Immunological Relationship of the Fish-Pathogenic OomyceteSaprolegnia parasiticato Other Oomycetes and Unrelated Fungi

Marine polyclonal antibodies produced against Saprolegnia parasitica ATCC 52719 (formerly known as S. diclina; ATCC = American Type Culture Collection), a common oomycete pathogen of fishes, recognized most S. parasitica isolates in an indirect immunofluorescence assay. However, two of the six isolates had lower titers than did S. parasitica ATCC 52719. There was considerable cross-reactivity among other taxa, which was inversely related to their taxonomic relationship to S. parasitica. Saprolegnia parasitica ATCC 52719 antigen collected from an experimentally inoculated dead fish produced the same titer as the cultured S. parasitica ATCC 52719 antigen. These findings suggest that, with further specificity refinements, these immunological assays may eventually be useful in identifying oomycete infections in clinical cases.