Inter-Species Transmission of Viral Haemorrhagic Septicaemia Virus Between Turbot (Scophthalmus Maximus) and Rainbow Trout (Onchorhynchus Mykiss)

Viral haemorrhagic septicaemia is a serious viral disease of teleost fish with high economic impact on the aquaculture industry. The disease is caused by the viral haemorrhagic septicaemia virus (VHSV), an RNA virus belonging to the family Rhabdoviridae. Compared to other rhabdoviruses infecting fish, VHSV has an exceptional wide host range of more than 70 species across marine and aquatic environments. To establish such a wide host range host-specific adaptation would be disadvantageous, nevertheless, host-specific differences in pathogenicity have been observed for VHSV. The divergence in pathogenicity, however, is not fully resembled in the phylogeny, which indicates a correlation between geographic regions rather than host species. The objective of this study was to identify whether VHSV has the ability to transmit between different host species or whether viral transmission is restricedt to one host species through host-specific adaptation. To investigate the existence of inter-species transmission and host-specificity a cohabitation challenge between turbot and rainbow trout was conducted with turbot as donor- and rainbow trout as recipient host species. Turbot were ip challenged with a turbot- or a rainbow trout adapted VHSV isolate and subsequently grouped with naïve rainbow trout. Mortality and viral shed was monitored daily. Both virus isolates showed signs of host-specific adaptation based on differences in replication dynamics, viral production, and virulence. Host-specific adaptation, however, did not result in total restriction of inter-species transmission. Despite of host-specific adaptation, the rainbow trout adapted VHSV isolate was able to cause disease in turbot resulting in subsequent infection of cohabiting rainbow trout, thus indicating the existence of inter-species transmission of VHSV between turbot and rainbow trout.