A recently repor1t.d dlsease s y n d~o m e of Penaeus monodon In Thalland IS called 'yellow-head' or hua leung In Thal It is usually charactenzed by llght yellow coloratlon of the dorsal cephalothorax area and generally pale or bleached appearance of a f f~c t e d prawns The yellow color In the cephalothorav reglon iesults from the underlying y e l l o~~ hepatopancreas showlng through the translucent carapace In m o~i b u n d shrimp In h~stological prepdrations of moribund yellow-head specimens for the light mlcloscope. no consistent bacteiial fungal or parasltlc agents could be found The lylnphold organs ot yellow-head specimens sho\ved extensive abnormalities These Included obv~ously necrotlc cells and vacuolated cells with hypertrophied nuciel Also evldent were vely densely basophil~c, globose cytoplasmic ~nclusions located adjacent to some ot the hypertroph~ed nuclei Slrn~lar basophil~c inclusions were found In interst~tl~il hepatopancreat~c tissue In connective tlssue u n d e~ lylng the mld gut, In cardlac tissue, In glll t~s s u e and In hematopoetlc tissue T l a n s m~s s~o n electron mlclographs revealed the presence of pic\iously undescrlbed rod-shaped, enveloped virions in the cytoplasm adjacent to the nuclei of cells f~ om various tissues Free vlnons \yere also present In intercellular spaces The virions were s~r n d a to those of the ~tlsect grahulosls vlruses (Baculov~r~dae) In terms of cytoplasmic locatlon size, morphology and development. However, they were not occluded by granulln
A new non-occluded baculo-like virus was detected from black tiger shrimp (Penaeus monodon) with yellow head disease in the southern part of Thailand. Virus particles observed in necrotic tissues of gills and lymphoid organ were bacilliform in shape, ranging from 150-200 nm in length and 40-50 nm in diameter, and were enveloped singly by a trilaminar unit membrane. From the experimental infection trials, it was assumed that this virus was the most virulent among the viruses which have been known in the black tiger shrimp, to date. Pathogenicity and some characters of the virus as well as pathological changes caused by this virus were described.
A picorna-like virus was detected from diseased fry and fingerling grouper Epinephelus malabaricus cultured in southern Thailand. Affected grouper exhibited dark coloration of the head and tail, loss of equilibrium and corkscrew-like swimming. Pathological changes of affected fish showed vacuolating encephalopathy and retinopathy. Intracytoplasmic inclusions were observed in the nerve cells. From electron microscopic studies, virus particles could be detected in the brain and eyeball of affected fishes. They were round to icosahedral, without an envelope, 20 to 25 nm in diameter and had an electron dense core of 16 nm. Filtrates (0.45 pm) of affected brain and eyeball tissues can produce the same clinical signs in healthy grouper after injection, and the identical virus particles could be observed in the brain and retina of experimentally infected fish.
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