Duration and Booster Effect of Phylactic Response against White Spot Syndrome Virus Infection in Kuruma Shrimp Orally Administrated with Recombinant Viral Proteins, rVP26 and rVP28

White spot syndrome virus (WSSV: a synonym of penaeid rod-shaped DNA virus, PRDV) is the causative agent of white spot disease (WSD: penaeid acute viremia, PAV), one of the most serious diseases affecting decapod crustaceans around the world. Recently, "quasi-immune response" was found in kuruma shrimp Penaeus japonicus, wherein individuals that naturally survived from WSD showed protection against a rechallenge with WSSV. The phylaxis against WSSV was also inducible by oral vaccination with recombinant WSSV proteins, rVP26 and rVP28. In the present study, kuruma shrimp orally vaccinated with rVPs were sequentially challenged with WSSV to evaluate onset and duration of phylactic response and booster effect. The phylactic response of shrimp against WSSV-challenge peaked at day 45 after the vaccination with rVP26 (RPS: 100%) and at day 55 with rVP28 (RPS: 93%), and decreased within 10-20 days. The phylaxis against WSSV-challenge was boosted by the secondary vaccination with homologous rVPs, but not by those with heterologous rVPs. The peaks of phylactic responses appeared at day 22 after the secondary vaccination more rapidly than those after the primary vaccination. These results demonstrated that the duration of phylaxis induced by oral vaccination with rVPs was relatively short, but could be extended by booster vaccination with homologous rVPs.