Isolation and characterisation of a marine birnavirus from returning Quinnat salmon (Oncorhynchus tshawtscha) in the South Island of New Zealand

We record here the first isolation of a birnavirus from fish in Australasia. The virus was isolated from a Quinnat salmon (Oncorhynchus tshawtscha) returning up the Rakaia River. The salmon was included in a group of normal fish being tested for viral haemorrhagic septicaemia virus for export certification. Kidney and spleen samples were homogenized using Ten Broeck grinders, diluted 1:10 in phosphate buffered saline (pH 7.6) containing gentamycin (100 g/ml) and amphotericin B (5 pg/ml) and centrifuged for 10 minutes at 1500 g. Monolayers of Rainbow trout gonad (RTG-2) and Fat Head minnow (FHM) cells in microtitre plates were inoculated with 1: 1000 dilution of the homogenized tissue suspension and absorbed for one hour at 15°C. The monolayers were then overlaid with Eagles minimal essential media (Earles salts) contining 2% fetal calf serum, 16 mM Tris buffer (pH 7.6) and gentamycin (100 g/ml). Cultures were incubated at 15°C and were passaged at 14 day intervals. A cytopathic effect as observed during the second passage in RTG-2 cells and was subsequently reproduced by…