Comparison of the enzyme-linked immunosorbent assay (ELISA) and the fluorescent antibody test (FAT) for measuring the prevalences and levels of Renibacterium salmoninarum in wild and hatchery stocks of salmonid fishes in Alaska. USA

Abstract

ABSTRACT. The enzyme-linked immunosorbent assay (ELISA) and the fluorescent antibody test (FAT) were compared for their sensitivity in detection of Renibacterjum salmoninarum (Rs) in kidney tissues of Alaskan salmonids. The ELISA appeared to be more sensitive in detecting Rs infections. The FAT did not detect Rs in 80 % of the ELISA-positive samples but was positive for Rs in 28 'K, of the samples that were ELISA-negative. This contradiction may have been due to low-level washover of Rs cells from smears containing large numbers of Rs cells when slldes containing nlultiple samples were rinsed in d common vessel during the FAT procedures. The FAT routinely did not detect infections in Rs-positive fish the tissues of which produced a mean ELISA optical density value 50.173, and inconsistently detected infections in fish with ELISA values > 0.173 but < 0.978. The 0.978 optical density was the mean ELISA value at which the FAT routinely detected Rs-positive fish. Based on the ELlSA results, Rs occurred in only 9 % of the Alaskan Pacific salmon tested in both wild (85 "/U) and hatchery (81 %) stocks. The very high stock prevalences and levels of Rs antigen detected in wild trout Oncorhynch~~s spp., char Salvelinus spp., and grayling Thymallus arcticus having no clinical signs of bacterial kidney disease suggest these species may be somewhat resistant hosts and important freshwater reservoirs of Rs.

Different prevalences of Renibacterium salmoninarum detected by ELISA in Alaskan chinook salmon Oncorhynchus tshawytscha spawned from freshwater and seawater

“…This observation was consistent with current hatchery operations in which the greatest fish Typical Rs cells were detected by FAT in the kidney tissues from fish in I seawater and freshwater when corresponding ELISA OD values were 11.0 (Meyers et al 1993a). No crossreacting bacteria were observed by the FAT in kidney tissues or water samples that could potentially have confounded the ELISA results.…”

“…Kidney samples producing ELISA optical density (OD) values 20.095 were considered positive for the Rs antigen. Ktdney tissues having hlgher ELISA OD values approaching 1.0 were examined by the indirect and the drect fluorescent antibody tests (FAT) to confirm the presence of the Rs organism (Meyers et al 1993a). The direct FAT used the same anti-Rs antiserum as the ELISA, but the antiserum was conjugated with fluorescein isothiocyanate instead of horseradish peroxidase.…”

Association of viral hemorrhagic septicemia virus with epizootic hemorrhages of the skin in Pacific herring Clupea harengus pallasi from Prince William Sound and Kodiak Island, Alaska, USA

“…A direct fluorescent antibody test (FAT) for Renibacterium salmoninarum was also performed on kidney smears from the Graveyard Point herring using methods described by Meyers et al (1993).…”

Mortality and kidney histopathology of chinook salmon Oncorhynchus tshawytscha exposed to virulent and attenuated Renibacterium salmoninarum strains

“…Low numbers of R. salmoninarum (from 1 to 5 or 6 to 50) in kidney smears tested by FAT have previously been shown to be ELISA-negative in a study which compared the 2 detection methods (Meyers et al 1993). Consequently, low numbers of R. salmoninarum detected by FAT may not represent high infection levels or clinically diseased fish.…”