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“Frozen evolution” of an RNA virus suggests accidental release as a potential cause of arbovirus re-emergence


David J. Pascall

Kyriaki Nomikou


Stephan Zientara

Ana da Silva Filipe

Bernd Hoffmann

Maude Jacquot

Joshua B. Singer

Kris de Clercq


Corinne Sailleau

Cyril Viarouge

Carrie Batten

Giantonella Puggioni

Ciriaco Ligios

Giovanni Savini

Piet A. van Rijn

Roman Biek

Massimo Palmarini


Andrew Fraser Read


© 2020 Pascall et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The mechanisms underlying virus emergence are rarely well understood, making the appearance of outbreaks largely unpredictable. Bluetongue virus serotype 8 (BTV-8), an arthropod-borne virus of ruminants, emerged in livestock in northern Europe in 2006, spreading to most European countries by 2009 and causing losses of billions of euros. Although the outbreak was successfully controlled through vaccination by early 2010, puzzlingly, a closely related BTV-8 strain re-emerged in France in 2015, triggering a second outbreak that is still ongoing. The origin of this virus and the mechanisms underlying its re-emergence are unknown. Here, we performed phylogenetic analyses of 164 whole BTV-8 genomes sampled throughout the two outbreaks. We demonstrate consistent clock-like virus evolution during both epizootics but found negligible evolutionary change between them. We estimate that the ancestor of the second outbreak dates from the height of the first outbreak in 2008. This implies that the virus had not been replicating for multiple years prior to its re-emergence in 2015. Given the absence of any known natural mechanism that could explain BTV-8 persistence over this long period without replication, we hypothesise that the second outbreak could have been initiated by accidental exposure of livestock to frozen material contaminated with virus from approximately 2008. Our work highlights new targets for pathogen surveillance programmes in livestock and illustrates the power of genomic epidemiology to identify pathways of infectious disease emergence.


Pascall, D. J., Nomikou, K., Bréard, E., Zientara, S., da Silva Filipe, A., Hoffmann, B., …Palmarini, M. (2020). “Frozen evolution” of an RNA virus suggests accidental release as a potential cause of arbovirus re-emergence. PLoS Biology, 18(4), Article e300067.

Journal Article Type Article
Acceptance Date Mar 24, 2020
Online Publication Date Apr 28, 2020
Publication Date Apr 28, 2020
Deposit Date May 6, 2020
Publicly Available Date May 6, 2020
Journal PLoS Biology
Print ISSN 1544-9173
Electronic ISSN 1545-7885
Publisher Public Library of Science
Peer Reviewed Peer Reviewed
Volume 18
Issue 4
Article Number e300067
Public URL
Publisher URL
Additional Information Pascall DJ, Nomikou K, Bréard E, Zientara S, Filipe AdS, Hoffmann B, et al. (2020) “Frozen evolution” of an RNA virus suggests accidental release as a potential cause of arbovirus re-emergence. PLoS Biol 18(4): e3000673.


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