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  • 1
    Language: English
    Description: We report about field and theoretical studies on the ecology of the aquatic snails (Bulinus spp. and Biomphalaria pfeifferi) that serve as obligate intermediate hosts in the complex life cycle of the parasites causing human schistosomiasis. Snail abundance fosters disease transmission, and thus the dynamics of snail populations are critically important for schistosomiasis modeling and control. Here, we single out hydrological drivers and density dependence (or lack of it) of ecological growth rates of local snail populations by contrasting novel ecological and environmental data with various models of host demography. Specifically, we study various natural and man-made habitats across Burkina Faso’s highly seasonal climatic zones. Demographic models are ranked through formal model comparison and structural risk minimization. The latter allows us to evaluate the suitability of population models while clarifying the relevant covariates that explain empirical observations of snail abundance under the actual climatic forcings experienced by the various field sites. Our results link quantitatively hydrological drivers to distinct population dynamics through specific density feedbacks, and show that statistical methods based on model averaging provide reliable snail abundance projections. The consistency of our ranking results suggests the use of ad hoc models of snail demography depending on habitat type (e.g., natural vs. man-made) and hydrological characteristics (e.g., ephemeral vs. permanent). Implications for risk mapping and space-time allocation of control measures in schistosomiasis-endemic contexts are discussed.
    Keywords: Freshwater Snails Water-Based Disease Infection Controls Environmental Monitoring
    ISSN: 00278424
    E-ISSN: 10916490
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  • 2
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 27 November 2012, Vol.109(48), pp.19703-8
    Description: Understanding, predicting, and controlling outbreaks of waterborne diseases are crucial goals of public health policies, but pose challenging problems because infection patterns are influenced by spatial structure and temporal asynchrony. Although explicit spatial modeling is made possible by widespread data mapping of hydrology, transportation infrastructure, population distribution, and sanitation, the precise condition under which a waterborne disease epidemic can start in a spatially explicit setting is still lacking. Here we show that the requirement that all the local reproduction numbers R0 be larger than unity is neither necessary nor sufficient for outbreaks to occur when local settlements are connected by networks of primary and secondary infection mechanisms. To determine onset conditions, we derive general analytical expressions for a reproduction matrix G0, explicitly accounting for spatial distributions of human settlements and pathogen transmission via hydrological and human mobility networks. At disease onset, a generalized reproduction number Λ0 (the dominant eigenvalue of G0) must be larger than unity. We also show that geographical outbreak patterns in complex environments are linked to the dominant eigenvector and to spectral properties of G0. Tests against data and computations for the 2010 Haiti and 2000 KwaZulu-Natal cholera outbreaks, as well as against computations for metapopulation networks, demonstrate that eigenvectors of G0 provide a synthetic and effective tool for predicting the disease course in space and time. Networked connectivity models, describing the interplay between hydrology, epidemiology, and social behavior sustaining human mobility, thus prove to be key tools for emergency management of waterborne infections.
    Keywords: Disease Outbreaks ; Water Microbiology
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 3
    Language: English
    In: Oecologia, 2011, Vol.165(2), pp.333-339
    Description: Identifying factors and processes influencing natural mortality is fundamental to the understanding of population dynamics. Metabolic theory of ecology and experimental studies at the cross-species level suggest the existence of general patterns linking natural mortality to body mass and temperature. However, there is scant evidence that similar relationships also hold at the intra-specific scale, possibly because of the relatively narrow range of sizes and temperatures experienced by most species and the effect of local adaptation, which can obscure links between temperature and vital rates. In this sense, the European eel Anguilla anguilla , a panmictic species with a wide distribution range, provides a paradigmatic case. We compiled data published in the past 30 years on eel mortality during the continental phase of the life cycle for 15 eel stocks and calibrated a general model for mortality, considering the effects of body mass, temperature, stock density and gender. Estimated activation energy ( E  = 1.2 eV) was at the upper extreme reported for metabolic reactions. Estimated mortality rates (ranging between 0.02 year −1 at 8°C, low density and 0.47 year −1 at 18°C, high density for a body mass of 100 g) were appreciably lower than those of most fishes, most likely due to the exceptionally low energy-consuming metabolism of eel.
