Survival of viral haemorrhagic septicaemia virus (VHSV) and infectious haematopoietic necrosis virus (IHNV) in the environment and dried on stainless steel.

Viral haemorrhagic septicaemia virus (VHSV) and infectious haematopoietic necrosis virus (IHNV) are important viral pathogens posing a serious threat to salmonid fish. Survival of two isolates of IHNV and one of VHSV was assessed at temperatures ranging from 4 to 25°C: (i) after drying on stainless steel, (ii) in cell culture medium, (iii) in filtered river water (iv) in unfiltered river water, and (v) survival, adsorption and desorption in river sediment and five typical soil types. The viruses survived 1 hour to >84 days depending on the conditions. Survival was inversely related to temperature and organic and inorganic content. Both viruses remained infectious after being dried on stainless steel for several weeks highlighting the risk of mechanical transmission and persistence in a dry environment. Both adsorbed to the soils from the river water inoculum, with titres between 5.56x104 and 2.58x108 TCID50 ml-1 after 1 hour. Clay soils adsorbed the least virus but had the greatest decrease in the river water inoculum (undetectable in ≤1 hour) and there was no desorption. Virus desorbed from the other soils into the surrounding water at different rates dependant on soil type, (longest desorption was from chalk loam and sandy soil - detected at 28 days). When desorption was no longer detectable, virus persisted, adsorbed to the soil, and remained infectious (the longest adsorbance was detected in clay loam for ≥49 days, but all the viruses adsorbed to soils were likely to have survived longer than that detected, based on their rate of decay). The long survival of the viruses, particularly at cooler temperatures, highlights the risk of survival in the environment and waterborne spread. The data presented here are highly relevant for assessing risk of pathogen introduction via fomites (stainless steel) and for deciding on best control measures in the context of disease outbreaks.