Another problem associated with this nomenclature is that it did not take into account differences in virulence of identical isolates; a non-pathogenic isolate having an identical genetic sequence as a virulent one but differing only with two amino acids [16 ] would accordingly be excluded from list of IPNV. The purpose of the present study was to compare the mechanisms of cytopathogenesis between genetically and serologically identical and more distant isolates of aquabirnaviruses.
Source: wiktionary