Cell
Volume 161, Issue 7, 18 June 2015, Pages 1516-1526
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Article
Ebola Virus Epidemiology, Transmission, and Evolution during Seven Months in Sierra Leone

https://doi.org/10.1016/j.cell.2015.06.007Get rights and content
Under a Creative Commons license
open access

Highlights

  • In Sierra Leone, transmission has primarily been within-country, not between-country

  • Infectious doses are large enough for intrahost variants to transmit between hosts

  • A prolonged epidemic removes deleterious mutations from the viral population

  • There is preliminary evidence for human RNA editing effects on the Ebola genome

Summary

The 2013–2015 Ebola virus disease (EVD) epidemic is caused by the Makona variant of Ebola virus (EBOV). Early in the epidemic, genome sequencing provided insights into virus evolution and transmission and offered important information for outbreak response. Here, we analyze sequences from 232 patients sampled over 7 months in Sierra Leone, along with 86 previously released genomes from earlier in the epidemic. We confirm sustained human-to-human transmission within Sierra Leone and find no evidence for import or export of EBOV across national borders after its initial introduction. Using high-depth replicate sequencing, we observe both host-to-host transmission and recurrent emergence of intrahost genetic variants. We trace the increasing impact of purifying selection in suppressing the accumulation of nonsynonymous mutations over time. Finally, we note changes in the mucin-like domain of EBOV glycoprotein that merit further investigation. These findings clarify the movement of EBOV within the region and describe viral evolution during prolonged human-to-human transmission.

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This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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Co-first author

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Co-senior author