Practical Approach to Infectious Pancreatic Necrosis Virus (IPNV) Disinfection Using Gaseous Formaldehyde

Abstract

Infectious pancreatic necrosis virus (IPNV) was isolated from rainbow trout, Onchorhynchus mykiss, brook trout, Salvelinus fontinalis, and brown trout, Salmo trutta, at two fish culture facilities in Alberta, Canada. In 1989, a large-scale fumigation with formaldehyde gas was used to eliminate the virus from the buildings and equipment at Sam Livingston Fish Hatchery, Calgary and Raven Brood Station, Caroline. The sealed fumigation area was first pressure tested. Then, two open 200-L metal barrels, distanced from any flammable material, were placed inside the fumigation area. Each contained enough potassium permanganate for the fumigation. A metering pump was positioned outside the fumigator and connected through a valve to a container of water and one of formalin. Plastic tubing delivered the liquid to the barrels, which each contained a temperature sensor. The speed of the formalin delivery was regulated so that the reaction in the barrel containing the permanganate could be kept at a temperature of approximately 119°C. A variable speed metering pump delivered measured doses of formalin and permanganate: to 26.5 g of crystalline potassium permanganate, 53 mL of a 37% solution of formalin (CH₂0) was added for each cubic meter fumigated. To avoid damage to the plastic tubing from heat, a metal tip was attached to the portion of tubing inserted into each barrel. The largest space fumigated by this procedure was 1,088.5 m³, for which 60 L of formalin was pumped in about an hour into a barrel containing 30 kg of permanganate. If the reaction overheated-too much formalin was pumped in over a given time-the metering pump was stopped. If the heat inflamed the potassium permanganate in the barrel, water was delivered through the metering pump by switching the valve. After the premises were assessed to be free from any damage, the valve was switched to the other barrel and the fumigation continued. To achieve disinfection, formaldehyde gas was held at >10 g/mL for 8 hours within the fumigation area, then neutralized by bubbling through water containing potassium permanganate. The fish stocks were regularly checked according to Canadian health regulations for diseases. Five years after the fumigation, the disinfected hatcheries have had no recurrence of IPNV.