title: Virulence of viral haemorrhagic septicaemia virus (VHSV) genotype III in rainbow trout.
abstract: In general, viral haemorrhagic septicaemia virus (VHSV) isolates from marine fish species in European waters (genotypes GIb, GII and GIII) are non- to low virulent in rainbow trout. However, a VHSV isolation was made in 2007 from a disease outbreak in sea farmed rainbow trout in Norway. The isolate, named NO-2007-50-385, was demonstrated to belong to GIII. This isolate has attracted attention to assess which of the viral genome/proteins might be associated with the virulence in rainbow trout. In this study, we describe the difference of virulence in rainbow trout between the NO-2007-50-385 and 4p168 isolates as representatives of virulent and non-virulent GIII isolates, respectively. Rainbow trout were bath challenged with VHSV NO-2007-50-385 for 1 and 6 h, resulting in cumulative mortalities of 5 and 35%, respectively. No mortality was observed in the rainbow trout groups immersed with the genotype III VHSV isolate 4p168 for 1 and 6 h. The viral titre in organs from fish challenged with NO-2007-50-385 for 6 h increased more rapidly than those exposed for 1 h. By in vitro studies it was demonstrated that the final titres of VHSV DK-3592B (GI), NO-2007-50-385 and 4p168 inoculated on EPC cells were very similar, whereas when inoculated on the rainbow trout cell line RTG-2 the titre of the non-virulent 4p168 isolate was 3-4 logs below the two other VHSV isolates. Based on a comparative analysis of the entire genome of the genotype III isolates, we suggest that substitutions of amino acids in positions 118-123 of the nucleo-protein are candidates for being related to virulence of VHSV GIII in rainbow trout.
authors.affiliation: Tamaki Laboratory, Aquatic Animal Health Division, National Research Institute of Aquaculture, Fisheries Research Agency, 224-1 Hiruda, Tamaki, Mie, Japan. takafumi@fra.affrc.go.jp.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ito
authors.affiliation: Tamaki Laboratory, Aquatic Animal Health Division, National Research Institute of Aquaculture, Fisheries Research Agency, 224-1 Hiruda, Tamaki, Mie, Japan. kuritaj@fra.affrc.go.jp.
authors.forename: Jun
authors.initials: J
authors.lastname: Kurita
authors.affiliation: Aquatic Animal Health Division, National Research Institute of Aquaculture, Fisheries Research Agency, 422-1 Nakatsuhamaura, Minami-Ise, Mie, Japan. mori516@affrc.go.jp.
authors.forename: Koh-ichiro
authors.initials: K
authors.lastname: Mori
authors.affiliation: National Veterinary Institute, Technical University of Denmark, Bülowsvej 27, 1870, Frederiksberg C, Denmark. njol@vet.dtu.dk.
authors.forename: Niels J
authors.initials: NJ
authors.lastname: Olesen
mesh_terms: D000818:Animals; D002460:Cell Line; D005393:Fish Diseases / Q000821:virology*; D005838:Genotype; D029141:Novirhabdovirus / Q000235:genetics* / Q000472:pathogenicity*; D017686:Oncorhynchus mykiss; D014774:Virulence; D014779:Virus Replication / Q000502:physiology