Viral haemorrhagic septicaemia virus multiplication and interferon production in rainbow trout and in rainbow trout × brook trout hybrids

Rainbow trout ( Oncorhynchus mykiss) susceptible to Viral Haemorrhagic Septicaemia (VHS) Virus type 1 and rainbow trout × brook trout ( Salvelinus fontinalis) triploid hybrids were challenged with VHSV by either immersion or i.p. injection of the virus. In both cases susceptible rainbow trout displayed an increasing viraemia which was paralleled by high interferon titres in the serum. In contrast virus multiplication as well as serum interferon production remained low in resistant hybrids. When blood leucocytes were infected in vitro the adsorption of virus appeared low and there was no obvious multiplication of the virus and trout and hybrid leucocytes released similar levels of interferon in the culture medium. When leucocytes were stimulated by monolayers of VHSV infected cells fixed with glutarldehyde at the time virus was budding at their surface, interferon production was the same in kidney leucocytes but was much lower in hybrid than in trout blood leucocyte cultures.