Maximum likelihood tree (PhyML) of the (a) S1 and (b) M2 segment of PRV-3. Isolates are marked as following: Red, Danish isolates associated with disease; blue, Danish isolates from 1995; yellow, German isolates; green, Chilean isolates; light blue, Italian isolates; grey, Norwegian isolates; purple, Scottish isolates; #, brown trout; X, coho salmon; Y, Atlantic salmon; bold, sequence isolates that change position. Isolates originating from the same farm sampled at the same or different time points are marked with (A), (B), (C), (D), (E), and (F). Subtyping of PRV-3a and -3b is based on the S1 segment only. The PRV-3a clade consists of Norwegian isolates only, while the PRV-3b clade consists of isolates from Europe and Chile.