Testing the ability of viral haemorrhagic septicaemia virus to evade the protective immune response induced in rainbow trout by DNA vaccination

Viral haemorrhagic septicaemia virus, a negative strand RNA virus belonging to the genus Novirhabdovirus within the family Rhabdoviridae, is the causative agent of VHS, which is a serious disease in rainbow trout and other economically important fish species. The DNA vaccine encoding the viral glycoprotein, the only surface protein of the VHSV, has been successful as an experimental prophylactic treatment against this disease, because it induces a strong innate (interferon) and adaptive (cellular and humoral) immune response. However, since RNA viruses are known to possess high variability, this work aims to evaluate whether VHSV is able to evade the protective immune response induced by the DNA vaccination. Earlier studies have demonstrated that VHSV can evade the neutralizing effect of monoclonal antibodies by mutations in the glycoprotein gene. One approach of the present study is therefore to try to isolate VHSV variants which can escape the neutralizing activity of serum from fish immunized with the DNA vaccine. To do so, a highly pathogenic VHSV isolate (DK3592B) will be repeatedly passaged in fish cell cultures in the presence of neutralizing fish serum. Another approach comprises repeated passaging of VHSV in vaccinated fish. The study was initiated recently. Current results will be presented and discussed.