Effect of various treatments on white spot syndrome virus (WSSV) from Penaeus japonicus (Japan) and P-monodon (Thailand)

Two causative agents of white spot syndrome (WSS), penaeid rod-shaped DNA virus (PRDV) from infected kuruma shrimp (Penaeus japonicus) in Japan and systemic ectodermal and mesodermal baculovirus (SEMBV) from black tiger shrimp (P. monodon) in Thailand, were tested for their sensitivities to chemicals, temperature, drying and singlet oxygen (O-1(2)). The infectivity of the treated PRDV and SEMBV was determined by challenge tests in kuruma shrimp and black tiger shrimp, respectively. Sodium hypochlorite inactivated PRDV at 1 ppm for 30 min and at 5 ppm for 10 min. SEMBV was inactivated by sodium hypochlorite at 10 ppm for 30 min. Povidone-iodine inactivated these viruses at a concentration of 10 ppm for 30 min. A high concentration of NaCl (12.5%) inactivated PRDV in 24 h at 25 degrees C, and 15% NaCl inactivated SEMBV in 24 h at 28 degrees C. PRDV was inactivated by heating at 50 degrees C for 20 min, by drying at 30 degrees C, and by using ethyl ether. PRDV in the sea water maintained its infectivity for at least 120 days at 4 degrees C, and for more than 60 days but less than 120 days when kept at 25 degrees C. However, PRDV, when suspended in sea water at a lower concentration, maintained infectivity for 10 days at 4 degrees C and for 7 days at 25 degrees C. SEMBV maintained infectivity in sea water for 5 days at 28 degrees C PRDV was exposed to O-1(2), which was generated by an insoluble dye (rose bengal) and visible light. Shrimp that received O-1(2)-exposed virus showed lower mortality than control shrimp, indicating that O-1(2) inactivated PRDV. This O-1(2) generating system is a simple, safe and effective technique that can be applied to aquaculture.