Fluid spatial dynamics of West Nile virus in the USA: Rapid spread in a permissive host environment

Journal of Virology
By: , and 



The introduction of West Nile virus (WNV) into North America in 1999 is a classical example of viral emergence in a new environment, with its subsequent dispersion across the continent having a major impact on local bird populations. Despite the importance of this epizootic, the pattern, dynamics and determinants of WNV spread in its natural hosts remain uncertain. In particular, it is unclear whether the virus encountered major barriers to transmission, or spread in an unconstrained manner, and if specific viral lineages were favored over others indicative of intrinsic differences in fitness. To address these key questions in WNV evolution and ecology we sequenced the complete genomes of approximately 300 avian isolates sampled across the USA between 2001-2012. Phylogenetic analysis revealed a relatively ‘star-like' tree structure, indicative of explosive viral spread in US, although with some replacement of viral genotypes through time. These data are striking in that viral sequences exhibit relatively limited clustering according to geographic region, particularly for those viruses sampled from birds, and no strong phylogenetic association with well sampled avian species. The genome sequence data analysed here also contain relatively little evidence for adaptive evolution, particularly on structural proteins, suggesting that most viral lineages are of similar fitness, and that WNV is well adapted to the ecology of mosquito vectors and diverse avian hosts in the USA. In sum, the molecular evolution of WNV in North America depicts a largely unfettered expansion within a permissive host and geographic population with little evidence of major adaptive barriers.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Fluid spatial dynamics of West Nile virus in the USA: Rapid spread in a permissive host environment
Series title Journal of Virology
DOI 10.1128/JVI.02305-15
Volume 90
Issue 2
Year Published 2016
Language English
Publisher American Society for Microbiology
Publisher location Baltimore, MD
Contributing office(s) National Wildlife Health Center
Description 11 p.
First page 862
Last page 872
Country United States
Online Only (Y/N) N
Additional Online Files (Y/N) N
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