A YELLOW-HEAD LIKE VIRUS FROM PENAEUS-MONODON CULTURED IN AUSTRALIA

A rod-shaped, gill-associated virus (GAV) was found to be associated w ith mortalities of cultured adult Penaeus monodon from 4 farms in Quee nsland, Australia, from January to June 1996. infected prawns were obs erved swimming at the surface and edges of ponds and displayed varying degrees of red body colouration. The lymphoid organs of infected praw ns appeared disorganized, were devoid of normal tubule structure and c ontained highly eosinophilic areas which corresponded to foci of highl y infected and necrotic cells. Rod-shaped, enveloped virions and helic al nucleocapsids were identified in lymphoid organ and gill cells. Nuc leocapsids were 166-435 nm x 16-18 nm and enveloped virions were 183-2 00 nm x 34-42 nm. GAV isolated from infected prawns collected from 3 f arms was successfully transmitted to healthy adult P. monodon, resulti ng in mortality from 7 to 8 d postinoculation. Mortality also occurred in prawns infected experimentally with GAV derived from lymphoid orga ns and gills. The morphology and cytopathology of GAV closely resemble that observed for lymphoid organ virus (LOV) from Australia and yello w-head virus (YHV) from Thailand. Molecular data are required to deter mine the phylogenetic relationships and appropriate taxonomic classifi cation of these 3 prawn viruses.