Practical Aspects of Survival and Destruction of Infectious Pancreatic Necrosis Virus

Abstract

The survival of infectious pancreatic necrosis (IPN) virus under conditions of practical import and its susceptibility to destruction by two common disinfecting agents were examined. An indigenous strain of virus, shed to trough water at a concentration of 105 TCID50 per milliliter during an epizootic, lost 99% of its infectivity in fresh water at 4 C in 10–12 wk. There was residual infectivity after 24 wk. Survival was prolonged in sea water where loss of activity of an ATCC strain after 10 wk incubation at either 4 or 10 C was negligible. The loss in 5–6 mo was under 99%.IPN virus (107 TCID50/ml) survived drying in air at laboratory temperature and humidity for 5 but not for 6 wk. Under reduced humidity, residual infectivity was still evident after 8 wk.At a titer of 105.0 TCID50/ml, IPN virus was completely inactivated by exposure to 25 ppm available chlorine in 30 min. A concentration of 40 ppm available chlorine was required to inactivate 107.5 TCID50 of virus/ml in the same period of time. IPN virus, at a titer of 105.5 TCID50/ml, was totally destroyed by 30 ppm active iodine (Wescodyne) in 5 min. An increase in virus concentration, to 106.6 TCID50/ml increased the iodine requirement to 35 ppm to achieve the same result.The implications for salmonid culture of the persistence of IPN virus in an aqueous environment and its resistance to destructive agents are discussed.