Modeling Spatial Invasion of Ebola in West Africa

Abstract

The 2014-2015 Ebola Virus Disease (EVD) epidemic in West Africa was the largest ever recorded, representing a fundamental shift in Ebola epidemiology with unprecedented spatiotemporal complexity. We developed spatial transmission models using a gravity-model framework to explain spatiotemporal dynamics of EVD in West Africa at both the national and district-level scales, and to compare effectiveness of local interventions (e.g. local quarantine) and long-range interventions (e.g. border-closures). Incorporating spatial interactions, the gravity model successfully captures the multiple waves of epidemic growth observed in Guinea. Model simulations indicate that local-transmission reductions were most effective in Liberia, while long-range transmission was dominant in Sierra Leone. The model indicates the presence of spatial herd protection, wherein intervention in one region has a protective effect on surrounding regions. The district-level intervention analysis indicates the presence of intervention-amplifying regions, which provide above-expected levels of reduction in cases and deaths beyond their borders. The gravity-modeling approach accurately captured the spatial spread patterns of EVD at both country and district levels, and helps to identify the most effective locales for intervention. This model structure and intervention analysis provides information that can be used by public health policymakers to assist planning and response efforts for future epidemics.