RAPID LECTIN-BASED STAINING PROCEDURE FOR THE DETECTION OF THE MYXOSPOREAN CAUSING PROLIFERATIVE KIDNEY-DISEASE IN SALMONID FISH

Lectins are proteins found initially in plants but now known from viruses, protozoans and higher animals which recognize specific glycoconjugates on cell surfaces. A rapid staining procedure using the lectin GS-1 from Griffonia simplicifolia was developed for the detection of PKX, the myxosporean causing proliferative kidney disease (PKD) in salmonid fish. A single developmental (extrasporogonic) stage of PKX could be recognized in fixed and stained kidney imprints from infected salmonids. The staining procedure involves an initial incubation of a fixed kidney imprint with 5 to 10-mu-g ml-1 of biotinylated GS-1 in phosphate buffered saline (PBS). Bound lectin is visualized by adding avidin conjugated with fluorescein (10 to 30-mu-g ml-1). The lectin-based stain removes much of the subjective evaluation required by standard Giemsa staining and fresh mount observations and is much more rapid (2 h) than standard histological procedures used for confirmatory diagnoses of PKD. The lectin stain performed equally well with PKX originating from 3 species of salmonids from France, USA, and British Columbia, Canada. The sensitivity of the procedure was not compared to histological evaluations but the lectin stain was able to detect parasites in very early stages of PKD, well before the onset of renal swelling. Although additional myxosporeans need to be tested, there was no evidence for binding of the lectin to a renal Sphaerospora sp., that does not cause PKD, found in brown trout (Salmo trutta).