BKD Assays – Evaluation of the diagnostic accuracy

Principal investigator: Larry Hammell
Co-Investigators: Diana Jaramillo, Annette Boerlage, & Nicole O’Brien

Knowledge of the accuracy of diagnostic tests is essential for informed disease surveillance and control strategies. In the case of infection with the bacterium, Renibacterium salmoninarum, which causes bacterial kidney disease (BKD) in salmon, diagnosis has traditionally depended on the Immunofluorescence antibody test (IFAT). IFAT, ELISA, and PCR tests are commonly used for surveillance in apparently healthy brood fish to identify carrier fish contributing to vertical transmission. However, it is unknown whether their sensitivity and specificity are fit for the diagnosis of BKD, especially in sub-clinically affected fish. Bacterial culture, although useful and relatively inexpensive, takes up to 19 weeks to deliver results.

In this study, we assessed the diagnostic sensitivity and specificity of culture, PCR, IFAT, and ELISA tests using farmed Atlantic salmon samples sourced from populations with different health statuses and BKD prevalences. Samples were submitted to fee-for-service laboratories that routinely test for R. salmoninarum.

We calculated the characteristics of the tests on fish with clinical and subclinical BKD using Latent Class analysis (Bayesian). Further analysis of inter-laboratory reproducibility was conducted for diagnostic validation of the assays, according to OIE standards. Results will help support future epidemiological studies of BKD, with the overall goal of improved disease detection and control.