Maximum clade credibility tree of complete envelope genes of DENV-1. Horizontal branches are drawn to a scale of estimated year of divergence. Coalescent times with 95% highest posterior density values (ranges in parentheses) and posterior probability values (all 1.0) of key nodes are shown. DENV-1 outbreaks are indicated at the end of branches according to the outbreak-causing clades. The consensus E amino acid sequences of Malaysian DENV-1 isolates used were indicated as Ia, Ib, Ic, IIa, IIb, IIIa and IIIb. The DENV-1 isolates from Malaysia are highlighted in grey. Viruses marked with * are the rare isolates. A total of 39 new Malaysian DENV-1 E gene sequences were used [EMBL:FN825674, EMBL:FR666920-FR666928].