Morphological differentiation of virus-associated skin tumors of walleye (Stizostedion vitreum vitreum).

Abstract

Walleye populations in the central region of Canada have been observed to have at least four skin growths that are associated with different virus particles. These include lymphocystis disease, dermal sarcoma, and two different forms of dermal hyperplasia. All of these growths have been observed in walleye populations in a particular spawning run with some individual fish having more than one type of infection. Observations over a period of years indicate that these lesions can be found in the same locality from year to year although the observed incidences may vary.The histopathology and ultrastructure of lymphocystis is typical of other lymphocystis in freshwater and marine fishes consisting of grossly hypertrophied cells containing many 260 nm diameter lympho cystis virus particles.The dermal sarcoma tumors on gross observation may be confused with lymphocystis since both tumors are large, opaque, white growths often tinged with red. The dermal sarcoma can be readily differentiated on close observation by their smooth appearance in contrast to the typical granular appearance of the enlarged cells of lymphocystis.A third skin tumor identified as an epidermal hyperplasia has a clear slime-like appearance with a bluish tint and consists of cells associated with 135 nm retrovirus particles that bud from the cell membrane into the intercellular spaces. These virus particles in contrast to those of dermal sarcoma virus are fewer in number and not found within cytoplasmic vacuoles.A fourth dermal lesion, which in appearance is not unlike that of the retrovirus associated dermal hyperplasia, has a more diffuse character often with swelling of the underlying tissue. This growth is associated with a herpesvirus and is the only virus which has been routinely isolated and propagated in cell culture.

A large unintegrated retrovirus DNA species present in a dermal tumor of walleye Stizostedion vitreum

“…Retroviruses have long been suspected to b e the causative agents of some fish neoplasms (Walker 1969, Yamamoto et al 1976, Duncan 1978, Yamamoto et al 1983, 1985, Masahito et al 1988. The most convincing evidence has been provided by studies of the northern pike Esox lucius lymphosarcoma, probably the most frequent malignant neoplasm found in wild vertebrates (Sonstegard 1976).…”

Spontaneously productive C-type retrovirus infection of fish cell lines

“…Similar viruses have not hitherto been reported in fish cell cultures, but C-type particles have been observed in lesions from epidermal hyperplasia of northern pike (Esox lucius) (Winqvist et al, 1968;Yamamoto et al, 1983), epidermal hyperplasia and dermal sarcoma of walleye perch (Stizostedion vitreum) (Walker, 1969;Yamamoto et al, 1985), swimbladder fibrosarcoma of Atlantic salmon (Salmo salar) (Duncan, 1978) and fin papillomatosis of European smelt (Osmerus eperlanus) (Anders, 1989). C-type particles and reverse transcriptase activity associated with 1.15 to 1.16 g/ml sucrose gradient fractions have also been identified in tissue from northern pike lymphosarcoma (Papas et al, 1976) and white sucker (Catostomus commersoni) papillomatosis (Sonstegard, 1977).…”

Walleye Dermal Sarcoma Virus Retroviral Cyclin Directly Contacts TAF9

“…Walleye dermal sarcoma virus (WDSV), a member of the epsilonretroviruses in the family Retroviridae, is a complex retrovirus etiologically associated with dermal sarcomas in walleye fish (Sander vitreus, formerly Stizostedion vitreum) (13,14,(26)(27)(28). The seasonal appearance of this disease is characterized by the expression of low levels of spliced accessory gene transcripts A1 and B during the period of tumor development and high levels of full-length and spliced transcripts during tumor regression (17,20).…”