FIG. 3.

Phylogenetic tree of 615-bp long nucleic acid sequences within the G gene (corresponding to nucleotide positions 3446 to 4061 of the reference strain [GenBank accession no. X89213]) (42) of 19 IHNVs from naturally infected salmonid fish from Austria, one IHNV from Italy, two IHNV reference strains from the United States and from France investigated in the present study, as well as 45 previously published IHNV sequences, mainly from the United States, Germany, and Japan. Analyses were performed by using the PHYLIP phylogeny program (version 3,57c package). The tree was rooted with the five Japanese (JRt) sequences. Bootstrap values are shown on the nodes of the clades that they are supporting. The IHNV strains used for vaccine development are indicated in dark red. The indicated years are the years in which the strains were isolated; if marked “n.d.,” these data were not available. Abbreviations: t.p., this paper; unpubl., unpublished. The phylogenetic tree demonstrates three major groups: M, U+L, and JRt. European isolates cluster only within the M group and form two genetic subgroups: M-Eur1 and M-Eur2. Austrian isolates cluster within both European subgroups (in the M-Eur1 subgroup [indicated in blue] and in the M-Eur2 subgroup [indicated in green]). The M-Eur2 subgroup comprises more recent isolates indicative of a genetic shift toward the M-Eur2 subgroup since the late 1990s.