Differences in patterns of meningoencephalitis due to bacterial kidney disease in farmed Atlantic and chinook salmon.
Tissues from 134 Atlantic salmon (Salmo salar) and 164 chinook salmon (Oncorhynchus tshawytscha), submitted to the Atlantic Veterinary College (Canada) between 1990 and 1995, were selected on the basis of their having a positive diagnosis of bacterial kidney disease (BKD), with evidence of multi-tissue infection including the brain (214 fish), or brain involvement in the absence of systemic lesions attributable to BKD (58 fish). Although meningitis was a feature of BKD in both species, encephalitis was more common in the Atlantic salmon. Specifically, a higher portion of the Atlantic salmon had encephalitis accompanying meningitis (P=0.0159), encephalitis in the absence of meningitis (P=0.0756), and brain lesions (meningitis or encephalitis) in the apparent absence of systemic lesions (P=0.0067). It is concluded that, either some aspects of the pathobiology of R. salmoninarum are dictated by the host species, or that the farm management methods used to deal with BKD are sufficiently different for the two species of salmon that they affect the pathology of the disease.