Eighteen years of vaccination against viral haemorrhagic septicaemia in France.

Viral haemorrhagic septicaemia (VHS) has been considered for many years to be a major cause of loss in the French trout industry. The high prevalence of VHS in certain geographic areas made a control strategy based on control policy unfeasible. This provided the impetus for immunoprophylaxis development that resulted in 3 successive types of vaccines: inactivated, live attenuated and recombinant vaccines. When delivered by intraperitoneal injection, the 2 propiolactone-inactivated VHS virus was immunogenic and/or protective for trout all of sizes, but it was not suitable for the practical immunization of alevin, the trout life stage that is the most sensitive to VHS. A carp cell-passed, attenuated variant of the VHS virus was effective after both immersion or injection delivery and met the practical requirements of juvenile vaccination. However, this vaccine was discarded because it retained some virulence that discouraged the launching of its commercialization. Then came the era of genetically engineered vaccines. The recombinant glycoprotein of VHSV produced in Escherichia coli or in Saccharomyces cerevisiae failed to protect fish whatever the route of delivery. A recombinant baculovirus vaccine was found to be immunogenic and protective against VHS, but only when delivered by injection. Due to its cost and route of delivery, the latter vaccine was not licensed. Simultaneously, the sudden occurrence of another rhabdovirosis, infectious haematopoietic necrosis (IHN), in France, rendered vaccination against VHS questionable. Indeed, no cross-protection between these 2 rhabdoviroses exists. If vaccination is still believed to be an effective control method for VHS, it should be based in the future upon an autoreplicative vaccine.(ABSTRACT TRUNCATED AT 250 WORDS)