The complete genome structure and phylogenetic relationship of infectious hematopoietic necrosis virus

Infectious hematopoietic necrosis virus (IHNV), a member of the family Rhabdoviridae, causes a severe disease with high mortality in salmonid fish. The nucleotide sequence (11,131 bases) of the entire genome was determined for the pathogenic WRAC strain of IHNV from southern Idaho. This allowed detailed analysis of all 6 genes, the deduced amino acid sequences of their encoded proteins, and important control motifs including leader, trailer and gene junction regions. Sequence analysis revealed that the 6 virus genes are located along the genome in the 3' to 5' order: nucleocapsid (N), polymerase-associated phosphoprotein (P or M1), matrix protein (M or M2), surface glycoprotein (G), a unique non-virion protein (NV) and virus polymerase (L). The IHNV genome RNA was found to have highly complementary termini (15 of 16 nucleotides). The gene junction regions display the highly conserved sequence UCURUC(U)7RCCGUG(N)4CACR (in the vRNA sense), which includes the typical rhabdovirus transcription termination/polyadenylation signal and a novel putative transcription initiation signal. Phylogenetic analysis of M, G and L protein sequences allowed insights into the evolutionary and taxonomic relationship of rhabdoviruses of fish relative to those of insects or mammals, and a broader sense of the relationship of non-segmented negative-strand RNA viruses. Based on these data, a new genus, piscivirus, is proposed which will initially contain IHNV, viral hemorrhagic septicemia virus and Hirame rhabdovirus.