study highlights the benefits of a multidisciplinary approach in complex field settings: it improves our understanding of a population's ecology and therefore the biology of disease.
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Pereira WR, Kloos H, Crawford SB, Velásquez-Melendez JG, Matoso LF, Fujiwara RT, Cançado GGL, Loverde PT, Correa-Oliveira R, Gazzinelli A. Schistosoma mansoni infection in a rural area of the Jequitinhonha Valley, Minas Gerais, Brazil: analysis of exposure risk. Acta Trop 2010; 113:34-41. [PMID: 19765542 DOI: 10.1016/j.actatropica.2009.09.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2008] [Revised: 08/05/2009] [Accepted: 09/09/2009] [Indexed: 11/18/2022]
Abstract
This study examines the relative contribution of age-specific total IgE levels, eosinophils and water contact behavior to the prevalence and intensity (geometric mean egg counts) of Schistosoma mansoni infection in the poor rural population of Virgem das Graças in northern Minas Gerais State. In bivariate analysis, age was strongly correlated with both prevalence and intensity of infection, while eosinophil levels with prevalence only (p<0.0001); IgE levels and 5 demographic and socioeconomic variables were moderately correlated with prevalence (p<0.05), as were number of persons per room and TBM (total body minutes) with egg counts. In multivariate analysis, after controlling for demographic and socioeconomic factors, only total IgE levels were significantly correlated with both prevalence (p=0.248, 95% CI=1.01-1.11) and intensity (p=0.0217, 95% CI=0.01-0.14) of infection and eosinophil levels with prevalence (p=0.0005, 95% CI=1.07-1.24). Although any causal relationship cannot be confirmed by a cross-sectional study, we demonstrated an associated decrease in prevalence and intensity of S. mansoni infection with increased IgE levels.
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Affiliation(s)
- Wesley Rodrigues Pereira
- Laboratory of Cellular and Molecular Immunology, Centro de Pesquisas René Rachou/FIOCRUZ, Brazil
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Lillerud LE, Stuestoel VM, Hoel RE, Rukeba Z, Kjetland EF. Exploring the feasibility and possible efficacy of mass treatment and education of young females as schistosomiasis influences the HIV epidemic. Arch Gynecol Obstet 2009; 281:455-60. [DOI: 10.1007/s00404-009-1108-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Accepted: 04/23/2009] [Indexed: 11/27/2022]
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Abstract
SUMMARYWe present a discrete time model for age-related changes in the mean and variance of the number of helminth parasites per host. We assess the degree of aggregation as the negative binomial parameter, k, and use the model to examine the influence of various factors on changes in aggregation with host age: discrete versus continuous infection; the degree of predisposition to infection; infection rate; parasite survival rate; and the variance in exposure to infective stages. The model can produce both increases and decreases in k with host age. However, with parameter values typical of many human helminth infections, a monotonic increase in k (decrease in aggregation) with age is predicted. With an age-dependent infection rate, convex relationships between k and age are possible. These predictions are consistent with data from field studies, but differ from those of previous models which have suggested that k is independent of host age in the absence of density dependence in parasite population dynamics. Differences between the models, and some difficulties in the interpretation of field data, are discussed.
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Kjetland EF, Kurewa EN, Ndhlovu PD, Midzi N, Gwanzura L, Mason PR, Gomo E, Sandvik L, Mduluza T, Friis H, Gundersen SG. Female genital schistosomiasis - a differential diagnosis to sexually transmitted disease: genital itch and vaginal discharge as indicators of genitalSchistosoma haematobiummorbidity in a cross-sectional study in endemic rural Zimbabwe. Trop Med Int Health 2008; 13:1509-17. [DOI: 10.1111/j.1365-3156.2008.02161.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Rudge JW, Stothard JR, Basáñez MG, Mgeni AF, Khamis IS, Khamis AN, Rollinson D. Micro-epidemiology of urinary schistosomiasis in Zanzibar: Local risk factors associated with distribution of infections among schoolchildren and relevance for control. Acta Trop 2008; 105:45-54. [PMID: 17996207 DOI: 10.1016/j.actatropica.2007.09.006] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2007] [Revised: 09/17/2007] [Accepted: 09/26/2007] [Indexed: 10/22/2022]
Abstract
Although it is well recognised that both behavioural and environmental factors play a role in determining small-scale heterogeneities in schistosomiasis transmission, empirical evidence of their relative importance is often limited. A study was conducted around Chaani, a village in northern Unguja (Zanzibar) where urinary schistosomiasis is endemic, in order to shed light upon the micro-epidemiology of Schistosoma haematobium and patterns of infection within schoolchildren and the intermediate host snail Bulinus globosus, that may help in adjusting recently implemented control programmes. Malacological surveys were conducted to identify transmission foci and questionnaires were devised to assess recalled water-contact patterns of 150 schoolchildren who had been screened for S. haematobium infection, finding an overall prevalence of 50.6%. Boys were more frequently and more heavily infected than girls and, accordingly, mean exposure scores were significantly higher for boys than girls. Univariate statistics revealed significant associations between infection and specific water-contact activities, including washing/bathing (odds ratio [OR]=3.01, 95% confidence interval [CI]=1.36-6.67) and playing (OR=4.03, 95% CI=1.51-10.70) in streams/ponds. In multivariate analysis, however, the strongest predictor of infection was proximity of the child's home to a site harbouring S. haematobium-infected B. globosus (P<0.001), suggesting that geography may be a better proxy for exposure than self-reported water contact. Surveillance programmes may therefore wish to prioritise evaluation of environmental risk to pinpoint transmission at the micro-geographical level, although water-contact questionnaires are also recommended as a complementary tool to rapidly identify the behaviour patterns of children at most risk of infection in the rural communities of Zanzibar. Such knowledge is a prerequisite for focusing and improving schistosomiasis control at the local level.
