Parallel phylogenetic analyses using the N, G or Nv gene from a fixed group of VHSV isolates reveal the same overall genetic typing

Different genetic regions representing the viral phospho-(P), nucleocapsid-(N) or glyco-protein (G) gene have been used for phylogenetic studies of viral haemorrhagic septicaemia virus (VHSV). Since these analyses were performed on different virus isolates using various genomic regions, it has been difficult to evaluate how the choice of target region affects the output of the analyses.

To address this, we sequenced and performed parallel phylogenetic analysis of an N gene fragment, the entire Nv (non-structural protein) and G genes, and 4 different fragments of the G gene from a fixed virus panel. The overall genotyping of the selected isolates was identical for the 7 target regions, but separation of Genotype I sub-lineages was best when the analysis was performed on the full length G gene (1524 nucleotides, nt).

Good resolution was furthermore obtained using smaller sequencing windows represented by a G gene fragment (nt 360 to 720) or the Nv gene (366 nt), although these regions had different characteristics with respect to resolution of Genotype I sublineages and resolution within Sub-lineage Ia. Phylogenetic analysis based on the deduced amino acid sequences was also performed.

The phylogenetic relationship between the nucleotide and amino acid sequences of the isolates corresponded best in the case of the N gene/protein. For the 6 other genomic regions, genetically distant isolates occasionally grouped together when compared at protein levels. No clear relationship between the G gene genotyping and serotyping with neutralising (G protein specific) antibodies was observed, stressing that epidemiological analysis based on phenotypic characteristics such as serotype could be misleading.