Comparsion of selected strains of infectious hematopoietic necrosis virus (IHNV) using neutralizing trout antisera

Abstract

Antisera against representative strains of infectious hematopoietic necrosis virus (IHNV) from each of the 5 electropherotypes were prepared in rainbow trout Oncorhynchus mykiss following injections with live virus. Serum cross-neutralization comparisons by 50% plaque neutralization tests (PNT) showed low antigenic heterogeneity between the viruses, as calculated by 1/r, a measure of the antigenic relationship between 2 virus types. The only virus strain clearly different from the others 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 greater than 20, a value established as the criterion for distinguishing serotypes. The other IHNV isolates tested formed a homogeneous group sharing 1/r values of 2.1 or less. These studies provide the first evidence that rainbow trout respond distinctly with respect to the production of serum neutralizing antibodies between certain strains of IHNV. A further characterization of these responses will be important to the interpretation of epidemiological studies and the development of vaccines for the control of IHNV.