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Seto EYW, Lee YJ, Liang S, Zhong B. Individual and village-level study of water contact patterns and Schistosoma japonicum infection in mountainous rural China. Trop Med Int Health 2007; 12:1199-209. [PMID: 17956502 DOI: 10.1111/j.1365-3156.2007.01903.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE To describe the exposure patterns related to schistosomiasis transmission in 10 villages in rural Xichang County, Sichuan, China. METHODS Individual and village-level study of water contact exposure and Schistosoma japonicum reinfection; after initial infection survey and treatment, reinfection was determined 2 years later for 1604 individuals, of whom 578 also participated in a cross-sectional survey to assess their water contact behaviours. RESULTS The highest intensity of reinfection was observed in farmers aged 20-29 years, with no difference between sexes. While water contact measured as m(2)-minutes of contact was not associated with reinfection, an exposure metric computed by spatially weighting water contact by cercarial risk was correlated with both infection status and intensity. Village-level indicators based on snail density, number of infected snails, mouse bioassay data, and averaged individual-level exposures were associated with village reinfection rates. CONCLUSION Age-acquired immunity may be present in this population, but the study lacked sufficient power to discern differences in the exposure infection relationship with age.
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Affiliation(s)
- Edmund Y W Seto
- School of Public Health, University of California, Berkeley, CA 94720, USA.
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30
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Pinot de Moira A, Fulford AJC, Kabatereine NB, Kazibwe F, Ouma JH, Dunne DW, Booth M. Microgeographical and tribal variations in water contact and Schistosoma mansoni exposure within a Ugandan fishing community. Trop Med Int Health 2007; 12:724-35. [PMID: 17550469 DOI: 10.1111/j.1365-3156.2007.01842.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
OBJECTIVE To explore patterns of water contact and Schistosoma mansoni exposure by age, sex, tribe and space within a single village. METHODS For 10 months, we systematically observed water contacts made by the 800 inhabitants of a small Ugandan fishing village. In order to estimate cercarial exposure, times spent in water were weighted by snail infection levels, time of day and degree of immersion. RESULTS There were marked differences in water contact patterns between the two main tribes, which inhabited geographically distinct ends of the village resulting in geographically distinct spatial patterns of water contact. The distributions of the intermediate hosts, Biomphalaria sudanica and Biomphalaria stanleyi, also appeared to differ over small distances. This led to quite different exposure patterns between the two tribes, particularly amongst females. CONCLUSIONS Schistosoma mansoni exposure can vary markedly within a single village. Such non-homogenous patterns of exposure are likely to have wider implications for schistosomiasis control programmes and research studies.
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31
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Raso G, Vounatsou P, McManus DP, N’Goran EK, Utzinger J. A Bayesian approach to estimate the age-specific prevalence of Schistosoma mansoni and implications for schistosomiasis control. Int J Parasitol 2007; 37:1491-500. [PMID: 17583713 PMCID: PMC2756495 DOI: 10.1016/j.ijpara.2007.05.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2007] [Revised: 04/28/2007] [Accepted: 05/01/2007] [Indexed: 10/26/2022]
Abstract
Models that accurately estimate the age-specific infection prevalence of Schistosoma mansoni can be useful for schistosomiasis control programmes, particularly with regard to whether mass drug administration or selected treatment should be employed. We developed a Bayesian formulation of an immigration-death model that has been previously proposed, which used maximum likelihood inference for estimating the age-specific S. mansoni prevalence in a dataset from Egypt. For comparative purposes, we first applied the Bayesian formulation of the immigration-death model to the dataset from Egypt. We further analysed data obtained from a cross-sectional parasitological survey that determined the infection prevalence of S. mansoni among 447 individuals in a village in Côte d'Ivoire. Three consecutive stool samples were collected from each participant and analysed by the Kato-Katz technique. In the Côte d'Ivoire study, the observed S. mansoni infection prevalence was 41.6% and varied with age. The immigration-death model was able to correctly predict 50% of the observed age group-specific point prevalences. The model presented here can be utilized to estimate S. mansoni community infection prevalences, which in turn helps in the strategic planning of schistosomiasis control.
