Virology. 2015 Nov;485:79-85. doi: 10.1016/j.virol.2015.07.004. Epub 2015 Jul 25.

Genotype-specific variation in West Nile virus dispersal in California.

Duggal NK¹, Reisen WK², Fang Y², Newman RM³, Yang X³, Ebel GD⁴, Brault AC⁵.

Author information

¹Division of Vector-borne Diseases, Centers for Disease Control and Prevention, Fort Collins, CO, USA.
²Center for Vectorborne Diseases, University of California, Davis, CA, USA.
³Broad Institute of Harvard and Massachusetts Institute of Technology, Cambridge, MA, USA.
⁴Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO, USA.
⁵Division of Vector-borne Diseases, Centers for Disease Control and Prevention, Fort Collins, CO, USA. Electronic address: abrault@cdc.gov.

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 4000 km 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.