The use of Western blot and electroimmunotransfer blot assays to monitor bacterial kidney disease in experimentally challenged Atlantic salmon, Salmo salar L.

Abstract. Western blot (WB) and electroimmunotransfer blot (EITB) methods were used to monitor bacterial soluble antigens and scroconversion profiles, respectively, in Atlantic salmon, Salmo salar L., experimentally challenged with Renibacterium salmoninarum. The two challenged populations exhibited differences in susceptibility to R. salmoninarum permitting an evaluation of the methods in fish populations harbouring different levels of the pathogen, WB detection of R. salmoninarum soluble antigens in serum provided a sensitive method for detecting pathogen presence during the active infection stages. For comparison, results for drop-plate culture and direct fluorescent antibody techniques were obtained. During the recovery phase, surviving fish were negative for the pathogen by these methods. However, >90% of challenged fish sampled from early infection stages to the end of the experimental period (141 days post-infection) were scropositive by the EITB assay for Atlantic salmon immunoglobulin reactive with R. salmoninarum soluble antigens. The results suggest that these methods for detecting R. salmoninarum or its soluble antigens may be useful during active infections. However, asymptomatic fish populations exposed to the pathogen, perhaps having recovered from an active infection and representing potential disease carrier sources, may be more readily identified by antigen-specific antibodies using methods such as the EITB assay.