Quasi-immune response of Penaeus japonicus to penaeid rod-shaped DNA virus(PRDV)

A quasi-immune response was demonstrated in kuruma prawn Penaeus japonicus infected naturally or experimentally with PRDV (penaeid rod-shaped DNA viru s, also called white spot syndrome virus or WSSV), the causative agent of P AV (penaeid acute viremia). In the first step of this study, natural surviv ors 4 mo after a PAV outbreak demonstrated 94 % relative percent survival ( RPS) upon experimental PRDV challenge. Mortalities after challenge were con firmed by PRDV detection to be due to PAV using a PCR method. In the second step, experimental PAV survivors were produced by intramuscular (IM) injec tion of PRDV into naive shrimp subsequently reared collectively in a tank ( A group) or individually in chamber units (B group). Survival was 41 and 90 % in the A and B groups, respectively. A subsequent IM re-challenge of the se PRDV survivor groups with PRDV made 32 d after the first challenge revea led a protective response with high RPS of 77 and 64 %, respectively. These high survival rates suggested that PAV survivors (natural or experimental) were able to resist PRDV infection and that the resistance was not due to selection of naturally resistant shrimp during a PAV outbreak, but due to e nhancement of an immune-like system (quasi-immune response) after exposure to PRDV. No PRDV neutralizing activity was revealed in the serum of the 4 m o natural survivors of the PRDV outbreak. However, it was found in their se rum 17 d after they had been experimentally challenged with PRDV.