Abstract
Enzootic strains of Venezuelan equine encephalitis virus (VEEV) have been isolated from febrile patients in the Peruvian Amazon Basin at low but consistent levels since the early 1990s. Through a clinic-based febrile surveillance program, we detected an outbreak of VEEV infections in Iquitos, Peru, in the first half of 2006. The majority of these patients resided within urban areas of Iquitos, with no report of recent travel outside the city. To characterize the risk factors for VEEV infection within the city, an antibody prevalence study was carried out in a geographically stratified sample of urban areas of Iquitos. Additionally, entomological surveys were conducted to determine if previously incriminated vectors of enzootic VEEV were present within the city. We found that greater than 23% of Iquitos residents carried neutralizing antibodies against VEEV, with significant associations between increased antibody prevalence and age, occupation, mosquito net use, and overnight travel. Furthermore, potential vector mosquitoes were widely distributed across the city. Our results suggest that while VEEV infection is more common in rural areas, transmission also occurs within urban areas of Iquitos, and that further studies are warranted to identify the precise vectors and reservoirs involved in urban VEEV transmission.
Highlights
Members of the Venezuelan equine encephalitis virus (VEEV) complex are arboviruses belonging to the Alphavirus genus of the Togaviridae family
In Iquitos, Peru, a city of 350,000 situated in the Amazon forest, we normally observe 10–14 VEE cases per year associated with people traveling to rural areas where strains VEE virus circulate among forest mosquitoes and rodents
Evidence for VEE Outbreak From 2000–2004 the Naval Medical Research Center Detachment (NMRCD) febrile surveillance program detected up to four VEEV cases per month with annual totals ranging from 10–14 cases (Table 1)
Summary
Members of the Venezuelan equine encephalitis virus (VEEV) complex are arboviruses belonging to the Alphavirus genus of the Togaviridae family. Two transmission cycles have been identified: an enzootic cycle, maintained among rodent reservoirs in forest habitats, and an epizootic cycle that causes high rates of mortality in horses as well as epidemics among human populations [4] These cycles are typically associated with distinct subtypes of the VEE virus complex: subtypes IAB and IC with equine epizootics, subtypes ID, IF, and II–VI with the equine avirulent enzootic cycle [4,6], and subtype IE with both enzootic and equine-virulent transmission cycles [7,8,9]. Strains of the enzootic subtype ID (Columbia/Venezuela genotype) show less than 0.5% divergence from epizootic IAB and IC subtypes at the amino acid level [10,11,12] Based on this genetic conservation, epizootic strains have been proposed to emerge periodically from progenitor strains continuously maintained in an enzootic forest cycle. A single amino acid change within the E2 envelope gene has been shown to confer an epizootic phenotype on an enzootic VEEV strain [10,11,12,13]
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