    Keywords: Anguilla anguilla ; Allometric theory ; Density-dependent survival ; Life history variation ; Temperature scaling of vital rates
    ISSN: 0029-8549
    E-ISSN: 1432-1939
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  • 4
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 2012, Vol.109(17), pp.6602-6607
    Description: Mathematical models can provide key insights into the course of an ongoing epidemic, potentially aiding real-time emergency management in allocating health care resources and by anticipating the impact of alternative interventions. We study the ex post reliability of predictions of the 2010–2011 Haiti cholera outbreak from four independent modeling studies that appeared almost simultaneously during the unfolding epidemic. We consider the impact of different approaches to the modeling of spatial spread of Vibrio cholerae and mechanisms of cholera transmission, accounting for the dynamics of susceptible and infected individuals within different local human communities. To explain resurgences of the epidemic, we go on to include waning immunity and a mechanism explicitly accounting for rainfall as a driver of enhanced disease transmission. The formal comparative analysis is carried out via the Akaike information criterion (AIC) to measure the added information provided by each process modeled, discounting for the added parameters. A generalized model for Haitian epidemic cholera and the related uncertainty is thus proposed and applied to the year-long dataset of reported cases now available. The model allows us to draw predictions on longer-term epidemic cholera in Haiti from multiseason Monte Carlo runs, carried out up to January 2014 by using suitable rainfall fields forecasts. Lessons learned and open issues are discussed and placed in perspective. We conclude that, despite differences in methods that can be tested through model-guided field validation, mathematical modeling of large-scale outbreaks emerges as an essential component of future cholera epidemic control. ; p. 6602-6607.
    Keywords: Data Collection ; Cholera ; Vibrio Cholerae ; Disease Transmission ; Health Services ; Immunity ; Mathematical Models ; Uncertainty ; Rain ; Human Communities
    ISSN: 0027-8424
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  • 5
    In: Global Change Biology, September 2015, Vol.21(9), pp.3323-3335
    Description: The global European eel () stock is critically endangered according to the , and the European Commission has urged the development of conservation plans aimed to ensure its viability. However, the complex life cycle of this panmictic species, which reproduces in the open ocean but spends most of its prereproductive life in continental waters (thus embracing a huge geographic range and a variety of habitat types), makes it difficult to assess the long‐term effectiveness of conservation measures. The interplay between local and global stressors raises intriguing cross‐scale conservation challenges that require a comprehensive modelling approach to be addressed. We developed a full life cycle model of the global European eel stock, encompassing both the oceanic and the continental phases of eel's life, and explicitly allowing for spatial heterogeneity in vital rates, availability of suitable habitat and settlement potential via a metapopulation approach. We calibrated the model against a long‐term time series of global European eel catches and used it to hindcast the dynamics of the stock in the past and project it over the 21st century under different management scenarios. Although our analysis relies on a number of inevitable simplifying assumptions and on data that may not embrace the whole range of variation in population dynamics at the small spatiotemporal scale, our hindcast is consistent with the general pattern of decline of the stock over recent decades. The results of our projections suggest that (i) habitat loss played a major role in the European eel decline; (ii) the viability of the global stock is at risk if appropriate protection measures are not implemented; (iii) the recovery of spawner escapement requires that fishing mortality is significantly reduced; and (iv) the recovery of recruitment might not be feasible if reproductive output is not enhanced.
