Figure 1. Map of study sites in Ecuador, Peru, and Venezuela. The study in Peru and Ecuador was operated jointly by the US Naval Medical Research Center Detachment with each country’s Institutes of Health. Samples from Venezuela were collected in and around Maracay through the Aragua State Epidemiologic Surveillance Program from patients with suspected dengue virus (DENV) infection. Cities denoted by filled circles indicate study sites where DENV serotype 4 strains were isolated, whereas open circles denote active study sites where no DENV–4 circulation was detected during the course of the study.