Monodon baculovirus (MBV) infects the freshwater prawn Macrobrachium rosenbergii cultivated in Thailand.

Field specimens of post-larvae of the giant freshwater prawn (Macrobrachium rosenbergii) from Thailand showed hepatopancreatic tubule epithelial cells that contained central, eosinophilic inclusions within enlarged nuclei and marginated chromatin. These inclusions resembled those produced by some baculoviruses prior to formation of occlusion bodies that enclose virions in a polyhedrin protein matrix. By electron microscopy, the intranuclear inclusions contained bacilliform, enveloped virions (approximately 327+/-29nmx87+/-12nm) with evenly dense, linear nucleocapsids surrounded by trilaminar envelopes with lateral pockets containing nucleoproteinic filaments. In some cases, these were accompanied by moderately electron dense, spherical particles of approximately 20nm diameter resembling polyhedrin subunits of occlusion bodies (OB) of a bacilliform virus of the black tiger shrimp Penaeus monodon, previously reported from Thailand and called monodon baculovirus (MBV). It is currently listed by the International Committee on Taxonomy of viruses as Penaeus monodon nucleopolyhedrovirus (PemoNPV). Two polymerase chain reaction (PCR) assays for MBV gave positive results with DNA extracts prepared from M. rosenbergii samples using the hot phenol technique. One of these assays targeted the polyhedrin gene of MBV to which the resulting amplicon showed 100% sequence identity. Presence of the Penaeus monodon virus polyhedrin gene was confirmed by in situ hybridization assays and by positive immunohistochemical reactions in one sample batch. The data revealed that MBV can be found but may rarely produce polyhedrin occlusion bodies in M. rosenbergii.

Parvo-like virus in the hepatopancreas of freshwater prawns Macrobrachium rosenbergii cultivated in Thailand.

A survey of cultivated giant freshwater prawns Macrobrachium rosenbergii from Thailand revealed the presence of unusual spherical to ovoid inclusions in nuclei of hepatopancreas tubule epithelial cells. These began as small eosinophilic inclusions that became more basophilic as they increased in size. They were present in both R-cells and E-cells but were largest and deeply basophilic only in the E-cells. Confocal laser microscopy revealed that stained nucleic acid fluorescence from the inclusions was lost by treatment with DNase I specific for double- and single-stranded DNA and also lost or reduced by treatment with mungbean nuclease specific for single-stranded nucleic acids. Transmission electron microscopy (TEM) revealed that the inclusions contained tightly packed, unenveloped, viral-like particles of approximately 25 to 30 nm diameter, resembling those produced by shrimp parvoviruses. However, PCR, in situ hybridization and immunohistochemical tests for shrimp parvoviruses previously reported from Thailand were all negative. These results suggested that the inclusions contained a parvo-like virus, not previously reported from M. rosenbergii in Thailand.