Quantitative analysis of the fusion activity of different variants of Infectious Salmon Anaemia Virus (ISAV).

Infectious Salmon Anaemia (ISA) is a viral disease that was first recorded in Norwegian juvenile Atlantic salmon (Salmo salar) in 1984 and has since been reported in all the major salmon producing nations, including North America, Scotland, the Faroe Isla nds and Chile. Despite a good management of the disease in Norway and its eradication in Scotland, ISAV still remains one of the most serious viral diseases of farmed Atlantic salmon which can result in significant economic loss. Previous work has highl ighted evidence for the existence of a variant of ISA virus in both the Norwegian and Scottish coastal environment and in marine Atlantic salmon farms. This variant is characterised by a longer segment 6 in a highly polymorphic region (HPR) encoding for a 35 aa stretch of the ISAV HE, located in the ectodomain of the protein stalk close to the transmembrane region. This atypical ISAV segment 6 gene sequence, the longest discovered to date and often referred to as the full-length HPR or HPR0, does not app ear to cause disease in Atlantic salmon. However, All currently characterised virulent isolates from ISA outbreaks have HPR shorter than HPR0 which strongly indicates variation in this region is important for virulence (Mjaaland et al., 2002). This has led to the hypothesis that the sequence diversity observed with virulent strains may have arise from deletion events from this full length precursor gene, which would act as a viral reservoir and generate more or less pathogenic virus strains. This 6 we eks project will aim at investigating the effect of the HPR0 segment 6 on the fusion activity of the virus and comparing the fusion ability of the avirulent HPR0 with the virulent HPR ISAV strains by using an in vitro expression systems based on fish cell s.