Viral hemorrhagic septicemia (VHS) is an emerging disease posing a threat to the European rainbow trout industry. In Poland VHS is diagnosed in every fifth rainbow trout farm. Glycoprotein encoded by gene G of VHSV facilitates virus entrance into the cell and is an important antigen responsible for neutralizing antibody production. Based on sequence analysis of this gene 4 major genotypes of VHSV, with many different sub-groups, have been established. To analyze several Polish strains of VHSV we applied one step RT-PCR and semi-nested PCR for detecting and sequencing the gene encoding variable fragment of virus glycoprotein. We tested 28 samples of spleen and liver from rainbow trout of various sizes (70-300 g). The fish originated from 10 different farms in North-west Poland. Ten virus strains from 3 different rainbow trout farms were isolated in EPC. They were subsequently proved to be VHSV by means of the RT-PCR method. Semi-nested PCR appeared to be more sensitive, since 12 samples out of 28 were identified as being VHSV positive, whereas only 6 samples were positive using RT-PCR. Sequences of gene encoding variable glycoprotein fragments (320 bp) of 5 randomly chosen Polish VHSV strains appeared to be identical, indicating the common origin of VHS outbreaks in all examined rainbow trout farms. Phylogenetic analysis was performed using sequences of one representative Polish VHSV strain and sequences of 22 strains belonging to 4 different genotypes as was previously published. In accordance with earlier results all the VHSV strains sequences were clustered in 4 genotypes. Polish VHSV strain clustered in genotype Ia as did other continental strains of VHSV.
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