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

Abstract

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

“…Our findings have direct implications on the design of effective disease control programs. In fact, the improved understanding of snail ecology implied by the prediction of their population abundances can directly refine spatially explicit disease transmission models by relaxing the key assumptions of stationary snail populations (32,33). By providing empirical and theoretical evidence for discriminating ecological processes across climatic zones and habitat types, our ecohydrological framework accounts for the relevant environmental drivers, especially the kinds of climatic seasonality and habitat ephemerality typical of the Sahelian ecotone.…”

“…This observation has nontrivial consequences on the determinants of snail abundance and denies the feasibility of all-purpose stationary and homogeneous reference population sizes being used in large-scale disease pattern identification. Formal methods (e.g., 37) are available to quantify the impact of seasonality in snail fluctuations on disease persistence and prevalence, which will extend directly existing, spatially explicit approaches to the geography of the disease (32,33). Population fluctuations in the perennial habitat of the south appeared to be in synchrony with snail abundance in the man-made reservoir located in the Sudano-Sahelian center of the country where early ecological studies took place (SI Appendix).…”

“…Extension and upscaling of our approach would be possible through the use of remotely sensed data on the hydrological drivers of snail abundance (SI Appendix), in the perspective of providing predictions of the effectiveness of control interventions. Our approach complements ecological range inference methods [e.g., maximum entropy modeling (40)], and transmission suitability indices incorporating snail biology (41) in assessing seasonal variations of snail abundance and their hydrological controls, yielding potential insight on the impacts of climate change on schistosomiasis transmission at regional scales (33,42).…”

“…(SI Appendix). This seasonality is in contrast to current assumptions of spatially explicit models of schistosomiasis transmission that neglect the dynamics of local snail abundance, which are typically assumed to be constant and treated as a parameter (32,33). Notably, the existing field studies focused on two sites in similar climatic zones and did not address quantitatively the underlying ecological processes driving population dynamics, particularly density effects and drivers borne out of external environmental forcings.…”

Climate-driven endemic cholera is modulated by human mobility in a megacity

“…Human mobility models have been extensively employed to infer mobility matrices (here Q ) in the framework of spatially-explicit models for the spread of waterborne diseases [19, 25, 20, 36]. Indeed, we are here interested in the spatial repartition of mobility, rather than mobility fluxes themselves (people per unit time).…”