Chikungunya virus dispersal and evolution. Phylogenetic trees were produced using alignments of complete or nearly-complete Chikungunya virus nucleotide sequences, from which the E1 226 codon was removed. Bootstrap resampling values are indicated at the main branches. Strains with the A226V mutation are indicated. In the tree on the right, horizontal bars are proportional to genetic distances. The tree on the left shows only the topology of the reconstruction. Branches supported by a bootstrap <60 are collapsed. Colours that identify the different lineages are the same as in figure 2. Central African strains that have been assigned to a given lineage based only on partial sequencing of the E1 gene are indicated in the exploded yellow bubble (a phylogenetic branch reconstructed from E1 sequences is shown). Isolates in the East-South-Africa, Asia and West-Africa lineages, which have been characterised only in the E1 gene are indicated.