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Affiliation(s)
- Giovanna Raso
- Molecular Parasitology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia
- School of Population Health, The University of Queensland, Brisbane, Australia
- Corresponding author. Address: Molecular Parasitology Laboratory, Queensland Institute of Medical Research, 300 Herston Road, Herston, Qld 4006, Australia. Tel.: +61 7 3362 0406; fax: +61 7 3362 0104.
| | - Penelope Vounatsou
- Department of Public Health and Epidemiology, Swiss Tropical Institute, Basel, Switzerland
| | - Donald P. McManus
- Molecular Parasitology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia
| | - Eliézer K. N’Goran
- Unités de Formation et de Recherche des Biosciences, Université d’Abidjan-Cocody, Abidjan, Côte d’Ivoire
- Centre Suisse de Recherches Scientifiques, Abidjan, Côte d’Ivoire
| | - Jürg Utzinger
- Department of Public Health and Epidemiology, Swiss Tropical Institute, Basel, Switzerland
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32
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Kjetland EF, Mduluza T, Ndhlovu PD, Gomo E, Gwanzura L, Midzi N, Mason PR, Friis H, Gundersen SG. Genital schistosomiasis in women: a clinical 12-month in vivo study following treatment with praziquantel. Trans R Soc Trop Med Hyg 2006; 100:740-52. [PMID: 16406034 DOI: 10.1016/j.trstmh.2005.09.010] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2005] [Revised: 09/14/2005] [Accepted: 09/14/2005] [Indexed: 12/01/2022] Open
Abstract
Urinary schistosomiasis is known to be associated with lesions in the female genital organs, particularly with the presence of 'sandy patches' in the lower genital tract. This study sought to determine the effect of treatment with praziquantel on gynaecological schistosomiasis in residents of an area endemic for Schistosoma haematobium. A cohort study was conducted among women aged 20-49 years in rural Zimbabwe. The shape and size of lesions were mapped pre treatment and 3 and 12 months following treatment. Ova of S. haematobium were looked for in cytology smears, wet mounts, biopsies, urine and stool. Specimens were collected for detection of sexually transmitted diseases and cancer. At baseline, almost half of the 527 women included in the study had sandy patches. Although urinary ova excretion decreased following treatment (odds ratio 10.3, 95% CI 3.8-27.8, P<0.001), praziquantel treatment was not associated with a significant reduction in genital lesions or contact bleeding (P=0.31-0.94). Sandy patches remained strongly associated with contact bleeding and vessel abnormalities even after treatment. Findings were independent of HIV status. Such lesions, which are common and apparently refractory to treatment for at least 12 months, may be an important risk factor for both the acquisition and transmission of HIV.
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Affiliation(s)
- Eyrun F Kjetland
- Centre for Imported and Tropical Diseases, Department of Infectious Diseases, Ullevaal University Hospital, 0407 Oslo, Norway.
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Abstract
The canid intestinal immune system recognizes the cestode parasite Echinococcus following infection, but it is still unclear the extent to which protection against reinfection occurs. An increasing number of studies have shown that there are convex age-related abundance or prevalence rates in naturally infected populations of dogs with E. granulosus and foxes infected with E. multilocularis. Data from dogs naturally infected with E. granulosus give a better fit to a model that incorporates herd immunity compared to competing models of age-related changes in infection pressure. A theoretical framework suggests that such herd immunity will act as a stabilizing force for Echinococcus populations. Hence a decrease in infection pressure to dogs or foxes will not result in a corresponding decrease in infection pressure to intermediate hosts or to humans. In addition the age structure of the canid population could affect transmission.
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Affiliation(s)
- P R Torgerson
- WHO Collaborating Centre for Parasitic Zoonoses, Institute of Parasitology, University of Zürich, Winterthurestrasse 266a, Zürich, Switzerland.
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34
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Abstract
Analyses of contact-tracing data on the spread of infectious disease, combined with mathematical models, show that control measures require better knowledge of variability in individual infectiousness. From Typhoid Mary to SARS, it has long been known that some people spread disease more than others. But for diseases transmitted via casual contact, contagiousness arises from a plethora of social and physiological factors, so epidemiologists have tended to rely on population averages to assess a disease's potential to spread. A new analysis of outbreak data shows that individual differences in infectiousness exert powerful influences on the epidemiology of ten deadly diseases. SARS and measles (and perhaps avian influenza) show strong tendencies towards ‘superspreading events’ that can ignite explosive epidemics — but this same volatility makes outbreaks more likely to fizzle out. Smallpox and pneumonic plague, two potential bioterrorism agents, show steadier growth but still differ markedly from the traditional average-based view. These findings are relevant to how emerging diseases are detected and controlled.
