Introductions of West Nile virus strains to Mexico

Abstract

Complete genome sequencing of 22 West Nile virus isolates suggested 2 independent introductions into Mexico. A previously identified mouse-attenuated glycosylation variant was introduced into southern Mexico through the southeastern United States, while a common US genotype appears to have been introduced incrementally into northern Mexico through the southwestern United States.

Figure 1

Map showing hypothetical routes of West Nile virus introduction into Mexico. Circles indicate locations of isolates in the Florida-Louisiana-Tabasco 2001–2003 clade (Figure 2). Stars indicate locations of isolates in the California-Arizona-northern Mexico clade.

Figure 2

Phylogenetic tree generated from the complete open reading frame of West Nile virus sequences using a Bayesian analysis. Virus strains are labeled by GenBank accession number followed by the state and/or country, year, and host of isolation. Numbers indicate Bayesian probability values followed by neighbor-joining bootstrap values for groups to the right. The tree was rooted by using an outgroup comprised of Old World strains of West Nile virus, including a lineage 2 strain (Table).