Virus diseases of the salmonidae in the western United States. I. Etiology and epizootiology

The history of fish diseases in western United States shows an increasing awareness that viruses could cause epizootics in fish. Fishery biologists bunked first, for protozoan and metazoan parasites, then for bacteria, and if none could be identified assumed that the mortalities were attributable to nutritional deficiency, Microbiologists in general were cognizant of virus diseases in other animals and investigators of fish diseases were alert to the possibility that piscine epizootics could be of similar cause. In 1950 an epizootic occurred in sockeye salmon (Gncorhynchus norkm) that was shown to have a viral etiologic agent.

In recent years, with increasing frequency, we have been able to demonstrate a virus utiology for epizootics and panzootics in trout and salmon in several states in the West.  FIGURE 1 is a map showing the location of epizootics of infectious pancreatic necrosis (IPN), Sacramento River chinook disease (SRCD), Oregon sockeye disease (OSD), and Columbia River sockeye disease (CRSDJ. The pathology and immunopathology of these are discussed in detail in other reports. The present report was initiated as a review of the literature concerning the diseases and to present in brief a description of their etiologic agents.