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A Field-Based Modelling Framework of the Ecohydrology of Schistosomiasis

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A Field-Based Modelling Framework of the Ecohydrology of Schistosomiasis $ÀHOGEDVHGPRGHOOLQJIUDPHZRUNRIWKHHFRK\GURORJ\RI VFKLVWRVRPLDVLV THÈSE NO 8239 (2018) PRÉSENTÉE LE 16 FÉVRIER 2018 À LA FACULTÉ DE L'ENVIRONNEMENT NATUREL, ARCHITECTURAL ET CONSTRUIT LABORATOIRE D'ÉCOHYDROLOGIE PROGRAMME DOCTORAL EN GÉNIE CIVIL ET ENVIRONNEMENT ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE POUR L'OBTENTION DU GRADE DE DOCTEUR ÈS SCIENCES PAR Francisco Javier PEREZ SAEZ acceptée sur proposition du jury: Prof. T. I. Battin, président du jury Prof. A. Rinaldo, directeur de thèse Prof. J. Utzinger, rapporteur Prof. J. Remais, rapporteur Prof. M. Salathé, rapporteur Suisse 2018 Il vaut mieux avoir de la poussière aux pieds, que de l’avoir aux fesses. — Proverbe africain Acknowledgements I would like to thank Andrea Rinaldo for the opportunity he has given me to embark on this thesis, for his culture of curiosity-driven research, and for guidance and advice throughout the years. This thesis would not have been possible without the financial support of the Swiss Agency for Development and Cooperation through the Projet 3E Afrique, Burkina Faso-2iE partie scientifique. I was fortunate to share this research journey with Théophile Mande the whole way through, from whom I learned a great deal about Burkina Faso, science and life more in general. I am also grateful for the guidance of Natalie Ceperley during the first year of the thesis, and all the open-minding chats since then. I thank Lorenzo Mari and Enrico Bertuzzo for their support and for insightful discussions. These four years have been rich not only on the scientific plane, but also at the personal level, and for this I must thank the whole ECHO lab for its fantastic working environment and for the fact that I have learned something from each and every one of its members: from Pierre the taste for outdoors and exploration, may it be in the ruggedness of the Alps or of Ouagadougou’s streets; from Flavio that deepness of thought is not (always) contradictory with lightness of spirit, and attain their greatest harmony in the act of skiing; from Jean-Marc navigation techniques in the meanders of international cooperation; from Anna the value of communication and listening; from Bernard what being a field hydrologist is all about, as opposed to the "salon" hydrologists that can be found these days; from Andrea (G.) that with great power, must come great bravery, which with great modesty, give great Jungle Speed players; from Silvia what a real piadina tastes like, how science and art find their way to mingle, and, more importantly, that romanesco broccoli are not as innocuous as one may think; from Damiano I failed to learn juggling and shooting hoops, but I was able to learn from the way he made people smile, laugh, and brighten, even when singing questionable italian culinary songs; from Ana-Clara the marvels of the mix of paõ de queijo, kindness, and cachaça, with due slowness, of course; from Luca I wish I had been able to retain more of his encyclopedic knowledge about world capitals, cycling, and much more, but I have certainly learned about dedication and commitment, may it be to science or teaching; from Paolo the embracing panache of classroom teaching, the sparkle of varying moustache styles, and the importance of empathy in both these aspects of life, and beyond; from Joseph the craftsmanship of poised nonchalant humour, the infinite possible uses of "ohala", and the discovery of the Garamont font; and finally, from Jonathan I learned to unleash one’s creativity in unsuspected ways, across multiple media, and how valuable it is to have an outstanding office mate in shiny and less shiny days. I thank my family for their unconditional love and support. Finally I thank you Sophie for making it all have meaning. Lausanne, 1 February 2018 i Summary Successful control of schistosomiasis, a water-borne parasitic disease, is challenged by the intricacy of the worm’s lifecycle, which depends on aquatic snail intermediate hosts, and involves environmental, ecologic, and socio-economic factors. Current strategies rely on deworming through mass drug adminis- tration which however do not protect against reinfection and the persistence of hotspots. It is recognized that multifaceted approaches will be necessary to reach elimination, whose development will require a renewed focus on the disease’s social-ecological drivers. Taking cue from the hydrological underpinning of these drivers, this Thesis aims at developing an ecohydrological approach to schistosomiasis with a view to identifying and exploiting the points in which its cycle can be broken. Schistosomiasis is a poverty-reinforcing disease affecting more than 150 million people in sub-Saharan Africa, being the