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Diseases of Aquatic Organisms

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DAO 51:85-92 (2002)  -  doi:10.3354/dao051085

Relationship between antigen concentration and bacterial load in Pacific salmon with bacterial kidney disease

Owen S. Hamel*, James J. Anderson

Columbia Basin Research, School of Aquatic and Fisheries Sciences, PO Box 358218, University of Washington, Seattle, Washington 98195, USA

ABSTRACT: Using data collected to test spawning female Pacific salmon (Oncorhynchus kisutch and O. tshawytscha for the presence and severity of bacterial kidney disease (BKD), a mathematical model of the relationship between bacterial load and antigen concentration in tissues and ovarian fluid is developed. Renibacterium salmoninarum, the causative agent of BKD, secretes large amounts of a 57 kDa protein (Œp57¹), its major soluble antigen, which eventually breaks down or is otherwise removed from free circulation. Bacterial load and soluble antigen concentration in tissues are strong indicators of fish health, while in ovarian fluid they are predictors of the success of offspring. Model results indicate either an exponentially increasing antigen removal rate or an exponentially decreasing per-bacterium antigen secretion rate with increasing antigen concentration. Possible mechanisms underlying the observed relationship include a nonlinear increasing autolytic rate of the Œp57¹ antigen and a bacterium-antigen interaction threshold which prevents bacterial antigen secretion.

KEY WORDS: BKD · p57 · Mathematical model · Spawning female Pacific salmon · Bacteria · Antigen

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