Figure 4. Maximum parsimony phylogenetic tree derived from complete genomic sequences showing relationships of the newly isolated Venezuelan equine encephalitis virus (VEEV) strain (MX01-22) to other strains from Mexico and Guatemala. Numbers indicate nucleotide substitutions assigned to each branch. All nodes had bootstrap values of 100%, except the OAX131-37820 (62%) and GU68-GU80 (<50%) groupings. Relative rates tests applied to the branches indicated a rate of nucleotide substitution in Mexico of 2.0–2.9 x 10–4 subst/nt/y since 1993, and 6.8 x 10–5 for the Guatemalan lineage from 1968–1980. These data suggest continuous circulation of VEEV in Mexico since 1993.