Survival of viral haemorrhagic septicaemia virus and infectious haematopoietic necrosis virus 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: (a) after drying on stainless steel, (b) in cell culture medium, (c) in filtered river water, (d) in unfiltered river water, and (e) survival, adsorption and desorption in river sediment and five typical soil types. The viruses survived 1 hr 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 after 1 hr. Clay soils adsorbed the least virus but had the greatest decrease in the river water inoculum (undetectable in ≤ 1 hr), 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 adsorption 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.

Survival of Frog Virus 3 in Freshwater and Sediment from an English Lake.

Ranaviruses can be transmitted by contaminated water and sediment but must retain infectivity for a sufficient period to reach and infect a susceptible host. To determine the risk a virus represents once it enters the environment, its persistence in that environment must be determined. We evaluated the survival of frog virus 3 (FV3) in water and sediment from an English lake at temperatures of 4, 15, 20, and 30 C over time. The virus survived in both water and sediment; however, survival times were significantly lower in sediment. The virus lost infectivity in both matrices with a rise in temperature. In water, time required for a 90% reduction in virus titer decreased from 34 d at 4 C to 5 d at 30 C. In sediment, required time for a 90% reduction decreased from 10 d at 4 C to 1 d at 30 C. These results can be used to estimate the persistence of FV3 in the environment and indicate that the virus could remain infectious in temperate locations for extended periods during winter.