Theophile Mande

A Theoretical Analysis of the Geography of Schistosomiasis in Burkina Faso Highlights the Roles of Human Mobility and Water Resources Development in Disease Transmission.

We study the geography of schistosomiasis across Burkina Faso by means of a spatially explicit model of water-based disease dynamics. The model quantitatively addresses the geographic stratification of disease burden in a novel framework by explicitly accounting for drivers and controls of the disease, including spatial information on the distributions of population and infrastructure, jointly with a general description of human mobility and climatic/ecological drivers. Spatial patterns of disease are analysed by the extraction and the mapping of suitable eigenvectors of the Jacobian matrix subsuming the stability of the disease-free equilibrium. The relevance of the work lies in the novel mapping of disease burden, a byproduct of the parametrization induced by regional upscaling, by model-guided field validations and in the predictive scenarios allowed by exploiting the range of possible parameters and processes. Human mobility is found to be a primary control at regional scales both for pathogen invasion success and the overall distribution of disease burden. The effects of water resources development highlighted by systematic reviews are accounted for by the average distances of human settlements from water bodies that are habitats for the parasite’s intermediate host. Our results confirm the empirical findings about the role of water resources development on disease spread into regions previously nearly disease-free also by inspection of empirical prevalence patterns. We conclude that while the model still needs refinements based on field and epidemiological evidence, the proposed framework provides a powerful tool for large-scale public health planning and schistosomiasis management.

Hydrology and density feedbacks control the ecology of intermediate hosts of schistosomiasis across habitats in seasonal climates

Significance Some freshwater snail species are intermediate hosts in the life cycle of parasites causing human schistosomiasis, a neglected water-based disease (treatable but debilitating and poverty-reinforcing) affecting about 150 million people yearly in sub-Saharan Africa alone. Snail abundance is thus often the target of epidemiological control measures of schistosomiasis incidence. Our work studies the ecology of host snails through field campaigns and theoretical models within natural/artificial water habitats across Burkina Faso’s highly seasonal climatic zones. Snail abundance is shown to depend on hydrological controls and to obey density-dependent demographic evolution. Statistical methods based on model averaging yield reliable snail abundance projections. Quantitative predictions on epidemiological effects of water resources development, risk mapping, and the allocation of control measures appear within reach. 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.

Suppressed convective rainfall by agricultural expansion in southeastern Burkina Faso

With the green economy being promoted as a path to sustainable development and food security within the African continent, the influx of agricultural land is proliferating at a rapid pace often replacing natural savannah forests. Where agriculture is primarily rainfed, the possible adverse impacts of agricultural land influx on rainfall occurrences in water-limited areas such as West Africa warrant attention. Using field observations complemented by model calculations in southeastern Burkina Faso, the main causes of a 10-30% suppressed daytime rainfall recorded over agricultural fields when referenced to natural savannah forests are examined. Measurements and model runs reveal that the crossing of the mixed layer height and lifting condensation levels, a necessary condition for cloud formation and subsequent rainfall occurrence, was 30% more frequent above the natural savannah forest. This increase in crossing statistics was primarily explained by increases in measured sensible heat flux above the savannah forest rather than differences in lifting condensation heights.

Toward a New Approach for Hydrological Modeling: A Tool for Sustainable Development in a Savanna Agro-System

Agriculture in Tambarga, a small, remote village in the landlocked country of Burkina Faso, is dependent on the seasonally variable local hydrology. Extreme seasonal and spatial variability of rainfall significantly impacts the livelihood of farmers, who depend mainly on rainfed agriculture. This dependence on rainfed production makes them particularly vulnerable to meteorological conditions, and they continually experience food insecurity. The groundwater is promising as storage to mitigate effects of drought. However, because of its interaction with the various hydrological components, we need to better understand all the processes to fully assess the impacts of possible solutions. Hydrological and meteorological data were collected over a two-and-a-half-year period in the catchment adjacent to the village (area = 3.5 km²) to address these issues. The field studies show that the major portion of storm runoff was generated in the upper savanna basin, while baseflow appears to be mostly originating from the downstream agricultural field. The seasonal cycle of groundwater appears to control the stream flow and therefore, the continuous flow over the entire stream occurred when the water tables became interconnected and surfaced the ground level. Additionally, this paper discusses water management scenarios (open dam, deeper wells and buried dam) for agricultural purposes using a simple and comprehensive hydrological model. Simulations based on reducing evaporation rate by keeping the water underground present a solution that could improve agricultural production, and therefore, reduce vulnerability of Tambarga’s farmers to climate change.