Haemorrhagic kidney syndrome of Atlantic salmon, Salmo salar L.

This report describes a new syndrome affecting farmed Atlantic salmon on th e Canadian east coast that has resulted in increased morbidity and mortalit y in affected stocks. The major pathological findings are apparent only mic roscopically and include renal interstitial haemorrhage and acute tubular n ecrosis and tubular casting. As a result, the disease has become known as h aemorrhagic kidney syndrome (HKS). Affected fish are lethargic and anorecti c, and lark external lesions. Clinically, HKS fish are anaemic, hypoprotein aemic and hyperosmolalic, with increased serum concentrations of sodium and chloride. At necropsy, internal changes ranged from apparently normal to i nclude one or several of the following: swelling and/or patchy reddening of the kidney, pale gills, exophthalmos, serosanguinous ascites, darkening of the posterior intestine and splenomegaly. Ultrastructurally, viral inclusi ons were found in the cytoplasm of erythrocytes of HKS fish, and there were unusual electron-dense inclusions within the tips of renal tubular microvi lli of HKS fish. The significance and relevance of the ultrastructural find ings to HKS are unknown. Virus isolation was attempted using CHSE, RTG-2, F H-10, BE and EPC cell lines; no virus was isolated. Bacteriological analysi s failed to reveal significant pathogens. Analysis of tissues for heavy met als and pesticides was negative. Assays for clostridial toxins, lipopolysac charide and verotoxins were negative. The aetiology of HKS remains unresolv ed.