because of current concerns over the emergence of bacterial kidney disease (BKD) (Renibacterium salmoninarum) and perkinsiosis (1) in this region. Both.
CROSS-CANADA DISEASE REPORT RAPPORT DES MALADIES DIAGNOSTIQUEES AU CANADA
Eastern Canada Granulomatous nephritis associated with Rhodococcus sp. infection in Atlantic salmon (Salmo salar) The differential diagnosis of granulomatous Inephritis of commercially raised salmon in eastern Canada has recently become increasingly significant because of current concerns over the emergence of bacterial kidney disease (BKD) (Renibacterium salmoninarum) and perkinsiosis (1) in this region. Both of these diseases elicit a multisystemic, multifocal granulomatous reaction, with the kidney being a common target organ. Granulomatous nephritis in Atlantic salmon (Salmo salar) smolt from which Rhodococcus sp. has consistently been isolated (2) adds a further dimension to the differential diagnosis of this morphological condition. The following report briefly reviews the case presentation, pathology, and bacteriology of chronic nephritis of salmon associated with Rhodococcus sp. The condition was first described by Claveau (2). It involved a chronic episode of low-level mortality (approximately 0. 07 per week) affecting salmon smolt housed in 10 m diameter, plastic-lined, circular galvanized tanks, supplied with 3°C brackish water pumped from a seepage well. Affected fish had markedly enlarged kidneys which contained randomly distributed 1-4 mm round, white, soft foci with a necrotic core. Histologically, these foci were poorly encapsulated granulomas containing large numbers of Gram-positive, pleomorphic, rod-shaped bacteria. The pathogenicity of the dominant strain of bacteria (identified as Rhodococcus sp. by conventional biochemical results and gas-liquid chromatographic analysis of the cellular fatty acids) isolated from these kidneys was tested by intraperitoneal (IP) injection of Atlantic salmon smolt. When 106 and 109 bacteria
were delivered IP, a severe granulomatous peritonitis developed within three weeks. Despite this, the mortality rate was low (fewer than 1007o of fish in the groups given 109 bacteria) and morbidity was rarely apparent, although severe internal lesions developed in most of the injected fish. Based on the course of the natural disease and from the experimental challenge studies, we believe that this particular Rhodococcus sp. is pathogenic for Atlantic salmon. Although the mortality rate associated with it appears to be very low, the sub-clinical effects on production could be significant. Recognition of the potential of this Rhodococcus sp. to cause granulomatous nephritis is particularly important, because, as in BKD, the causative bacteria are Gram-positive and intracellular, and the preliminary diagnosis of BKD is often achieved using a Gram stain of an impression smear from a lesion. References 1. Cawthorn RJ, Mitchell H, Speare D. Range extension of Perkinsus (Dermocystidium) sp. (Apicomplexa) infections in farmed Atlantic salmon (Salmo salar) of eastern North America. Fish Health Sect/Am Fish Soc Newsetter 1991; 5. 2. Claveau R. Nephrite granulomatous a Rhodococcus spp. dans un elevage de saumons de l'Atlantique (Salmo salar). Med. Vt. Quebec 1991; 21: 160-161.
David J. Speare, John Brocklebank, Neil MacNair, Department of Pathology and Microbiology, Atlantic Veterinary College, Charlottetown, Prince Edward Island CIA 4P3; Robert Claveau, Laboratoire de pathologie animale, MAPAQ, Rimouski, Quecbec G5L IP4; Steve Backman, Moore-Clarke Canada, St. Andrews, New Brunswick EOG 2X0; E. Pauline Ewan, Kathryn A. Bernard, Laboratory Centre for Disease Control, Health and Welfare Canada, Ottawa, Ontario KIA OL2
Saskatchewan An outbreak of actinobacillosis in foals A pregnant mare urine farm with about 120 mares l ost 14 foals from abortions and neonatal deaths December, 1990 to late April, 1991. All aborting mares were clinically healthy. The foals were normal when born, but quickly became very weak, unable to suckle or stand, and depressed and sick. They usually died within two days of birth. Affected foals were born to mares of all ages. Other foals were born and remained healthy. The mares were fed timothy and slough hays, wheat straw, and mineral salts. Each mare was also given about 6.5 kg oats daily. Leptospiral and rhino192
pneumonitis vaccines had been given in the past three years, but not in the current year. Three 1 to 2-day-old foals were admitted to the laboratory for necropsy. They were in poor to fair bodily condition. One carcass was icteric. Septicemic lesions of various extent were present. The lungs of one foal were mottled, consolidated, and hemorrhagic. The other two foals had swollen joints filled with excessive cloudy fluid and some fibrinous exudate, and swollen kidneys containing scattered white foci. The renal capsules of one foal were strongly adherent to the Can Vet J Volume 33, Mars 1992
