Disease due to infection by spawner-isolated mortality virus ( SMV ) was first recognised in captive spawners of Penaeus monodon at a research station in northern Queensland, Australia.
SMV is one of several viruses associated with mid-crop mortality syndrome ( MCMS ) , which caused significant mortalities among cultured juveniles and subadults of P. monodon cultured in Australia from 1994 to 1996. In the Philippines, P. monodon infected with luminous vibriosis were also found to be infected with SMV ( 1 ) . Infection and disease due to SMV has only been reported from cultured or captive wild adult P. monodon and cultured Cherax quadricarinatus( 4 ) .
SMV has been tentatively classified as a parvovirus ( 2 ) . Transmission electron microscopy of infected P. monodon showed virus particles that were 20 nm in diameter, hexagonally shaped, and suggestive of an icosahedral symmetry. Accumulations of these 20 nm particles in massive arrays were noted in the cytoplasm of infected gut cells, and the virions appeared to be issuing through pores in the nuclear membrane ( 2 ) . Partial characterisation of the virus was accomplished by treatment of infected prawn tissue extracts with DNase and RNase. These tests further indicated that SMV is a DNA virus, probably a parvovirus ( 2 ) .
There are no practical surveillance methods presently available for SMV in penaeid prawns. Confirmatory diagnosis of SMV can be accomplished by transmission electron microscopy of gut tissues.