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Affiliation(s)
- Alison P. Galvani
- the Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, 06520 Connecticut USA
| | - Robert M. May
- the Department of Zoology, University of Oxford, Oxford, OX1 3PS UK
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35
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Woolhouse ME. Immunoepidemiology of human schistosomes: taking the theory into the field. ACTA ACUST UNITED AC 2005; 10:196-202. [PMID: 15275473 DOI: 10.1016/0169-4758(94)90030-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Much is known about human immune responses to schistosome infection, but it has proved difficult to determine the impact of these responses on schistosome epidemiology in the field. In this paper, Mark Woolhouse compares epidemiological patterns from field data with the predictions o f simple mathematical models of different immunological processes. The comparison gives some indications as to which types of immune response may be important, and of their strength and duration. The results are consistent with a significant impact of a process similar to 'concomitant' immunity, with a possible role for anti-fecundity effects.
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Affiliation(s)
- M E Woolhouse
- Department of Zoology, University of Oxford, South Parks Road, Oxford, UK OX I 3PS
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36
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Poggensee G, Krantz I, Nordin P, Mtweve S, Ahlberg B, Mosha G, Freudenthal S. A six-year follow-up of schoolchildren for urinary and intestinal schistosomiasis and soil-transmitted helminthiasis in Northern Tanzania. Acta Trop 2005; 93:131-40. [PMID: 15652327 DOI: 10.1016/j.actatropica.2004.10.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2004] [Revised: 10/18/2004] [Accepted: 10/27/2004] [Indexed: 11/29/2022]
Abstract
Two cross-sectional studies with a 6-year interval were undertaken in two primary schools in neighbouring villages in Mwanga District, Tanzania, to determine the prevalence of schistosome and soil-transmitted helminth infections before and 6 years after treatment. Within this interval, health-related interventions such as one mass treatment of the villagers, health education, improvement of sanitation and access to safe water were undertaken in the villages. In 1996, urinary schistosomiasis occurred in Kileo (n=284) and Kivulini (n=350) in 37.0 and 86.3% of the schoolchildren. Intestinal schistosomiasis was found in 22.9 and 43.5% of the children. The infection with soil-transmitted helminths ranged between 2.7 and 18.1% in both villages. After 6 years, the prevalence of urinary schistosomiasis in schoolchildren remained nearly constant in Kileo (33.5%; n=544), but dropped from 86.3% to 70.0% in Kivulini (n=514). In the latter village the proportion of children heavily infected with Schistosoma haematobium (> or = 50 eggs/10 ml urine) decreased from 53.8% to 34.4%. With the exception of hookworm infection, soil-transmitted helminthiasis and intestinal schistosomiasis were significantly less seen in 2002 compared to the baseline. The previous chemotherapy of schoolchildren and villagers in 1996 and 1998, respectively, might have led to a reduced transmission of schistosomiasis in the following years. However, the reduction of prevalence of soil-transmitted helminthiasis is more likely to be the result of health-related interventions.
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Affiliation(s)
- Gabriele Poggensee
- Department Infectious Disease Epidemiology, Robert Koch-Institute, Seestrasse 10, 13353 Berlin, Germany.
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37
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Bethony J, Williams JT, Brooker S, Gazzinelli A, Gazzinelli MF, LoVerde PT, Corrêa-Oliveira R, Kloos H. Exposure to Schistosoma mansoni infection in a rural area in Brazil. Part III: household aggregation of water-contact behaviour. Trop Med Int Health 2004; 9:381-9. [PMID: 14996368 DOI: 10.1111/j.1365-3156.2004.01203.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Much research points to the importance of the household in the study of water-borne diseases such as schistosomiasis. An important aspect of the household is the clustering of domestic activities associated with water collection, storage and usage. Such activities can result in the sharing of water-contact sites and water-contact behaviour, which expose household members to similar risks of infection. In previous studies, we determined that shared residence accounted for 28% of the variance in Schistosoma faecal egg excretion rates. We now quantify the effect of shared residence on the variation in water-related health behaviours. We found that shared residence accounted for 30% of the variation in total water contacts per week. It also accounted for a large proportion of the variation in individual water-contact behaviour: e.g. agricultural contacts (63%), washing limbs (56%) or bathing (41%). These results implicate the household as an important composite measure of the complex relationships between socioeconomic, environmental and behavioural factors that influence water-contact behaviour and, therefore, the transmission of schistosomiasis. Our results also support a focus on the household in the implementation of schistosomiasis prevention and control efforts.
