Maximum-likelihood phylogenetic tree of the 1,480-nt envelope gene region from Western hemisphereDENV-1 isolates. Sequences are labeled with GenBank accession numbers, country, and year. Countries are given as standard 3-letter codes. Scale bar indicates number of substitutions per site. The Martin County and Key West sequences are shown in red; Central American sequences, in blue; Caribbean sequences, in green; South American sequences, in purple, Asian/Pacific sequences, in black. Isolates from Hawaii (USA) and Easter Island (CHI) are of Asian origin and form an out group. Viruses group by geography and by year. The bootstrap values of the important nodes separating Central American from South American and recent Caribbean strains are shown. The tree was drawn by using FigTree software (http://tree.bio.ed.ac.uk/software/figtree).