parasitic disease causing the largest health burden after malaria. However, the impairing morbidity it causes has been undervalued in the past, qualifying it as a neglected tropical disease. Moreover, water resources development often exacerbate transmission, posing scientific and ethical challenges in addressing the ensuing trade-off between economic development and public health. The relevance of this Thesis’ work lies in furthering tools to offset this trade-off by unlocking the predictive appraisal of the social-ecological drivers of transmission. An integration of fieldwork applied in Burkina Faso (West Africa) and theoretical methods are employed to address this aim. This Thesis establishes the use of spatially explicit mathematical models of schistoso- miasis at the national-scale, allowing to study the effect of human mobility and spatial heterogeneity of transmission parameters. Weekly ecological samplings of snail abundance and continuous environmen- tal monitoring were preformed at three sites along the country’s climatic gradient, leveraged through ecological modelling. A novel methodology for the large-scale prediction of river network ephemerality allowed for refined snail species distribution models, and the analysis of the disease’s geography in link with socio-economic covariates. Finally, surveys and participatory workshops shed light on local-scale water contact patterns. The obtained results substantiate the stance that hydrology is a first-order control of disease transmission. Stability analysis of the spatially explicit model generated additional insight into the impact of the expan- sion of suitable snail habitat due to water resources development, highlighting the interplay between local and country-wide effects driven by human mobility. Models of snail ecology revealed key hydrological drivers, and disputed density feedbacks. Uncovered phase shifts between permanent and ephemeral habitats were adequately reproduced at the national scale through model regionalization. Characteriza- tion and predictions of hydrological ephemerality improved the estimation of the snails’ ecological range, mirroring the disease’s geography. Finally a national-scale association between ephemerality and disease risk was observed, possibly due to human-water contacts aggregation, as supported by preliminary results at village-level. The future incorporation of these ecohydrological findings into spatially explicit models of schistosomiasis is considered promising for optimizing control strategies and attaining disease elimination. iii Summary Key words: schistosomiasis; ecohydrology; spatially explicit mathematical modelling; Burkina Faso; water resources development; hydrological ephemerality; iv Résumé Le succès du contrôle de la schistosomiase, une maladie d’origine hydrique, dépend de la capacité a agir sur la complexité du cycle de vie du parasite qui dépend d’escargots aquatiques comme hôtes intermédiaires, et implique des facteurs environnementaux, écologiques et socio-économiques. Les stratégies actuelles reposent l’administration de masse de médicaments qui, cependant, ne protègent pas contre la réinfection. Il est reconnu qu’une approches multisectorielles sera nécessaire pour éliminer la maladie, mais nécessitera une attention renouvelée sur ses aspects socio-écologiques. Misant sur le lien entre l’hydrologie et la transmission de la maladie, cette thèse vise à développer une approche écohydrologique de la schistosomiase en vue d’identifier et d’exploiter les levier pour interrompre sa transmission. La schistosomiase est une maladie affectant plus de 150 millions de personnes en Afrique subsaharienne. Cependant, la morbidité qui en découle a été sous-évaluée dans le passé. De plus, le développement des ressources en eau exacerbe souvent la transmission, ce qui pose des défis scientifiques et éthiques dans l’arbitrage qui s’ensuit entre le développement économique et la santé publique. Cette thèse vies donc aux développement d’outils pour dépasser ce compromis en comprenant mieux les facteurs socio- écologiques de la transmission. Une combinaison de travail de terrain au Burkina Faso (Afrique de l’Ouest) et d’outils théoriques a été utilisée pour atteindre ce but. Cette thèse établit l’utilisation de modèles mathématiques spatialement explicites de la schistosomiase à l’échelle nationale, permettant d’étudier l’effet de la mobilité humaine et de l’hétérogénéité spatiale des paramètres de transmission. Des échantillonnages écologiques de l’abondance des escargots ont été faits sur trois sites le long du gradient climatique du pays, mis à profit par la modélisation écologique. Une méthodologie novatrice pour la prédiction à grande échelle de l’éphéméralité du réseau fluvial a permis d’améliorer des modèles spatiaux de répartition des espèces d’escargots, et l’analyse de la géographie de la maladie en lien avec des
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