Molecular epidemiology of eastern equine encephalitis virus, New York

Abstract

Perpetuation, overwintering, and extinction of eastern equine encephalitis virus (EEEV) in northern foci are poorly understood. We therefore sought to describe the molecular epidemiology of EEEV in New York State during current and past epizootics. To determine whether EEEV overwinters, is periodically reintroduced, or both, we sequenced the E2 and partial NSP3 coding regions of 42 EEEV isolates from New York State and the Eastern Seaboard of the United States. Our phylogenetic analyses indicated that derived subclades tended to contain southern strains that had been isolated before genetically similar northern strains, suggesting southern to northern migration of EEEV along the Eastern Seaboard. Strong clustering among strains isolated during epizootics in New York from 2003-2005, as well as from 1974-1975, demonstrates that EEEV has overwintered in this focus. This study provides molecular evidence for the introduction of southern EEEV strains to New York, followed by local amplification, perpetuation, and overwintering.

Figure 1

A) United States map showing locations of eastern equine encephalitis virus strains sequenced in this study. New York State (NY) highlighted in blue; New Jersey (NJ), Virginia (VA), Florida (FL), Louisiana (LA) highlighted in gray. Map courtesy of www.theodora.com/maps, used with permission. B) New York counties where eastern equine encephalitis virus (EEEV) strains have been located (shaded). Dotted box indicates focus of most EEEV activity.

Figure 2

Maximum-likelihood phylogenetic tree of eastern equine encephalitis virus strains, based on the complete E2 coding sequence. Numbers at the nodes indicate bootstrap confidence estimated by 1,000 neighbor-joining replicates on the maximum-likelihood tree. The tree was rooted with lineage II (Brazil56), III (Panama86), and IV (Brazil85) strains.

Figure 4

Phylogenetic tree of NSP3 coding region of subset of lineage I eastern equine encephalitis virus strains, unrooted neighbor-joining analysis.

Figure 3

Phylogenetic tree of subset of lineage I eastern equine encephalitis virus strains, unrooted neighbor-joining analysis of E2 coding region. Strains included are identical to those used in the NSP3 coding region analysis.