Histology and ultrastructure reveal a new granulosis-like virus in Penaeus monodon affected by yellow-head disease

A recently repor1t.ddlsease 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 extensive abnormalities These Included obv~ously necrotlc cells and vacuolated cells with hypertrophied nuciel Also evldent were vely densely baso-phil~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 undescrlbed rod-shaped, enveloped virions in the cytoplasm adjacent to the nuclei of cells f~ om various tissues Free vlnons 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