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Diseases of Aquatic Organisms

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DAO 43:1-14 (2000)  -  doi:10.3354/dao043001

First isolation of an aquatic birnavirus from farmed and wild fish species in Australia

Mark St. J. Crane1,*, Paul Hardy-Smith2,**, Lynette M. Williams1, Alex D. Hyatt1, Lauretta M. Eaton1, Allan Gould1, Judith Handlinger3, Jackie Kattenbelt1, Nicholas Gudkovs1

1Australian Animal Health Laboratory, CSIRO Livestock Industries, Private Bag 24, Geelong, Victoria 3220, Australia
2Department of Primary Industries, Water and Environment, 13 St Johns Avenue, Newtown, Tasmania 7008, Australia
3Mount Pleasant Laboratories, Department of Primary Industries, Water and Environment, PO Box 46, Kings Meadows, Tasmania 7249, Australia
*E-mail: **Present address: Heritage Aquaculture Suite #203, 919 Island Highway, Campbell River, British Columbia V9W 2C2, Canada

ABSTRACT: During routine sampling and testing, as part of a systematic surveillance program (the Tasmanian Salmonid Health Surveillance Program), an aquatic birnavirus was isolated from Œpinhead¹ (fish exhibiting deficient acclimatisation on transfer to saltwater) Atlantic salmon Salmo salar, approximately 18 mo old, farmed in net-pens located in Macquarie Harbour on the west coast of Tasmania, Australia. The isolate grows readily in a range of fish cell lines including CHSE-214, RTG-2 and BF-2 and is neutralised by a pan-specific rabbit antiserum raised against infectious pancreatic necrosis virus (IPNV) Ab strain and by a commercial pan-specific IPNV-neutralising monoclonal antibody. Presence of the virus was not associated with gross clinical signs. Histopathological examination revealed a range of lesions particularly in pancreatic tissue. The virus was localised in pancreas sections by immunoperoxidase staining using the polyclonal antiserum and by electron microscopy. Examination by electron microscopy demonstrated that the virus isolated in cell culture (1) belongs to the family Birnaviridae, genus Aquabirnaviridae; (2) was ultrastructurally and antigenically similar to virus identified in the index fish; (3) is related to IPNV. Western blot analysis using the polyclonal rabbit antiserum confirmed the cross-reactions between various aquatic birnavirus isolates. In addition, PCR analysis of isolated viral nucleic acid from the index case indicated that the virus is more closely related to IPNV fr21 and N1 isolates than to other birnavirus isolates available for comparison. Sampling of other fish species within Macquarie Harbour has demonstrated that the virus is present in several other species of fish including farmed rainbow trout Oncorhynchus mykiss, wild flounder Rhombosolea tapirina, cod Pseudophycis sp., spiked dogfish Squalus megalops and ling Genypterus blacodes.

KEY WORDS: Virus isolation · Aquatic birnavirus · Farmed fish · Wild fish · Australia · Infectious pancreatic necrosis · IPNV · PCR

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