Fish Diseases and Management

5.4.5.2 Monodon type baculoviruses

MBV enjoy a world-wide distribution, on the Indo pacific coast of Asia, Antarctica, Africa and Southern Europe and have a diverse host range. Another viral agent called Plebejus baculovirus (PBV) found in cultured penaeids in Australia is reported to be probably a different strain of MBV. These are type A baculoviruses measuring 75 x 324. MBV infections are diagnosed by the presence of single or multiple, generally spherical occlusion bodies in hepatopancreas and midgut epithelial cells. MBV occlusions in squash preparation can be easily visualized by 0.05% aqueous malachite green staining, epifluorescence microscopy and acridine orange staining. The occlusion bodies contain randomly occluded enveloped virus aggregations of MBV virions especially near to the nuclear membrane. Virogenic stroma is often found at the centre of the nucleus while the nucleolus will be marginated to the inner surface of nuclear membrane and get modified to form virogenic stroma.

MBV was first discovered in a quarantined population of P. monodon that had originated from Taiwan. Currently, the virus is found distributed in Taiwan, Japan, Philippines, Indonesia and generally throughout Indo pacific. Despite its distribution around the world, the virus is not a highly virulent pathogen of P. monodon. MBV is found in healthy prawns and in disease epizootics. P. monodon has been found to frequently have mixed infections by MBV and other viral, bacterial or protozoan pathogens.