Pathogenicity trials regarding Turkish isolates of infectious pancreatic necrosis virus and viral haemorrhagic septicaemia virus in rainbow trout

Infectious pancreatic necrosis virus (IPNV) and viral haemorrhagic septicaemia virus (VHSV) are two of the major viral threats faced by the aquaculture industry in Turkey. The aim of our study was to investigate the pathogenicity of two Turkish viral strains isolated locally from the Bolu VHSV strain (Accession number: KM972678.1) and the HAH-4 IPNV strain (Accession number: KM972675). The titres of infectious virus were determined by virus titration tests using monolayer cultures of EPC cells to determine the challenge dose. The challenge trial was conducted with 40 rainbow trout (Oncorhynchus mykiss (Walbaum)) for each virus and control group. The infective dose of each virus was applied intraperitoneally as 1 x 10(7) of the tissue culture infective dose per ml. At the end of the trial period (day 21), all fish were examined for clinical signs and post-mortem changes. The average mortality rates for VHSV and IPNV were 36.6% and 33.3%, respectively. Necropsies performed on the deceased fish revealed the presence of IPNV only in fish that had been infected with IPNV, as determined using a real-time PCR method targeting the VP3 gene region of the virus. Similarly, VHSV was detected only in the fish infected with VHSV using a real-time PCR method targeting the gG gene region of the virus. In conclusion, the Bolu strain of VHSV and the HAH-4 strain of IPNV each has moderate pathogenicity in rainbow trout.