FIG. 3.

Phylogenetic study of the gp90 nucleotide sequences of longitudinal viral isolates from progressor ponies 564 and 567. Phylogenetic trees were constructed with the neighbor joining method using V2 to V8 nucleotide sequences derived from plasma taken during fever I (■), fever II (⧫), fever III (●), fever IV (▾), fever V (▴), and fever VI (✦) and from MDM cultures obtained during asymptomatic stage at 800 dpi (⋆). Bootstrap values were determined over 1,000 iterations and are indicated at the nodes of the branches. Branch lengths are proportional to the distance existing between the sequences.