Antigenic variants of infectious hematopoietic necrosis virus and implications for vaccine development

Abstract

Two monoclonal antibodies and 2 polyclonal antisera were used in cross-neutralization tests of 106 isolates of infectious hematopoietic necrosis virus (IHNV) obtained from acutely infected rainbow trout Oncorhynchus rnykiss at 4 locations in a 12 mile section of the Snake River, Idaho, USA, during 1990 to 1992. Ten antigenic groups exhibiting different neutralization profiles were identified. Approximately 91 % of these isolates fell into 3 of the groups. Each location exhibited a range of antigenic variants from 1 to 7. Prevalence of isolates within a group also varied. The frequency of different antigenic groups and prevalence of isolates within each group differed over time. Virulence comparisons using representahve isolates from 7 of the antigenic groups to challenge rainbow trout at 2 different mean body weights resulted in average cun~ulative mortalities that ranged from 14 to 92 % . Passive immunization of rainbow trout with convalescent (immune) serum from fish exposed to 1 antigenic variant provided significant protection after challenge with representative isolates from other variant groups. Relative protection of fish injected with immune serum compared to normal serum ranged from 91 to 100%. The results indicated that neutralizing activity produced against 1 antigenic variant of IHNV would cross-protect against other antigenic variants. A vaccine against a single type of lHNV may be efficacious against all IHNV strains.