EpidemicsA big-picture look at the world’s worst Ebola epidemic: West Africa, 2013-2016

An international effort to analyze the entire database of Ebola virus genomes from the 2013–2016 West African epidemic reveals insights into factors that sped or slowed the rampage and calls for using real-time sequencing and data-sharing to contain future viral disease outbreaks.

Published in the journal Nature, the analysis found that the epidemic unfolded in small, overlapping outbreaks with surprisingly few infected travelers sparking new outbreaks elsewhere, each case representing a missed opportunity to break the transmission chain and end the epidemic sooner.

“We calculated that 3.6 percent of cases traveled, basically meaning that if you were able to focus on those mobile cases and reduce their mobility, you might have had a disproportionate effect on the epidemic,” said computational biologist Dr. Gytis Dudas, a Mahan Postdoctoral Fellow at Fred Hutchinson Cancer Research Center and the paper’s lead author.

Fred Hutch notes that the West African Ebola epidemic dwarfed all previous central African outbreaks of the virus, sickening more than 28,000 people and killing more than 11,000 of them.

The 1,610 Ebola virus genomes analyzed by the researchers represented more than 5 percent of the known cases, the largest sample analyzed for a single human epidemic. The analysis is the first to look at how Ebola spread, proliferated and declined across all three countries most affected: Guinea, Sierra Leone and Liberia. Previous analyses focused primarily on either a single country, a limited time frame or used fewer sequences.

The new paper also amounts to a manifesto for collaborative science, with 96 scientists from 60 institutions in 18 countries listed as authors. Many of them had worked on earlier papers as clinicians gathering blood samples, researchers doing genome sequencing or analysts drawing on portions of the dataset. Dudas and senior author Dr. Andrew Rambaut of the Institute of Evolutionary Biology at Scotland’s University of Edinburgh were involved in the analyses for many of these efforts. 

The authors’ intention, they wrote, was for this comprehensive analysis to “provide a framework for predicting the behavior of future outbreaks for Ebola virus” and other human pathogens and to guide targeted, life-saving responses. 

Cities aided virus’ spread, distance slowed it
The new analysis assessed twenty-five factors that could have contributed to the spread and duration of the West African epidemic. It confirmed the common perception that cities played a major role in the magnitude of the epidemic compared to central African outbreaks that had occurred in remote, sparsely populated regions.

Distance