Venezuelan equine encephalitis in Panama: fatal endemic disease and genetic diversity of etiologic viral strains

Abstract

Venezuelan equine encephalitis (VEE) is a reemerging, mosquito-borne viral disease of the neotropics that is severely debilitating and sometimes fatal to humans. Periodic epidemics mediated by equine amplification have been recognized since the 1920s, but interepidemic disease is rarely recognized. We report here clinical findings and genetic characterization of 42 cases of endemic VEE detected in Panama from 1961-2004. Recent clusters of cases occurred in Darien (eastern Panama) and Panama provinces (central Panama) near rainforest and swamp habitats. Patients ranged from 10 months to 48 years of age, and the more severe cases with neurological complications, including one fatal infection, were observed in children. The VEE virus strains isolated from these cases all belonged to an enzootic, subtype ID lineage known to circulate among sylvatic vectors and rodent reservoir hosts in Panama and Peru. These findings underscore endemic VEE as an important but usually neglected arboviral disease of Latin America.

Figure 1. Map of Panama showing the locations of the Venezuelan equine encephalitis cases.

Figure 2. Phylogenetic tree generated from partial PE2 gene sequences of Panamanian VEEV strains and homologous VEE complex alphavirus sequences from the GenBank library.

The tree was produced using the neighbor joining program implemented in PAUP 4.0 . VEEV strains are denoted by abbreviated country and year of isolation, followed by strain designation. Panamanian strains include abbreviated province in parentheses as follows: BT – Bocas del Toro; COC – Cocle; COL – Colon; DA – Darien; PA – Panama; VE – Veraguas. Numbers indicate bootstrap values for clades.