"Mid-G" region sequences of the glycoprotein gene of Austrian infectious hematopoietic necrosis virus isolates form two lineages within European isolates and are distinct from American and Asian lineages

Abstract

Infectious hematopoietic necrosis virus (IHNV) is one of the most important pathogens of salmonid fish. In this study a comprehensive phylogenetic analysis of the genetic evolution and variety of Austrian IHNV strains, as well as selected strains ensuring worldwide coverage, is presented. The phylogenetic investigation is based on sequences comprising the "mid-G" region of the G gene, and it includes all currently available IHNV sequences of the G gene with a length of at least 615 bp. Austrian IHNVs are located--together with other European IHNV isolates--in two clusters of genogroup M (M-Eur1 and M-Eur2) and are clearly separated from American and Asian lineages. The genetic clustering, however, could not be linked to certain clinical symptoms or significant differences in the mortality rates.

FIG. 1.

Examples of clinical signs observed in IHNV-infected rainbow trout.

FIG. 2.

IHNV immunofluorescence pattern in EPC cells.

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 Abbreviations: t.p., this paper; unpubl., unpublished.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.