Identifying spatiotemporal dynamics of Ebola in Sierra Leone using virus genomes

April 25, 2017


Containing the recent West African outbreak of Ebola virus (EBOV) required the deployment of substantial global resources. Operationally, health workers and surveillance teams treated cases, collected genetic samples, and tracked case contacts. Despite the substantial progress in analyzing and modeling EBOV epidemiological data, a complete characterization of the spatiotemporal spread of Ebola cases remains a challenge. In this work, we offer a novel perspective on the EBOV epidemic that utilizes virus genome sequences to inform population-level, spatial models. Calibrated to phylogenetic linkages, these dynamic spatial models provide unique insight into the disease mobility of EBOV in Sierra Leone. Further, we developed a model selection framework that identifies important epidemiological variables influencing the spatiotemporal propagation of EBOV. Consistent with other investigations, our results show that the spread of EBOV during the beginning and middle portions of the epidemic strongly depended on the size of and distance between populations. Our analysis also revealed a substantial decline in the dependence on population size at the end of the epidemic, coinciding with the large-scale intervention campaign: Operation Western Area Surge. More generally, we believe this framework, pairing molecular diagnostics with dynamic models, has the potential to be a powerful forecasting tool along with offering operationally-relevant guidance for surveillance and sampling strategies during an epidemic.

Fig 1 Virus genome data from EBOV cases in Sierra Leone characterizes the spatial spread of the epidemic. (A) The time course is shown for the number of confirmed cases24 and sequenced EBOV genomes22. Three stages of the epidemic are highlighted. (B) Genetic linkages are illustrated with ancestors (open circles) and descendants (closed dots), both colored by the origin district shown in map key. The blue arrow highlights a linkage from the W. Urban to Kenema districts. (C) Chiefdom populations (grayscale) and major roads (yellow traces) are illustrated on the map of Sierra Leone. The blue arrow highlights the fastest driving route between the W. Urban to Kenema district.