Temperature, pH and electrolyte sensitivity, and heat, UV and disinfectant inactivation of sea bass ( Dicentrarchuslabrax) neuropathy nodavirus

The effect of temperature, pH and electrolytes on the stability of two Mediterranean sea bass neuropathy nodavirus isolates (SBNN) and the inactivation of SBNN by heating, exposure to ultraviolet radiation and chemical disinfectants was investigated in vitro using a striped snakehead fish cell line (SSN-1) for virus propagation and assay. The two nodavirus isolates showed no significant differences in response to the procedures examined. Nodavirus held in cell culture medium containing 5% foetal bovine serum was effectively inactivated within 4 days at 37°C and 3 months at 25°C but showed no significant loss of titre over 6 months at 15°C and still retained a measurable level of infectivity after storage for 1 year at this temperature. Virus suspensions in distilled water tolerated exposure to pH 2–11 with no significant loss of titre over 24 h. Thereafter, a steady diminution in infectivity was noted at pH 11 from day 3 and at pH 2 from day 15 onwards, but no loss of titre was recorded between pH 3–7 over 6 weeks storage. Infectivity titres fell gradually at a very similar rate for virus held at 15°C in balanced salt solution and full- and half-strength seawater over a 6-month test period. Virus held in freshwater, however, was markedly less stable and no viable virus could be detected after 6 months storage. SBNN was susceptible to heat treatment at 60°C within 30 min with no viable virus detected after 1 h. UV irradiation at an intensity of 440 μW/cm 2 resulted in a 99.9% linear reduction in virus titre after 8 min exposure. Treatment with 2% formalin was not totally effective even after 6 hours exposure at 15°C although virus titre was reduced. The effect of chlorine, iodine and peroxygen on SBNN at 15°C was noticeably different when organic matter in the form of foetal bovine serum (FBS) was present in the virus diluent. Suspensions of virus in distilled water were completely inactivated within 5 min by 50 ppm chlorine and 25 ppm iodine. Virus in Hanks' BSS+FBS, however, showed only a marginal loss in infectivity following similar treatments and significant levels of infectivity were still detectable after 30 min exposure to 100 ppm of either disinfectant. Treatment with an acid peroxygen disinfectant rapidly reduced virus infectivity in both distilled water and serum supplemented diluent within 5 min but infectious virus was not totally eliminated even after exposure for 30 min.