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Affiliation(s)
- Jeffrey Bethony
- Department of Microbiology & Tropical Medicine, The George Washington University Medical Center, Washington, DC 20037, USA.
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38
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Abstract
The effects of using different methods to calculate individual infection intensities on the age-infection distribution of Schistosoma mansoni field data are demonstrated. Methods are tested on a maximum of three stool samples per person collected on three consecutive days; the methods considered for the calculation of individual infection intensities are the geometric mean (GM), arithmetic mean (AM) and pseudo geometric mean (GM of stool samples instead of replicates). In addition, the effects of calculating the infection intensity for each age group using either AMs or GMs are compared. Differences occur in the shape of the age-infection profiles obtained by using either the arithmetic or geometric group mean. When using the AM, peak infection intensity occurs in a younger age group compared to using the GM, and all three methods of calculating individual infection intensity give the first peak of infection in the same age group. However, differences occur in the position of the second peak which occurs earlier with the two GMs than with the AM. Bootstrapping procedures show that the individual AM, gives a different age group for the first peak of infection at least 25% of the time when compared to either of the GMs, and 31% of the time for the second peak, while the two GMs give the same peak age groups around 90-92% of the time for both peaks. When using the GM, to calculate infection intensity for each age group, there are no differences between the three methods used to calculate individual infection intensity. This is confirmed by bootstrapping procedures. The results are discussed in relation to the distribution of parasites and levels of parasite aggregation. The implications of the results for field studies are also discussed.
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Affiliation(s)
- F Mutapi
- Birkbeck College, University of London, Malet St. Bloomsbury, London WC1E 7HX, UK.
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39
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Yang HM. Comparison between schistosomiasis transmission modelings considering acquired immunity and age-structured contact pattern with infested water. Math Biosci 2003; 184:1-26. [PMID: 12788231 DOI: 10.1016/s0025-5564(03)00045-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In order to analyze the effects of acquired immunity and the contact pattern with infested water on the overall transmission of schistosomiasis, a semi-stochastic model is proposed. The model's assumptions are the simplest possible to enhance the differences between two hypotheses. With respect to the human host, it is assumed the mounting of an immune response after elapsing a fixed period of time L from the first infection, which is partially effective and never lost. With respect to the contact pattern with infested water, it is assumed a decreasing age-related function. Both models are compared to a purely random model, which is taken as the basic model.
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Affiliation(s)
- Hyun Mo Yang
- Universidade Estadual de Campinas, IMECC, Departamento de Matemática Aplicada, Caixa Postal 6065 CEP, Campinas, Sao Paulo 13081-970, Brazil.
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40
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Scott JT, Diakhaté M, Vereecken K, Fall A, Diop M, Ly A, De Clercq D, de Vlas SJ, Berkvens D, Kestens L, Gryseels B. Human water contacts patterns in Schistosoma mansoni epidemic foci in northern Senegal change according to age, sex and place of residence, but are not related to intensity of infection. Trop Med Int Health 2003; 8:100-8. [PMID: 12581433 DOI: 10.1046/j.1365-3156.2003.00993.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In an epidemic focus in northern Senegal, adults had lower intensities of infection than adolescents, a phenomenon that could not be attributed to immunity acquired over the previous 10-15 years of exposure to the parasite because all age groups had had the same number of years' experience of the worm. This article considers whether this pattern could have been because of higher levels of exposure to the parasite in younger age groups. Personal contact with infected water was recorded using a questionnaire in Schistosoma mansoni foci not more than 3 years old and in another, 10-year-old focus. Many aspects of contact (e.g. frequency, duration or time of day of contact) may contribute to the number of encounters with infective cercariae (true exposure), so various assumptions regarding the relationship between water contact and true exposure were tested resulting in a range of exposure indices. People reported a mean of 4.4 separate contacts, and spent a median of 57 min per day in water. Patterns of water contact differed depending on the exposure index used, e.g. considering duration, males spent a longer time in water than females (P < 0.001). But using frequency, females had more contacts with water than males in most villages (P < 0.001). Generally, exposure levels dropped as people become aged (P < 0.001) and residents of the older focus were more exposed than residents of other foci (P < 0.002). Intensity of (re)infection was not related to exposure either alone or in models incorporating age, sex and/or village irrespective of the index used. There is therefore evidence that age, sex and place of residence determine exposure but none to suggest that exposure had an influence on the relationship between these factors and intensity of infection. We propose therefore that in this population other factors have principal importance in determining intensity of infection.
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Affiliation(s)
- J T Scott
- Institute of Tropical Medicine, Antwerp, Belgium.
