Atlantic salmon papillomatosis in Russia and molecular characterization of the associated herpesvirus.

Papillomatosis of Atlantic salmon Salmo salar has been reported for decades in Russia, Scandinavia and Scotland. The disease is typically benign although heavy losses have occasionally been reported. A herpesviral etiology has been suggested based on ultrastructural evidence; however, the virus has not been isolated or genetically characterized. In this study, we provide the first viral sequences detected in the papillomas from diseased Russian Atlantic salmon. Phylogenetic analyses, based on the partial sequences of the herpesviral polymerase and terminase genes, supported the virus as a novel member of the genus Salmonivirus within the family Alloherpesviridae. The sequences of the Atlantic salmon papillomatosis virus differ markedly from those of the 3 known salmoniviruses; therefore, the authors propose the species designation Salmonid herpesvirus 4 to be considered for approval by the International Committee on Taxonomy of Viruses.

Partial genome analysis of Siberian sturgeon alloherpesvirus suggests its close relation to AciHV-2 - short communication.

Partial genome sequence of a herpes-like virus, isolated from Siberian sturgeon (Acipenser baeri), was determined and subjected to phylogenetic analysis. The virus (SbSHV) has been shown to be the causative agent of an acute disease with high mortality in farmed juvenile sturgeons in Russia. Two fragments (of 7000 and 300 base pairs in length) encompassing 3 complete and 3 partial ORFs were amplified by PCR. Sturgeon herpesvirus strains, classified into species Acipenserid herpesvirus 2 (AciHV-2), have been isolated and partially sequenced from several regions (California, Idaho, Oregon and Canada) of North America from white (A. transmontanus) and shortnose sturgeons (A. brevirostrum). The sequence of the SbSHV strain shared highest identity with that of the Canadian strain originating from shortnose sturgeon. The phylogenetic analysis also confirmed that SbSHV is closely related to AciHV-2 and could also be classified into this virus species. This is the first report on the occurrence of AciHV-2 in Europe. Previously, only another virus species, AciHV-1 has been detected in farmed white sturgeons in Italy. The size and position of ORFs in the examined gene block confirmed that this genomic region is highly conserved in members of the genus Ictalurivirus.

First detection of a viral agent causing disease in farmed sturgeon in Russia.

A virus was isolated from Siberian sturgeon Acipenser baeri and bester (beluga Huso huso x sterlet A. ruthenus hybrid) fingerlings in SSO-2, SSF-2 and WSSK-1 cell lines during an acute epizootic on a large fish farm producing fertilised sturgeon eggs and fry. Transmission electron microscopic examination of samples from both inoculated cell cultures and skin of affected fish revealed viral particles with a herpesvirus-like morphology. The etiological role of the Siberian sturgeon herpesvirus (SbSHV) was confirmed by fulfilment of Rivers' postulates. Experimental immersion of healthy Siberian sturgeon fingerlings in a suspension of SbSHV resulted in 100% mortality with signs of focal epidermal hyperplasia, skin necrosis and multiple skin haemorrhages. While infecting different organs and tissues, the virus showed clear integumentary tropism. Carp fry and rainbow trout fingerlings were neither susceptible to the virus nor did they transmit it to healthy Siberian sturgeon.