    Keywords: Conservation ; European Eel ; Geographic Variation Of Vital Rates ; Habitat Loss ; Metapopulations ; Population Viability ; Reproductive Success ; Sustainable Fisheries Management
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 6
    In: Ecology Letters, April 2014, Vol.17(4), pp.426-434
    Description: River networks define ecological corridors characterised by unidirectional streamflow, which may impose downstream drift to aquatic organisms or affect their movement. Animals and plants manage to persist in riverine ecosystems, though, which in fact harbour high biological diversity. Here, we study metapopulation persistence in river networks analysing stage‐structured populations that exploit different dispersal pathways, both along‐stream and overland. Using stability analysis, we derive a novel criterion for metapopulation persistence in arbitrarily complex landscapes described as spatial networks. We show how dendritic geometry and overland dispersal can promote population persistence, and that their synergism provides an explanation of the so‐called `drift paradox’. We also study the geography of the initial spread of a species and place it in the context of biological invasions. Applications concerning the persistence of stream salamanders in the Shenandoah river, and the spread of two invasive species in the Mississippi‐Missouri are also discussed.
    Keywords: Bifurcations ; Dominant Eigenvalue ; Ecohydrology ; Extinction Debt ; Fluvial Systems ; Metapopulation Capacity ; Movement Ecology ; Topology
    ISSN: 1461-023X
    E-ISSN: 1461-0248
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  • 7
    In: Freshwater Biology, January 2018, Vol.63(1), pp.114-127
    Description: Proliferative kidney disease (PKD) is a high‐mortality pathology that critically affects freshwater salmonid populations. Infection is caused by the endoparasitic myxozoan Tetracapsuloides bryosalmonae, which exploits freshwater bryozoans as primary hosts. Incidence and severity of PKD have recently increased, largely owing to rising water temperatures linked to climate change, causing a decline in fish catches and local extinctions in many river systems. Here, building on a recently proposed local model of PKD transmission, a spatially explicit metacommunity framework is developed to study the spatial effects of the disease spread in idealised stream networks. At the local community scale, the model accounts for demographic and epidemiological dynamics of bryozoan and fish populations. At the network scale, the model couples the dynamics of each local community through hydrological transport of parasite spores and fish movement. The model also explicitly accounts for heterogeneity in habitat characteristics and hydrological conditions along a river network. Network effects are investigated by running simulation experiments on synthetic river network replicas derived from Optimal Channel Networks, spanning trees known to reproduce all the mutually connected topological and metric features of real rivers. Network connectivity can produce heterogeneous patterns of PKD prevalence even when the underlying spatial distributions of fish and bryozoans are homogeneous. Prevalence is generally higher at the downstream sites: if fish mobility is neglected, the spatial distribution of prevalence follows that of the upstream drainage area; otherwise, prevalence patterns are correlated with the proximity to the outlet. Downstream invasion speed of PKD is generally high, due to the fast dynamics of hydrological spore transport. For the tested values, effects of water temperature on prevalence heterogeneity are minor. However, climate change may increase invasion speed in both downstream and upstream directions. PKD can establish in bryozoan‐free river reaches, on the condition that the infection be sustained by upstream or downstream hot‐spots. These results further our understanding of the drivers of fish distribution in riverine ecosystems and may provide the basis for the development of intervention and management tools, especially facing climate change.
    Keywords: Climate Change ; Disease Ecology ; Epidemiological Model ; Fredericella Sultana ; Salmo Trutta
    ISSN: 0046-5070
    E-ISSN: 1365-2427
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  • 8
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 24 April 2012, Vol.109(17), pp.6602-7
    Description: Mathematical models can provide key insights into the course of an ongoing epidemic, potentially aiding real-time emergency management in allocating health care resources and by anticipating the impact of alternative interventions. We study the ex post reliability of predictions of the 2010-2011 Haiti cholera outbreak from four independent modeling studies that appeared almost simultaneously during the unfolding epidemic. We consider the impact of different approaches to the modeling of spatial spread of Vibrio cholerae and mechanisms of cholera transmission, accounting for the dynamics of susceptible and infected individuals within different local human communities. To explain resurgences of the epidemic, we go on to include waning immunity and a mechanism explicitly accounting for rainfall as a driver of enhanced disease transmission. The formal comparative analysis is carried out via the Akaike information criterion (AIC) to measure the added information provided by each process modeled, discounting for the added parameters. A generalized model for Haitian epidemic cholera and the related uncertainty is thus proposed and applied to the year-long dataset of reported cases now available. The model allows us to draw predictions on longer-term epidemic cholera in Haiti from multiseason Monte Carlo runs, carried out up to January 2014 by using suitable rainfall fields forecasts. Lessons learned and open issues are discussed and placed in perspective. We conclude that, despite differences in methods that can be tested through model-guided field validation, mathematical modeling of large-scale outbreaks emerges as an essential component of future cholera epidemic control.
