Crayfish Procambarus clarkii protected against white spot syndrome virus by oral administration of viral proteins expressed in silkworms

Although it is generally accepted that invertebrates do not have a true adaptive immune response system such as that present in vertebrates, we investigated the potential of oral administration of WSSV envelope proteins to Procambarus clarkii crayfish for protection against white spot syndrome virus. Proteins used included VP28 and VP19 expressed in silkworm using a baculovirus (HyNPV) expression system in order to gain correctly folded proteins with biological activity. Procambarus clarkii were fed pellets coated with silkworm homogenate containing the two recombinant proteins. The tested crayfish showed a significantly better survival (P < 0.05) when compared to the control crayfish fed wild-type HyNPV baculovirus-infected silkworms. The relative percent survivals (RPS) were 94.7% (VP28) and 89.5% (VP19). Also, the groups fed a mixture of VP28 and VP19 showed a significantly higher survival (RPS, 96.5%) than the control. These results show that protection can be generated against WSSV using envelope proteins. Although the mechanism of protection is unknown, the results suggested that limited protection against WSSV provided by envelope proteins might be possible in decapod crustaceans.