During mortality outbreaks in hatchery-reared Macrobrachium rosenbergii postlarvae (PL) in Guadeloupe Island (French West Inbes) during 1997, an associated viral disease was discovered and the agent was subsequently isolated. The clinical signs presented by severely affected PL consisted essentially of an opaque whitish appearance of the abdomen. Histopathological changes in affected PL were characterized predominantly by pale to darkly basophilic, often reticulated, cytoplasmic inclusions in the connective tissue cells of most organs and tissues. The isolated virus was approximately 30 nm in diameter as observed with an electron microscope by negative staining. By its location, structure and size it could be related to different families of the small RNA cytoplasmic viruses such as the Picornaviridae or the Nodaviridae. Its characterization is in progress.

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Since 1997, slm~lar baculo\~iruses, w h~c h cause hlgh mortaht~es In p e n a e~d shrlmp, have been reported from Chlna, Japan, Korea, Thailand and T d~w a n All these baculov~rus-caused d~s e a s e s are characterlzed by the presence of w h~t e spots in the cutlcle To lsolate the agent of the dlsease referred to as Whlte Spot Syndrome (WSS) and W h~t c Spot Baculovlrus (WSBV], In t h~s paper, Penaeus van name^ and P styl~rostns were expcr~rnentally inoculated with homogenates ot infected Penaeus monodon from Thalland In t~ansmlsslon clectron nllcroscopy (TEM) the enveloped WSB\ v~~~o n s have a s u e of about 350 nm long and 130 nm wlde The nucleocapsids langc from 300 to 420 nm in length and 70 to 95 nm In diameter and show a supe~f~clally segmented appearance Also present are unique paltlcles, w h~c h have not been observcd beforc, measuring 400 nm In length and 120 nm in w~d t h These particles are l a g e r than most of the usudl nucleocdpsids and have a cross

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