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41
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Mutapi F, Roddam A. p values for pathogens: statistical inference from infectious-disease data. THE LANCET. INFECTIOUS DISEASES 2002; 2:219-30. [PMID: 11937422 DOI: 10.1016/s1473-3099(02)00240-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Certain features of infectious-disease data-including the aggregated nature of the data, confounding variables, correlated variables, and non-linear relations-complicate the use of standard statistical procedures. Using data on a helminth infection, we review the use of three parametric tests (analysis of variance, linear regression, and logistic regression), address the complications arising from violation of the assumptions for these tests, and suggest methods of correction. We also compare the relative merits of parametric methods with equivalent non-parametric approaches, and illustrate the differences produced with results from a Kruskal-Wallis test and a t test. The value of using a resampling method-bootstrapping-is also shown. Finally, we discuss problems arising from use of a study design that requires data on the same attribute to be collected from the same individual over a period of time, and present three methods for overcoming this complication, showing that, in the example used, the mixed effect model and generalised estimating equation give similar results.
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Affiliation(s)
- Francisca Mutapi
- Section of Comparative Epidemiology and Informatics, Department of Veterinary Clinical Studies, University of Glasgow Veterinary School, Glasgow, UK.
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42
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Friedman JF, Kurtis JD, McGarvey ST, Fraga AL, Silveira A, Pizziolo V, Gazzinelli G, LoVerde P, Corrêa-Oliveira R. Comparison of self-reported and observed water contact in an S. mansoni endemic village in Brazil. Acta Trop 2001; 78:251-9. [PMID: 11311188 DOI: 10.1016/s0001-706x(01)00094-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Estimates of exposure are critical for immuno-epidemiologic and intervention studies in human schistosomiasis. Direct observation of human water contact patterns is both costly and time consuming. To address these issues, we determined whether individuals residing in a Schistosoma mansoni endemic village in Brazil could accurately self-report their water contact patterns. We compared the results of a water contact questionnaire to the present gold standard, direct observation of water contact in 86 volunteers, aged 8--29. We administered a survey to estimate volunteers' frequency and type of water contact and directly measured each volunteers' water contact patterns during 5 weeks of detailed water contact observations. We found a poor correlation between self reported frequency of contact and directly observed exposure (rho=0.119, P=NS). The questionnaire data was supplemented by information about average body surface area of exposure and duration of contact for specific activities derived from observations of this cohort. This 'supplemented questionnaire' data was significantly correlated with their exposure index (rho=0.227, P=0.05). It provides a starting point from which questionnaires may develop to provide a more cost-effective and less labor intensive method of assessing water contact exposure at the level of the individual.
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Affiliation(s)
- J F Friedman
- International Health Institute, Brown University, Box G-B497, Providence, RI 02912, USA.
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43
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Gazzinelli A, Bethony J, Fraga LA, LoVerde PT, Correa-Oliveira R, Kloos H. Exposure to Schistosoma mansoni infection in a rural area of Brazil. I: water contact. Trop Med Int Health 2001; 6:126-35. [PMID: 11251909 DOI: 10.1046/j.1365-3156.2001.00684.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The study of water contact patterns in rural Brazil presents unique challenges due to widely dispersed settlement patterns, the ubiquity of water contact sites, and the privatization of water resources. This study addresses these challenges by comparing the two most widely used methods of assessing water contact behaviour: direct observation and survey. The results of a 7-day direct observation of water contact were compared with water contact surveys administered 1 week after and then 1 year after the direct observation study. The direct observation study recorded a water contact rate higher than reported by other investigators (3.2 contacts per person per day); however, 75% of these contacts were for females and consisted mainly of domestic activities occurring around the household. A comparison of the frequency of water contact activities between the direct observation and the two surveys revealed several important points. First, no significant differences were found between methods for routine water contact activities (e.g. bathing), indicating that participants were able to accurately self-report some types of water contact activities. Second, significant differences were found in the recording of water contact activities that took place outside the observation area, indicating that direct observation may under-report water contact activities in areas where contact sites are dispersed widely. Third, significant differences between the direct observation and the survey method were more common for males than for females, indicating that the combination of widespread water contact sites and gender-specific division of labour may result in under-reporting of male contacts by direct observation methods. In short, despite the limitations in the recording of duration and body exposure, the survey method may more accurately record the frequency of water contact activities than direct observation methods in areas of widely dispersed water contact sites. Hence, surveys may be more suitable for the unique challenges of water contact in rural areas of Brazil.
