An experimental study of the susceptibility of Atlantic salmon fry, Salmo salar L., to viral haemorrhagic septicaemia

Abstract. Infection trials using two serotypes of VHS viruses (type 1 and 23/75) demonstrated that Atlantic salmon fry were susceptible to the disease when injected intraperitoneally (i.p.) with 10³ pfu of virus/fish but resistant to infection by a bath method when exposed for 3 h in water containing 5 × 10⁴ pfu of virus/ml. In the i.p.-infected fish, mortality reached 78 and 67% within 13 days with VHSV₁ nad 23/75 serotypes, respectively. High virus yields were recovered from infected fish and virus shedding was demonstrated by the onset of VHS in rainbow trout kept in the outflow water from the aquaria containing infected salmon. Neither mortality nor virus shedding occurred in salmon infected by the water route but virus multiplication was demonstrated in 2 of 60 fish with VHSV₁ and 3 of 60 fish with virus 23/75. On day 79 post-infection the sera from surviving salmon of both i.p. and bath infection trials exhibited good neutralizing titres (around 1000) against the homologous viruses.