Sero- and genotyping of some marine aquatic birnavirus isolates from Norway

Twelve isolates of aquatic birnaviruses (9 field isolates from marine fish and shellfish and the Ab/A(3), Sp/A(2) and N1 strains) were serotyped using an immunodot assay. The assay with 17 monoclonal antibodies revealed some serological variation among the Norwegian isolates, but the N1 strain and the Sp/A(2) type strain reacted identically. A genotyping assay based upon restriction fragment analysis of a polymerase chain reaction-amplified fragment from the VP2 coding region was run parallel to the serotyping. All the 9 serogroup A serotypes, except He/A(4) and Can. 3/A(8), were assayed in addition to the Norwegian isolates mentioned above. This method differentiated among all serotypes tested, but only small differences were observed among the Norwegian isolates. The N1 and Sp/A(2) strains reacted identically. Our results indicate homogeneity between Norwegian birnavirus isolates and support earlier studies that concluded that the N1 strain belongs to the Sp/A(2) serotype.