Principles underlying the epizootiology of viral hemorrhagic septicemia in Pacific herring and other fishes throughout the North Pacific Ocean

Abstract

Although viral hemorrhagic septicemia virus (VHSV) typically occurs at low prevalence and intensity in natural populations of Pacific herring (Clupea pallasii) and other marine fishes in the Northeast Pacific Ocean, epizootics of the resulting disease (VHS) periodically occur, often in association with observed fish kills. Here we identify a list of principles, based on a combination of field studies, controlled laboratory experiments, and previously unpublished observations, that govern the epizootiology of VHS in Pacific herring. A thorough understanding of these principles provides the basis for identifying risk factors that predispose certain marine fish populations to VHS epizootics, including the lack of population resistance, presence of chronic viral carriers in a population, copious viral shedding by infected individuals, cool water temperatures, limited water circulation patterns, and gregarious host behavioral patterns. Further, these principles are used to define the epizootiological stages of the disease in Pacific herring, including the susceptible (where susceptible individuals predominate a school or subpopulation), enzootic (where infection prevalence and intensity are often below the limits of reasonable laboratory detection), disease amplification (where infection prevalence and intensity increase rapidly), outbreak (often accompanied by host mortalities with high virus loads and active shedding), recovery (in which the mortality rate and virus load decline owing to an active host immune response), and refractory stages (characterized by little or no susceptibility and where viral clearance occurs in most VHS survivors). In addition to providing a foundation for quantitatively assessing the potential risks of future VHS epizootics in Pacific herring, these principles provide insights into the epizootiology of VHS in other fish communities where susceptible species exist.Résumé : Si le virus de la septicémie hémorragique virale (VSHV) est typiquement présent à faible prévalence et intensité dans les populations naturelles de hareng du Pacifique (Clupea pallasii) et d'autres poissons marins dans le nord-est de l'océan Pacifique, des épizooties de la maladie en découlant (SHV) se produisent périodiquement, souvent associées à des mortalités de poissons observées. Nous présentons une liste de principes, reposant sur une combinaison d'études de terrain, d'essais contrôlés en laboratoire et d'observations non publiées, qui régissent l'épizootiologie de la SHV chez le hareng du Pacifique. Une compréhen-sion exhaustive de ces principes fournit les bases qui permettent de cerner les facteurs de risque prédisposant certaines populations de poissons marins aux épizooties de SHV, dont l'absence de résistance de la population, la présence de porteurs viraux chroniques dans une population, l'élimination copieuse du virus par des individus infectés, de faibles températures de l'eau, une circulation de l'eau limitée et des comportements grégaires des hôtes. Ces principes sont en outre utilisés pour ...

The Nucleoprotein and Phosphoprotein Are Major Determinants of the Virulence of Viral Hemorrhagic Septicemia Virus in Rainbow Trout

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Review of infectious agent occurrence in wild salmonids in British Columbia, Canada

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