Mortality of rainbow trout and sockeye salmon exposed to 16 genotypes of infectious hematopoietic necrosis virus (Genogroups U, M) at two doses and two temperatures

In this study, we demonstrate that infectious hematopoietic necrosis virus (IHNV), which made a host jump from sockeye salmon (Oncorhynchus nerka) to rainbow trout (O. mykiss), has not conformed to classical pathogen evolution theory. We quantified virulence in the endemic and novel hosts using common garden in vivo experiments with 16 archival IHNV isolates collected from 1972-2017, which span the period from shortly after the host jump and the subsequent 45 years of host adaptation. These virus isolates also represent two distinct phylogenetic genogroup, each associated with either the endemic or novel host. The experiments were replicated across two research facilities, two challenges dosages, and two temperatures.