Antigenic analysis of reference strains and Norwegian field strains of aquatic birnaviruses by the use of six monoclonal antibodies produced against the infectious pancreatic necrosis virus N1 strain

Abstract. Six monoclonal antibodies (MAbs) produced against the infectious pancreatic necrosis virus (IPNV) N1 strain were used in a dot-blot assay to examine reference strains of the nine proposed serotypes and a representative selection of 81 Norwegian aquatic birnavirus isolates. These isolates had earlier been serotyped by use of a panel of 11 MAbs produced against other strains of IPNV. Correlations between the reaction patterns of the two panels of MAbs were found. All reference strains and field isolates shared two epitopes, one on VP2 and one on VP3. Seventy-seven of the field isolates reacted identically with the N1 strain (positive with all six MAbs). The Sp type strain was positive with five of the MAbs and was different from all the field strains. The other reference strains (WB, VR299, Ab, Ja, Te, He, C1, C2 and C3) were positive with two to four of the MAbs. Together with previously published data, these findings indicate that most Norwegian isolates are closely related to, or identical with, the N1 strain and belong to the Sp serotype. No correlation between the health status of Atlantic salmon and antigenicity of the isolates was found. Testing of the reference strains in ELISA revealed some discrepancies with the dot-blot results.