LYMPHOIDAL PARVOVIRUS-LIKE PARTICLES IN AUSTRALIAN PENAEID PRAWNS

Prawns in northern Queensland exhibited multinucleated giant cell formation in hypertrophied lymphoid organs. Mostly farmed Penaeus monodon, P. merguiensis and P. esculentus were involved. The transformation involved mild nuclear hypertrophy, marginated chromatin and basophilic darkening of increased cytoplasm in a multinucleate giant cell. Areas of transformation were discrete, often bounded by elongated fibrocytes and sometimes fully encapsulated. Basophilic inclusions occurred commonly and eosinophilic intranuclear inclusions rarely. These inclusions stained for DNA with acridine orange fluorescence. Associated with lymphoidal changes was the presence of rounded F-like cells with basophilic, pyknotic nucleoli. Under the electron microscope, transformed lymphoidal cells displayed virus-like particles of 18 to 20 nm diameter associated with inclusion bodies in the nucleus. These particles were similar to a parvovirus and named lymphoidal parvovirus-like (LPV). Their similarities and relationship to hepatopancreatic parvovirus and infectious hypodermal and haematopoietic necrosis virus are discussed.