Spawner-isolated mortality virus from Australian Penaeus monodon

In 1993, an epizootlc occurred in captive Penaeusmonodon spawners at a research facility In northern Queensland.Australia The spawners exhib~ted lethargy, failuie to feed redness of the carapace and pleiopods, a n d an incieased mortality rate A reliable bioassay of 0 4 5 pm filtered, cellfree extracts of infected tissue produced mortalities approaching 100% In inoculated prawns O n average the Infected prawns became dark red by Day 6, produced red faeces by Day 10 and first mortal~tles by Day 13 Red faeces was a feature of thls dlsease that has not been previously reported When the survlval curves of a dietary route weie compared to the inoculation route there was a lag perlod of 21 d After subtraction of 21 d, the surv~val curves were statistically the same (C = 1 284, df = l , p > 0 05) Pathological changes were found in the subcut~cular epithelium and underly~ng muscle depleted haematopoletic tissue lymphoidal organ, hepatopancreas and gut Increased eosinophilic refractile matenal was observed in the subcuticular epithelium and basement membrane and in the capsule surrounding the hepatopanci eas There were extensive areas of haemocytic ~nflltration and melanisation of the subcut~culai eplthellum with haemocytlc replacement and necrosls of the underlying muscle Theie were large areas of necrosis In the hepatopancieas, as cells wlth pyknotlc nuclei sloughed into the lumen Small (20 nm) icosahedral vlrions were observed in gut cells w ~t h transmission electron microscopy, and partial charactensat~on Indicated that it was a nonenveloped DNA virus.similar to a parvovirus KEY WORDS-Penaeus monodon .