Plasmacytoid leukemia of chinook salmon.

Plasmacytoid leukemia is a common disease of seawater pen-reared chinook salmon (Oncorhynchus tshawytscha) in British Columbia, Canada, but has also been detected in wild salmon, in freshwater-reared salmon in United States, and in salmon from netpens in Chile. The disease can be transmitted under laboratory conditions, and is associated with a retrovirus, the salmon leukemia virus. However, the proliferating plasmablasts are often infected with the microsporean Enterocytozoon salmonis, which may be an important co-factor in the disease.

Preliminary analysis of the polypeptides of the salmon leukemia virus (SLV) and evidence for development of a bimodal viremia following SLV infection.

A retrovirus, known as salmon leukemia virus (SLV), was purified from farm-reared chinook salmon (Oncorhynchus tshawytscha) with plasmacytoid leukemia (PL). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of purified SLV revealed the presence of 9 virus-associated polypeptides with molecular weights from 82 kDa to 15 kDa. Endoglycosidase digestion and alcian blue staining of viral polypeptides separated by SDS-PAGE, and immunoprecipitation experiments using hyperimmune antisera suggest that the non-glycosylated 27 kDa polypeptide may represent a capsid-associated protein and the 82 kDa glycoprotein may represent an envelope-associated protein, which appears to be composed of a 67 kDa protein moiety. Fish injected with PL-positive tissue homgenate developed a bimodal viremia, as indicated by the presence of cell-free, virus-associated reverse transcriptase activity and SLV in serum of fish from 1 to 3 wk post-injection and again from 7 wk on through the rest of the study. If horizontal transmission of SLV and PL occurs in infected chinook salmon, it is most likely to occur after the second viremic period begins.

Isolation of a retrovirus from two fish cell lines developed from chinook salmon (Oncorhynchus tshawytscha) with plasmacytoid leukaemia.

Two new cell lines developed from chinook salmon with plasmacytoid leukaemia have been found to be producing a virus. The virus has been identified as a retrovirus based on: type of c.p.e. induced in culture; morphology and density of the particle; presence of Mn(2+)-dependent, poly(rA)-directed reverse transcriptase activity which was associated with a density of 1.16 to 1.18 g/ml in sucrose; electrophoretic pattern of the polypeptides from purified virions; elevated [3H]UTP labelling of RNA in the cell cultures occurring at a density of 1.16 to 1.18 g/ml in sucrose. This report describes the first isolation of a retrovirus from a salmonid cell line.

A retrovirus in chinook salmon (Oncorhynchus tshawytscha) with plasmacytoid leukemia and evidence for the etiology of the disease.

A plasmacytoid leukemia (PL) has caused mortalities in chinook salmon (Oncorhynchus tshawytscha) reared in seawater netpens in western British Columbia, Canada, since 1988. Kidney or eye tissues from 11 of 13 fish from netpens with clinical PL had reverse transcriptase (RT) activity. This RT activity was associated with virus particles of retrovirus morphology and buoyant density. In a transmission experiment, PL-positive donor fish tissues also had RT activity and virus particles of retrovirus morphology and buoyant density, as did recipient fish tissues following development of the disease 6 weeks postinjection with a tissue homogenate from the donor fish. Kidney and spleen tissues from fish that developed PL following injection with an inoculum that was passed through a 0.22-micron filter, in a separate experiment (M. L. Kent and S. C. Dawe. Further evidence for a viral etiology in the plasmacytoid leukemia of chinook salmon Oncorhynchus tshawytscha. Dis. Aquat. Org., in press, 1992), also exhibited RT activity. The virus particles observed by electron-microscopic examination of tissues or sucrose fractions from PL-positive fish were enveloped and were about 110-nm diameter with a central electron-dense core. Polypeptides of about M(r) 120,000, 80,000, 42,000, 27,000, 25,000, 22,000, and 19,000 were observed when purified virus particles were examined by polyacrylamide gel electrophoresis analysis. Many infectious neoplasms of animals, including fishes, are caused by retroviruses. The evidence in this study shows the presence of a retrovirus in chinook salmon with PL and further suggests a retroviral etiology of the disease. We are tentatively calling this virus salmon leukemia virus.

Preliminary results on the seasonality and life cycle of the parasitic dinoflagellate causing bitter crab disease in Alaskan tanner crabs (Chionoecetes bairdi).

Tanner crabs (Chionoecetes bairdi) from the Sullivan Island area of southeast Alaska were sampled for 1 year to determine the prevalence and intensity of the parasitic dinoflagellate which causes bitter crab disease (BCD). The prevalence and intensity of infection were the greatest in the summer, declined in the fall and winter, and increased again in the spring. A possible relationship between softer, newer shells and higher levels of parasitism was also observed. In vivo transmission studies in the laboratory suggested there are several morphologically different forms of the vegetative cell of the BCD dinoflagellate which occur prior to sporulation of the parasite. In addition, it appears that both the two spore types produced by the parasite are infectious by injection and that there is no ploidy difference between the two spore types and the vegetative cell, suggesting that the two spore types may not represent separate sexes.

Coccidia, X-cell pseudotumors and Ichthyophonus sp. infections in walleye pollock (Theregra chalcogramma) from Auke Bay, Alaska.

One hundred twenty-five walleye pollock (Theragra chalcogramma) were collected from Auke Bay, Alaska (USA) in 1985 and examined for histologic evidence of disease-causing infectious agents in 1987. A Goussia sp.-like coccidium was found in the kidney tubules of 75% and an Eimeria sp.-like coccidium was found in the intestine of 18% of the fish examined. The kidney coccidium was associated with sloughing of the tubular epithelium, peritubular fibrosis and granuloma formation. The intestinal coccidium was associated with severe tissue displacement and inflammation. In addition, X-cell pseudotumors were observed in the pseudobranchs (4%), and the fungus Ichthyophonus sp. was observed in the kidney, intestine or brain of 2% of the pollock.