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Diseases of Aquatic Organisms

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DAO 114:117-125 (2015)  -  DOI:

Isolation of a novel aquatic birnavirus from rainbow trout Oncorhynchus mykiss in Australia

Christina McCowan1,*, Julian Motha1, Mark St. J. Crane2, Nicholas J. G. Moody2, Sandra Crameri2, Alex D. Hyatt2, Tracey Bradley3

1Victorian Department of Economic Development, Jobs, Transport and Resources, Agriculture Productivity Division, 5 Ring Road, Bundoora, Victoria 3083, Australia
2CSIRO Australian Animal Health Laboratory, 5 Portarlington Road, Geelong, Victoria 3220, Australia
3Victorian Department of Economic Development, Jobs, Transport and Resources, Regulation and Compliance Group, 475 Mickleham Rd, Attwood, Victoria 3049, Australia
*‑Corresponding author:

ABSTRACT: In November 2010, a rainbow trout (Oncorhynchus mykiss) hatchery in Victoria reported increased mortality rates in diploid and triploid female fingerlings. Live and moribund fish were submitted for laboratory investigation. All fish showed hyperpigmentation of the cranial half of the body. Histological lesions were seen in all areas of skin examined despite the localised nature of the gross lesions. There was irregular hyperplasia and spongiosis, alternating with areas of thinning and architectural disturbance. Occasionally, particularly in superficial layers of epithelium, cells showed large, eosinophilic inclusions that obscured other cellular detail. A small number of fish had necrosis in dermis, subcutis and superficial muscles. Bacteriological culture of skin and gills was negative for all bacterial pathogens, including Flavibacterium columnare, the agent of columnaris disease. Attempts at virus isolation from the skin of affected fish resulted in the development of a cytopathic effect in RTG-2 cell cultures suggestive of the presence of a virus. Negative contrast electron microscopy of cell culture supernatant demonstrated the presence of viral particles with the typical morphology of birnaviruses. Preliminary molecular characterisation identified an aquabirnavirus that differed from both the Tasmanian aquabirnavirus (TABV) and other aquabirnaviruses exotic to Australia. Previous isolates of aquabirnaviruses in Australia and New Zealand have been from healthy fish in a marine environment. This is the first report of an aquabirnavirus isolated from young salmonids at a freshwater hatchery in Australia. The role of the virus in the mortality event on the farm is uncertain as no further deaths attributable to this virus have occurred in the 4 yr since its initial discovery. The virus has been provisionally named Victorian trout aquabirnavirus (VTAB).

KEY WORDS: Aquabirnavirus · Rainbow trout · Oncorhynchus mykiss · Australia

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Cite this article as: McCowan C, Motha J, Crane MSJ, Moody NJG, Crameri S, Hyatt AD, Bradley T (2015) Isolation of a novel aquatic birnavirus from rainbow trout Oncorhynchus mykiss in Australia. Dis Aquat Org 114:117-125.

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