Evolution of infectious hematopoietic necrosis virus (IHNV), a fish rhabdovirus, in Europe over 20 years: implications for control.

The fish pathogenic rhabdovirus infectious hematopoietic necrosis virus (IHNV) causes substantial losses in European aquaculture. IHNV was first detected in Europe in 1987 and has since undergone considerable spread. Phylogenetic analyses of the full G-gene sequences of 73 isolates obtained from 4 countries in Europe (France, n = 18; Italy, 9; Switzerland, 4; Germany, 42) enable determination of the evolution of the virus in Europe since the first detection, and identification of characteristic changes within the G-genes of European strains. Further, the database allows us to analyse the pathways of distribution in Europe over time. The results suggest that in most of the recent cases, spread of IHNV was related to trade of infected fish. The data further demonstrate that knowledge of the sequence is required to determine the source of infections in farms.

Development of an oral vaccine for immunisation of rainbow trout (Oncorhynchus mykiss) against viral haemorrhagic septicaemia.

In the European Union Viral Haemorrhagic Septicaemia (VHS) eradication is still based on stamping out. Due to the lack of effective low cost vaccines immune prophylaxis is currently not used to combat VHS. This paper describes a new oral delivery method for immunisation of trout with attenuated virus. The vaccine consists of lyophilised virus surrounded by polyethylene glycol (PEG) and was extruded under low temperature. In the stomach of trout, the use of additional neutralising and adsorbing bases resulted in a neutral pH around the vaccine pellets, thus protecting the antigen against gastric acid. The in vivo efficacy of this delivery method was examined in three animal challenge experiments using an attenuated VHS virus (VHSV) strain as a vaccine. After vaccination, VHSV mRNA in gut, heart, kidney, spleen and blood was amplified by semi-nested PCR after RT-PCR. Indirect immune fluorescence test detected VHS vaccine virus in the gut. The expression of MHC class II, CD4 and CD8alpha mRNAs after oral vaccination was measured in gut using real-time RT-PCR. Antibody levels were measured by ELISA one week before vaccination and five weeks after vaccination. Animals were challenged six weeks after vaccination with highly virulent VHSV and mortality was recorded. The experiments showed that orally delivered vaccine virus was released from the vaccine preparation, penetrated the gut mucosa and led to higher expression levels of MHC class II and CD4 mRNAs when compared to control guts. VHSV antibodies were detected after oral vaccination. Immunisation with this new vaccine formulation was followed by a significant protection against VHSV. While the cumulative mortality in the non-vaccinated control group reached 70%, more than 75% of the orally vaccinated fish were protected upon challenge.