Epidermal hyperplasias of northern pike (Esox lucius) associated with herpesvirus and C-type particles.

Northern pike from several locations in central Canada were observed to have two different types of hyperplastic epidermal lesions on the body and fins. One type of epidermal hyperplasia consisted of flat lesions, bluish-white in color with a granular or "gritty" appearance. Histological examination of this granular lesion showed the presence of grossly hypertrophied cells surrounded by normal sized epidermal cells. The enlarged nuclei in thin section contained many typical herpesvirus capsids measuring 100 nm in diameter. A large proportion of the cytoplasmic mass consisted of many dark staining inclusions in which were embedded numerous herpes-like virions. For this herpesvirus of pike the name esocid herpesvirus 1 is proposed in keeping with the herpesvirus nomenclature of Roizman et al. (19). The second type of epidermal hyperplasia was a smooth convex whitish translucent tissue mass consisting largely of a population of randomly oriented normal sized undifferentiated cells. Electron microscopic examination showed them to be associated with clusters of C-type retrovirus measuring 150 nm in diameter. The formation of these virus particles was by budding from the cytoplasmic membrane into the inter-cellular spaces. Neither the herpesvirus nor the C-type particles could be isolated in fish cell cultures.