    Keywords: Disease Outbreaks ; Rain ; Seasons ; Cholera -- Epidemiology
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 9
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 07 November 2017, Vol.114(45), pp.11992-11997
    Description: Proliferative kidney disease (PKD) is a major threat to wild and farmed salmonid populations because of its lethal effect at high water temperatures. Its causative agent, the myxozoan , has a complex lifecycle exploiting freshwater bryozoans as primary hosts and salmonids as secondary hosts. We carried out an integrated study of PKD in a prealpine Swiss river (the Wigger). During a 3-year period, data on fish abundance, disease prevalence, concentration of primary hosts' DNA in environmental samples [environmental DNA (eDNA)], hydrological variables, and water temperatures gathered at various locations within the catchment were integrated into a newly developed metacommunity model, which includes ecological and epidemiological dynamics of fish and bryozoans, connectivity effects, and hydrothermal drivers. Infection dynamics were captured well by the epidemiological model, especially with regard to the spatial prevalence patterns. PKD prevalence in the sampled sites for both young-of-the-year (YOY) and adult brown trout attained 100% at the end of summer, while seasonal population decay was higher in YOY than in adults. We introduce a method based on decay distance of eDNA signal predicting local species' density, accounting for variation in environmental drivers (such as morphology and geology). The model provides a whole-network overview of the disease prevalence. In this study, we show how spatial and environmental characteristics of river networks can be used to study epidemiology and disease dynamics of waterborne diseases.
    Keywords: Climate Change ; Edna ; Metacommunity Framework ; Parasite–Host Interactions ; Waterborne Epidemic ; Bryozoa -- Parasitology ; Fish Diseases -- Epidemiology ; Kidney Diseases -- Veterinary ; Myxozoa -- Pathogenicity ; Trout -- Parasitology
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 10
    Language: English
    In: Journal of Theoretical Biology, 14 June 2018, Vol.447, pp.126-138
    Description: Determining the conditions that favor pathogen establishment in a host community is key to disease control and eradication. However, focusing on long-term dynamics alone may lead to an underestimation of the threats imposed by outbreaks triggered by short-term transient phenomena. Achieving an effective epidemiological response thus requires to look at different timescales, each of which may be endowed with specific management objectives. In this work we aim to determine epidemicity thresholds for some prototypical examples of water-borne and water-related diseases, a diverse family of infections transmitted either directly through water infested with pathogens or by vectors whose lifecycles are closely associated with water. From a technical perspective, while conditions for endemicity are determined via stability analysis, epidemicity thresholds are defined through generalized reactivity analysis, a recently proposed method that allows the study of the short-term instability properties of ecological systems. Understanding the drivers of water-borne and water-related disease dynamics over timescales that may be relevant to epidemic and/or endemic transmission is a challenge of the utmost importance, as large portions of the developing world are still struggling with the burden imposed by these infections.
    Keywords: Generalized Reactivity ; Short- and Long-Term Instability ; Cholera ; Schistosomiasis ; Malaria ; Dengue Fever ; Disease Control ; Biology
    ISSN: 0022-5193
    E-ISSN: 1095-8541
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