Evolutionary relationships of E gene sequences of DENV-1 (1478 nt). Maximum-Likelihood original trees derived from 110 DENV-1 E gene sequences (90 PICTs and 20 retrieved from GenBank). The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) is shown for values over 80. The period (years) these strains have been collected is indicated just after the country isocode. The number in brackets represents the number of NC DENV-1 strains identical (nucleotide sequence) to the strain reported on the tree. The 73 (53 + 20 in brackets) NC DENV-1 strains are shown in bold. Genbank accession numbers of the DENV-1 E gene sequenced for this study are reported in Additional file1.