Akademik Veri Yönetim Sistemi
22nd International Conference on Diseases of Fish and Shellfish, Heraklion, Yunanistan, 1 - 04 Eylül 2025, cilt.1, sa.1, ss.1, (Özet Bildiri)
Marker Candidates and
Reverse Genetic Approaches in Viral Hemorrhagic Septicemia Virus Ie Genotype
Introduction: Viral hemorrhagic septicemia virus (VHSV) is a rhabdovirus which
also causes severe disease in several salmonid species. The disease has been
found in all age groups of susceptible fish, with mortality rates reaching 80%
to 100%, particularly in fry and fingerlings. It has presented serious problems
to rainbow trout culture in Europe for over 60 years. The phylogenetic studies
undertaken so far have identified four genotypes over the Northern Hemisphere
(I, II, III, and IV) encompassing ten subtypes (Ia, Ib, Ic, Id, Ie, If IVa,
IVb, IVc, IVd) and many clades. The Ia genotype, which is associated with high
mortality in trout and salmon in the European continent, is widespread.
However, only the Ie subgenotype has been reported in Türkiye so far. It is
known that in determining virulence in VHS isolates from these genotypes, the N
gene is primarily effective, followed by the P gene. However, although some
articles report that the G, Nv and L genes do not significantly affect
virulence, there are also reports to the contrary. There are limited studies on
the virulence of Ie genotypes.
Methodology: In this study, the Bolu-2006 isolate, which caused
over 80% mortality and significant economic losses in rainbow trout cultured in
freshwater in Türkiye in 2006, was used. Serial passages of the virus were
performed in EPC cell culture. After serial passages, pathogenicity tests were
performed with the virus. Following this process, a complete gene analysis of
the virus was obtained using the NGS method.
Results and Conclusions: In this study, striking differences were observed in
the Sanger and NGS sequence data of the isolate belonging to the Ie genotype.
While no changes were found in any gene, only a five nt change was detected on
the G gene (3866A-G; 4251T-C, 4429T-C; 4438T-C; 4446T-C). These changes caused
three amino acid changes (303N-D; 431L-P; 496I-T). The data reflected in the
mortality rate showed that while the virus was adapted to cell cultures
originating from different species, there were also changes in its virulence.
The mortality rate decreased from 80% to 30.6%. It is thought that it can be
shown as a virulence marker candidate in the Ie subgenotype when compared with
the changes and retrospective virulence studies. The next part of the study
will investigate the effect of 5 nt on virulence, single and multiple, using
the reverse genetic method.