Characterization of IHNV isolates associated with neurotropism.

Rainbow trout with a 'neurotropic' form of infectious hematopoietic necrosis (IHN) exhibited behavioral abnormalities and had high virus concentrations localized in brain tissue. Fish with 'hematopoietic' IHN exhibited typical disease signs with the highest concentrations of virus detected in kidney-spleen tissue. Infectious hematopoietic necrosis virus (IHNV) isolates obtained from brain or kidney-spleen tissue were tested for serological relatedness and virulence and pathogenicity differences in 2 sizes of rainbow trout. No major differences were detected by indirect fluorescence tests. Serum neutralization profiles showed 2 predominant patterns that differed dependent upon tissue of origin. However, virulence and pathogenicity differences were not evident.