Links between infrastructure for human movement and early Ebola outbreak trajectories

Human movement drives the transmission and spread of communicable pathogens. It is particularly important for emerging pathogens when population susceptibility is high and spillover events are rare, which is often the case for Ebola virus (EBOV) in humans. From the first documentation in 1976 to 2020, 18 EBOV outbreaks have occurred in humans, all in Central and West Africa. Many were relatively small and spatially contained; two large outbreaks that spread widely began in 2013 and 2018. To assess the relationship between human movement and Ebola cases, we used transportation infrastructure as a proxy for movement. We also assessed cases in the first 100 days of each outbreak because this is a time point of significance in outbreak response assessment and has recently also become a goal for developing novel solutions for emerging pathogens. We digitized a printed map series and measured contemporaneous road and river networks surrounding spillover sites. We found that the lengths of roads and rivers near spillover sites at the time of spillovers were significantly correlated with the number of Ebola cases in the first 100 days of each outbreak. This relationship was consistent across time and space and suggests that static measures of transportation networks during an outbreak are reasonable indicators of connectivity, movement, and potential pathogen spread. This finding may be useful for guiding management and early containment efforts for outbreaks in data-limited settings to understand connectivity and movement from source locations.