COMPARISON OF SELECTED STRAINS OF INFECTIOUS HEMATOPOIETIC NECROSIS VIRUS (IHNV) USING NEUTRALIZING TROUT ANTISERA

Antisera against representative strains of infectious hematopoietic ne crosis virus (IHNV) from each of the 5 electropherotypes were prepared in rainbow trout Oncorhynchus mykiss following injections with live v irus. Serum cross-neutralization comparisons by 50% plaque neutralizat ion tests (PNT) showed low antigenic heterogeneity between the viruses , as calculated by 1/r, a measure of the antigenic relationship betwee n 2 virus types. The only virus strain clearly different from the othe rs was the representative electropherotype 2 isolate (CST-82), with 1/ r values from 5.2 to 15.6 when compared to the other isolates. The 1/r values obtained for the type 2 IHNV isolate were, however, not greate r than 20, a value established as the criterion for distinguishing ser otypes. The other IHNV isolates tested formed a homogeneous group shar ing 1/r values of 2.1 or less. These studies provide the first evidenc e that rainbow trout respond distinctly with respect to the production of serum neutralizing antibodies between certain strains of IHNV. A f urther characterization of these responses will be important to the in terpretation of epidemiological studies and the development of vaccine s for the control of IHNV.