Identification of White Spot Syndrome Virus Homologues in the Genome of Kuruma Shrimp

Viral diseases are the most serious problems in shrimp aquaculture. One of these viral diseases is white spot disease. The causative agent of white spot disease is white spot syndrome virus (WSSV), which is highly virulent to penaeid shrimp. It is therefore important to understand the interaction between shrimp and virus to develop effective strategies against WSSV infection. The current study has found WSSV homologues in the kuruma shrimp, Marsupenaeus japonicus genome. Functional analysis of these WSSV homologues and their relationship to WSSV infection was examined. Two genes, c13wsv440 and c65wsv360_2, were expressed in hemocytes, stomach, intestine, heart and nerve and hemocytes, gills, lymphoid organ, stomach, intestine, hepatopancreas, heart and nerve, respectively. These gene expressions in hemocytes, gills and stomach were increased significantly after WSSV infection. Cumulative mortality of c13wsv440-silenced shrimps was not significantly different to that of the PBS-injected group (negative control). The WSSV copy numbers of this group were also not significantly different to that of the PBS-injected group. Meanwhile, the c65wsv360_2-silenced shrimps had significantly lower mortality compared to that of PBS-injected group. The WSSV replication in this silenced group was inhibited significantly. These findings suggest that WSSV homologues interact with WSSV affecting its infectivity. c13wsv440 may be related to defense mechanism in kuruma shrimp while c65wsv360_2 may provide support for the pathogenicity of WSSV.