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Affiliation(s)
- A Gazzinelli
- Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
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44
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Yang HM, Yang AC. The stabilizing effects of the acquired immunity on the schistosomiasis transmission modeling--the sensitivity analysis. Mem Inst Oswaldo Cruz 1999; 93 Suppl 1:63-73. [PMID: 9921325 DOI: 10.1590/s0074-02761998000700009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A mathematical model is proposed to analyze the effects of acquired immunity on the transmission of schistosomiasis in the human host. From this model the prevalence curve dependent on four parameters can be obtained. These parameters were estimated fitting the data by the maximum likelihood method. The model showed a good retrieving capacity of real data from two endemic areas of schistosomiasis: Touros, Brazil (Schistosoma mansoni) and Misungwi, Tanzania (S. haematobium). Also, the average worm burden per person and the dispersion of parasite per person in the community can be obtained from the model. In this paper, the stabilizing effects of the acquired immunity assumption in the model are assessed in terms of the epidemiological variables as follows. Regarded to the prevalence curve, we calculate the confidence interval, and related to the average worm burden and the worm dispersion in the community, the sensitivity analysis (the range of the variation) of both variables with respect to their parameters is performed.
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Affiliation(s)
- H M Yang
- Departamento de Matemática Aplicada/IMECC, Universidade Estadual de Campinas, SP, Brasil.
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45
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Ross AG, Yuesheng L, Sleigh AC, Williams GM, Hartel GF, Forsyth SJ, Yi L, McManus DP. Measuring exposure to S. japonicum in China. I. Activity diaries to assess water contact and comparison to other measures. Acta Trop 1998; 71:213-28. [PMID: 9879732 DOI: 10.1016/s0001-706x(98)00063-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
We introduce a new method, activity diaries, in order to evaluate human water contact among fishing communities in an area moderately endemic for Schistosoma japonicum in the Dongting Lake region of Southern China. Two hundred and forty-nine subjects (76% male) were followed prospectively over a 9-month-period in order to verify exposure and reinfection. Exposure was determined crudely with questionnaires, direct 12-h water observations, and more precisely with activity diaries and an adjusted exposure model which took into account the time of day, the duration of contact and the percent body surface area in contact with water. Cohort subjects filled in activity diaries for an average of 85 days as compared with 2 days for the direct water observations. The typical unadjusted mean daily water contact (duration) based on the activity diaries was 53 min with 62% of this time spent in fishing. In contrast, the direct water observations revealed an average daily duration of 149 min with 53% of the time spent in fishing. Human water contact patterns (min/day) by site, activity and body part exposed were examined with the activity diaries. Individuals in the 36-49-year-old age range had the highest degree of water contact. Most of this daily contact occurred by males on the hands (mean+/-S.D.; 83.53+/-67.80 min/day) while fishing (mean+/-S.D.; 87.84+/-8.88 min/day) on the lake (mean+/-S.D.; 85.98+/-69.90 min/day). There was a strong positive log correlation (r=0.95) between the crude and adjusted (based on our derived exposure model) diary outcomes for the entire study sample, however, at higher exposure levels this relationship was differentially weaker (r=0.70). Results from this study suggest that current methods used in evaluating schistosomiasis exposure in China may overestimate and bias measures of the risk of infection. Activity diaries adjusted for the time of day, duration and the percent body surface area exposed are cost-effective and practical instruments to accurately quantify human exposure in the vast lake regions of Southern China where most of the endemic schistosomiasis japonica occurs.
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Affiliation(s)
- A G Ross
- Tropical Health Program, Australian Centre for International and Tropical Health and Nutrition, The University of Queensland and The Queensland Institute of Medical Research, Herston, Brisbane
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46
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Woolhouse ME, Dye C, Etard JF, Smith T, Charlwood JD, Garnett GP, Hagan P, Hii JL, Ndhlovu PD, Quinnell RJ, Watts CH, Chandiwana SK, Anderson RM. Heterogeneities in the transmission of infectious agents: implications for the design of control programs. Proc Natl Acad Sci U S A 1997; 94:338-42. [PMID: 8990210 PMCID: PMC19338 DOI: 10.1073/pnas.94.1.338] [Citation(s) in RCA: 775] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/1996] [Accepted: 10/07/1996] [Indexed: 02/03/2023] Open
Abstract
From an analysis of the distributions of measures of transmission rates among hosts, we identify an empirical relationship suggesting that, typically, 20% of the host population contributes at least 80% of the net transmission potential, as measured by the basic reproduction number, R0. This is an example of a statistical pattern known as the 20/80 rule. The rule applies to a variety of disease systems, including vector-borne parasites and sexually transmitted pathogens. The rule implies that control programs targeted at the "core" 20% group are potentially highly effective and, conversely, that programs that fail to reach all of this group will be much less effective than expected in reducing levels of infection in the population as a whole.
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Affiliation(s)
- M E Woolhouse
- Wellcome Trust Centre for the Epidemiology of Infectious Disease, Department of Zoology, University of Oxford, United Kingdom.
