THE ROUTE OF ENTRY AND PROGRESSION OF INFECTIOUS HEMATOPOIETIC NECROSIS VIRUS IN ONCORHYNCHUS-MYKISS (WALBAUM) - A SEQUENTIAL IMMUNOHISTOCHEMICAL STUDY

Steelhead trout, Oncorhynchus mykiss (Walbaum), fry were experimentall y infected with infectious haematopoietic necrosis virus (IHNV) Round Butte 1983 (Type 1). Fry were sampled daily, before and during the epi zootic. Fish tissues were tested for infectious virus by tissue cultur e assay and for IHNV nucleocapsid protein by alkaline phosphatase immu nohistochemistry (APIH). The progression of virus through the tissues was followed by APIH until the fourteenth day. Viral infection progres sed from two major sites: from the gills into the circulatory system; and from the oral region into the gastrointestinal tract and then into the circulatory system. Once in the blood, virus was disseminated to virtually every organ. Progression of IHNV within and between organs i s discussed.