Genotype-specific variation in West Nile virus dispersal in California

Nisha K Duggal,William K Reisen,Ying Fang,Ruchi M Newman,Xiao Yang,Gregory D Ebel,Aaron C Brault

doi:10.1016/j.virol.2015.07.004

Abstract

West Nile virus (WNV) is an arbovirus that was first reported in North America in New York in 1999 and, by 2003, had spread more than 4000km to California. However, variation in viral genetics associated with spread is not well understood. Herein, we report sequences for more than 100 WNV isolates made from mosquito pools that were collected from 2003 to 2011 as part of routine surveillance by the California Mosquito-borne Virus Surveillance System. We performed phylogeographic analyses and demonstrated that 5 independent introductions of WNV (1 WN02 genotype strain and 4 SW03 genotype strains) occurred in California. The SW03 genotype of WNV was constrained to the southwestern U.S. and had a more rapid rate of spread. In addition, geographic constraint of WNV strains within a single region for up to 6 years suggest viral maintenance has been driven by resident, rather than migratory, birds and overwintering in mosquitoes.

Highlights

West Nile virus (WNV) is an arbovirus of the family Flaviviridae that was first identified in North America in 1999
Full-length WNV genomes were successfully assembled from 112 mosquito pools from 10 mosquito control districts in California: Sacramento-Yolo (SAYO), Shasta (SHAS), Coachella Valley (COAV), Greater Los Angeles County (GRLA), Sutter-Yuba (SUYA), Kern (KERN), Contra Costa (CNTR), Imperial County (IMPR), Owens Valley (INYO), and San Bernardino (SANB)
Most isolates were collected in 5 mosquito control districts: GRLA, KERN, COAV, SAYO, and CNTR (Fig. 2A), which together accounted for the locations of 50% of human WNV disease cases in CA

Summary

Introduction

West Nile virus (WNV) is an arbovirus of the family Flaviviridae that was first identified in North America in 1999. In the U.S, Culex mosquitoes are the primary vectors for WNV [1,2,3,4], and passerine birds are the most common avian host [1, 5]. Humans, equines, other mammals, and many bird species do not contribute to the enzootic cycle or evolution of WNV. WNV was first reported in New York and reached the West Coast within 4 years. Three autochthonous human cases of WNV in southern California were reported to ArboNET in 2003. Human WNV disease cases in northern and southern California were reported to ArboNET the following year, and, by the conclusion of the 2004 transmission season, WNV had been detected in every county in the state of California [7]

Methods

Results

Conclusion