Spawner-isolated mortality virus from australian Penaeus monodon

Abstract

In 1993, an epizootic occured in captive Penaeus monodon spawners at aresearch facility in northern Queensland, Australia. The spawners exhibitedlethargy, failure to feed, redness of the carapace and pleiopods, and anincreased mortality rate A reliable bioassay of 0.45 μm filtered, cell-freeextracts of infected tissue produced mortalities approaching 100% ininoculated prawns. On average, the infected prawns became dark red by Day 6,produced red faeces by Day 10 and first mortalities by Day 13. Red faeces wasa feature of this disease that has not been previously reported. When thesurvival curves of a dietary route were compared to the inoculation routerthere was a lag period of 21 d. After subtraction of 21 d, the survivalcurves were statistically the same (G = 1.284, df = 1, p > 0.05).Pathological changes were found in the subcuticular epithelium and underlyingmuscle, depleted haematopoietic tissue, lymphoidal organ, hepatopancreas andgut. Increased eosinophilic refractile material was observed in thesubcuticular epithelium and basement membrane and in the capsule surroundingthe hepatopancreas. There were extensive areas of haemocytic infiltration andmelanisation of the subcuticular epithelium with haemolytic replacement andnecrosis of the underlying muscle. There were large areas of necrosis in thehepatopancreas, as cells with pyknotic nuclei sloughed into the lumen. Small(20 nm) icosahedral virions were observed in gut cells with transmissionelectron microscopy, and partial characterisation indicated that it was anonenveloped DNA virus, similar to a parvovirus.