The susceptibility of three species of marine shrimp (Penaeus indicus, Penaeus japonicus and Penaeus monodon) to Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV) was tested by oral route and intramuscular injection. The results revealed that these marine shrimp were not susceptible to these viruses which failed to produce mortality in shrimp. RT-PCR analysis revealed the presence of MrNV and XSV in different organs such as gill, abdominal muscle, stomach, intestine and hemolymph of three species of shrimp injected with viruses. These viruses were also found in different tissues of shrimp fed with WTD-infected prawn meat, but not in control groups fed with uninfected meat. The reinoculation studies using the inoculum of MrNV and XSV prepared from marine shrimp caused 100% mortality in the post-larvae of freshwater prawn and the moribund post-larvae showed positive for these viruses by RT-PCR. The results of present study indicate the possibility of marine shrimp acting as reservoir for MrNV and XSV and maintaining their virulence in tissue system of marine shrimp. © 2006 Elsevier B.V. All rights reserved.