A yellow-head like virus from Penaeus monodon cultured in Australia

Abstract

A rod-shaped, gill-associated virus (GAV) was found to be associated with mortalities of cultured adult Penaeus monodon from 4 farms in Queensland, Australia, from January to June 1996. Infected prawns were observed swimming at the surface and edges of ponds and displayed varying degrees of red body colouration. The lymphoid organs of infected prawns appeared disorganized, were devoid of normal tubule structure and contained highly eosinophilic areas which corresponded to loci of highly infected and necrotic cells. Rod-shaped, enveloped virions and helical nucleocapsids were identified in lymphoid organ and gill cells. Nucleocapsids were 166-435 nm x 16-18 nm and enveloped virions were 183-200 nm x 34-42 nm. GAV isolated from infected prawns collected from 3 farms was successfully transmitted to healthy adult P. monodon, resulting in mortality from 7 to 8 d post-inoculation. Mortality also occurred in prawns infected experimentally with GAV derived from lymphoid organs and gills. The morphology and cytopathology of GAV closely resemble that observed for lymphoid organ virus (LOV) from Australia and yellow-head virus (YHV) from Thailand. Molecular data are required to determine the phylogenetic relationships and appropriate taxonomic classification of these 3 prawn viruses.