Search

Bacterial kidney disease (BKD) diagnosis is often carried out by IFAT, ELISA, and PCR because these tests yield rapid results compared with bacterial culture for the causative agent, Renibacterium salmoninarum . However, the diagnostic sensitivity (DSe) and specificity (DSp) of these tests is generally unknown, particularly in subclinically infected Atlantic salmon. Bayesian models were used to analyse test results from 454 field samples sourced from salmon populations with different infection status and submitted to independent laboratories. Results showed that DSe was highly dependent on the presentation of infection. When applied to fish with BKD-associated gross lesions, the highest to lowest posterior medians for DSe were: PCR2 (0.98), PCR1 (0.97), bacterial culture (0.86), ELISA (0.82) and IFAT (0.75). When applied to fish without lesions, the posterior medians for DSe were: PCR1 (0.82), PCR2 (0.82), bacterial culture (0.29), IFAT (0.29) and ELISA (0.21). The posterior medians for DSp were similar in populations with and without lesions. ELISA had the highest DSp (0.99), followed by culture (0.98–0.99), IFAT (0.96), PCR1 (0.94–0.96) and PCR2 (0.83–0.84), where different numbers reflect the estimates for populations with or without lesions respectively. Among tests that were evaluated for intra-laboratory repeatability (ELISA, PCR1 and IFAT), ELISA had the highest repeatability (kappa = 0.82). We concluded that PCR tests were the fittest of the evaluated tests for the purpose of screening subclinically-infected adult Atlantic salmon. [ABSTRACT FROM AUTHOR]

Abstract: The movement of live fish between fish farms has been identified as a critical risk factor in the spread of disease yet these movements are an essential part of fish farm production cycles. Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum, is a disease which affects farmed salmon and trout production, although the impact on trout is considered less serious than on salmon. It is therefore desirable to minimise the exposure of salmon to R. salmoninarum. The approach presented here shows the potential for the salmon and trout industries to be split into two separately managed compartments in terms of control of spread of BKD by live fish movements. This compartmentalisation system is supported by the low number of cross compartment movements with only six out of 207 active farms in compartment S (mainly salmon) receiving fish from a farm located in compartment T (mainly trout). [Copyright &y& Elsevier]

Abstract: Bacterial kidney disease (BKD) (caused by Renibacterium salmoninarum) can result in significant mortality in Scottish salmon farms, but is considered to be a minor issue on trout farms. Controlling R. salmoninarum infection in trout to protect farmed salmon would be effective only if the risk posed from trout is significant both in absolute terms and relative to other potential sources of R. salmoninarum. To assess this, three complementary reviews are undertaken: review of data quality on BKD in Scotland and the national level prevalence and dynamics these data imply; case studies of recent BKD outbreaks in Scotland; and an assessment of the epidemiological and management factors that maintain and spread R. salmoninarum within and between the trout and salmon industries. These are then synthesised into a conclusion on the factors required for control of BKD in salmon. Most observed spread of R. salmoninarum occurred within single species or even companies, so the majority of cases in farmed salmon are linked to other salmon (and not to trout) farms. There is substantive geographical separation of areas of production for trout and salmon and transmission between salmon and trout networks is limited. The bacterium does not survive long in water so hydrodynamic transmission is likely to be localised. Currently R. salmoninarum is extremely rare in Scottish wild fish; this has not always been the case. Wild fish therefore probably play a limited role, but might act as reservoirs or vectors. The general conclusion is that to a large extent the transmission of R. salmoninarum in salmon and trout production can be separated and so there is potential to compartmentalise BKD controls, either by host species or geographical area. [Copyright &y& Elsevier]

The objective of this study was to obtain diagnostic performance estimates for immunofluorescence antibody test (IFAT) and quantitative polymerase chain reaction (qPCR) tests, for Bacterial Kidney Disease (BKD) surveillance in farmed Atlantic salmon (Salmo salar.) broodstock without clinical signs compatible with the disease in Chile. To obtain diagnostic sensitivity (DSe) and specificity (DSp) estimates of those tests, an expert elicitation process was conducted using the trial roulette method during a workshop with 18 national experts on BKD diagnostics and control. A questionnaire was given to the experts to gather information on their previous experience with BKD, and 12 experts who received an introduction to the expert-elicitation process and graphical representation of statistical distributions. Experts were divided into three groups and requested to draw distributions of DSe and DSp parameters using an online tool. Then figures where projected and discussed among participants. After the discussion round, experts were requested to redraw their distributions (if considered necessary). The agreement between groups was assessed by calculating the overlapping areas between the three distributions for each parameter. Finally, a consensus distribution was generated. In general, groups had moderate to high agreement with overlapping areas between 53% to 93% for DSp IFAT , DSe qPCR , and DSp qPCR. Conversely, no agreement was reached for the DSe IFAT distribution. Specifically, median estimates of 89.5%, 90.5%, and 95.9%, were obtained for DSp IFAT , DSe qPCR , & DSp qPCR , respectively. In the case of DSe IFAT , the first group provided a median estimate of 28%, whereas groups 2 and 3 reached a consensus value of approximately 62%. This study provides information that is not available in the country, and will help to adjust current BKD control programs, which mainly rely on the use of qPCR assays. • This research estimates diagnostic performance of IFAT and qPCR tests for BKD surveillance in Atlantic salmon broodstock. • To obtain diagnostic sensitivity (DSe) and specificity (DSp) estimates of those tests, an expert elicitation process was conducted using the trial roulette method. • Expert agreed in DSp IFAT , DSe qPCR , & DSp qPCR parameters with median estimates of 89.5%, 90.5%, and 95.9%, respectively. • No agreement was reached on DSe IFAT test performance among experts. [ABSTRACT FROM AUTHOR]