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47
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Fulford AJ, Ouma JH, Kariuki HC, Thiongo FW, Klumpp R, Kloos H, Sturrock RF, Butterworth AE. Water contact observations in Kenyan communities endemic for schistosomiasis: methodology and patterns of behaviour. Parasitology 1996; 113 ( Pt 3):223-41. [PMID: 8811848 DOI: 10.1017/s0031182000082007] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A descriptive analysis of observed water contact activities in seven Kenyan (Akamba) communities is presented. The patterns of contact with time of day, month of year, type of activity, degree of immersion, use of soap, use of 'kithima' and day of week are all considered, with particular attention given to how these vary with age and sex. It is noted that (a) patterns of contact vary dramatically between these culturally rather similar communities, (b) contact usually peaks in the second decade of life, (c) generally females, especially young women, spend more time at the water than males and (d) simple (unweighted) total observed duration of contact gives a relatively inflated estimate of exposure in adults, especially young women. The methodology of observation and data handling is described in some detail.
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Affiliation(s)
- A J Fulford
- Department of Pathology, University of Cambridge, UK.
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48
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Woolhouse ME, Hasibeder G, Chandiwana SK. On estimating the basic reproduction number for Schistosoma haematobium. Trop Med Int Health 1996; 1:456-63. [PMID: 8765453 DOI: 10.1046/j.1365-3156.1996.d01-88.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Existing estimates of the basic reproduction number, Ro, for human schistosomes are mostly in the range 1-4, implying that schistosomes should be relatively easy to eliminate from endemic areas, which is contrary to practical experience. An estimate of Ro for a site in Zimbabwe is obtained here using a mathematical model explicitly incorporating two features believed to be epidemiologically significant; age-dependent exposure and acquired immunity. Parameter estimates are, as far as possible, obtained independently, but the coefficients representing man-snail and snail-man transmission, as well as parameters representing effects of acquired immunity, must be estimated indirectly by fitting the model to field data. Heterogeneity in human exposure and contamination is crudely incorporated by considering "wormy' and non-wormy' fractions of the population. The results suggest Ro to be in the range 4-5 or more, higher than previous estimates and despite only moderate levels of infection at this site. It is shown that this estimate is sensitive to the form of the underlying model. The application of less realistic models may lead to less reliable estimates of Ro.
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49
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Palmer DR, Hall A, Haque R, Anwar KS. Antibody isotype responses to antigens of Ascaris lumbricoides in a case-control study of persistently heavily infected Bangladeshi children. Parasitology 1995; 111 ( Pt 3):385-93. [PMID: 7567106 DOI: 10.1017/s0031182000081944] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Antibody responses to Ascaris lumbricoides worm antigens were examined by ELISA in a case-control study of 2 groups of Bangladeshi children, one of which had been shown over a period of 12 months to be consistently lightly infected (controls) and the other consistently heavily infected (cases). The children showed a wide range in intensity of infection; children identified as cases were on average 4 times more heavily infected than the controls. There were no significant differences in weight, height, mid-upper arm circumference and skinfold thickness between the case or control subjects at the time blood samples for analyses by ELISA were collected. Children with repeatedly heavy infections with A. lumbricoides had higher concentrations of antibody isotypes to the antigens of A. lumbricoides than children who are repeatedly lightly infected. IgG1, IgG4 and IgE to worm antigens occurred in significantly higher concentrations in heavily infected subjects. This suggests that these antibody responses simply reflect the intensity of infection and may not play a significant role in protecting against heavy infections.
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Affiliation(s)
- D R Palmer
- Department of Biology, Imperial College, London, UK
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50
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Woolhouse ME, Ndamba J, Bradley DJ. The interpretation of intensity and aggregation data for infections of Schistosoma haematobium. Trans R Soc Trop Med Hyg 1994; 88:520-6. [PMID: 7992326 DOI: 10.1016/0035-9203(94)90144-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The relationships between mean intensities of infection, the aggregation of infection among hosts, and host age are analysed using data from 2 large (> 3000 individuals) field studies of Schistosoma haematobium infection. The data show a convex relationship between mean intensity and age, a convex relationship between an inverse index of aggregation and age, and an age-dependent relationship between the mean and aggregation of infection intensity when levels of infection are high. These patterns are qualitatively compared with the output of mathematical models based on an immigration-death process (model I), and incorporating age-dependent changes in the distribution of exposure to infection as suggested by field data (model II), or reductions in the rate of infection as a function of either current (model III) or cumulative (model IV) parasite burdens, that is, density-dependent processes without or with memory, respectively. Models II and III were able to reproduce observed patterns, but model IV, which is a possible representation of acquired immunity, was not. These results are consistent with the following assumptions: (i) age-related patterns of aggregation can be generated without recourse to density-dependent processes; (ii) the epidemiological impact of density-dependent processes depends on whether these act with or without memory; and (iii) any acquired immunity to human S. haematobium infection may be significantly less than life-long.
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