Risk factors for cardiomyopathy syndrome (CMS) in Norwegian salmon farming

Abstract

Cardiomyopathy syndrome (CMS) has been an economically important disease in Norwegian aquaculture since the 1990s. In this study, data on monthly production characteristics and case registrations were combined in a cohort study and supplemented with a questionnairebased case-control survey on management factors in order to identify risk factors for CMS. The cohort study included cases and controls from 2005 to 2012. From this dataset differences between all cases and controls were analyzed by a mixed effect multivariate logistic regression. From this we found that the probability of CMS increased with increasing time in the sea, infection pressure, and cohort size, and that cohorts which had previously been diagnosed with heart and skeletal muscle inflammation or which were in farms with a history of CMS in previous cohorts had double the odds of developing CMS. The model was then used to calculate the predicted value for each cohort from which additional data were obtained via the questionnaire-based survey and used as offset for calculating the probability of CMS in a semi-univariate analysis of additional risk factors. Finally, the model was used to calculate the probability of developing CMS in 100 different scenarios in which the cohorts were subject to increasingly worse conditions with regards to the risk factors from the dataset. We believe that this exercise is a good way of communicating the findings to farmers, so they can make informed decisions when trying to avoid CMS in their fish cohorts.

Cardiomyopathy syndrome in Atlantic salmon Salmo salar L.: A review of the current state of knowledge

“…Thus far, CMS outbreaks have only been observed in Atlantic salmon after transfer to sea, typically occurring during the second year of the seawater phase. In a study including all Norwegian salmon cohorts from 2004 to 2012, the median time from sea transfer to diagnoses of CMS was 16 months, with an interquartile range of 13–19 months and an average fish weight of 3.6 kg (Bang Jensen, Brun, Fineid, Larssen, & Kristoffersen, ). Cases of CMS have also been reported from fish groups as early as five to 6 months after sea transfer (Fritsvold et al., ; Wiik‐Nielsen et al., ).…”

“…In the above‐mentioned study (Bang Jensen et al., ), altogether 371 (16%) of the 2285 registered cohorts were diagnosed with CMS, and a study from 2003 found CMS registered in 14.6% of the spring smolt and 13.3% of the fall smolt groups, which were followed from sea entry until slaughter (Brun et al., ). As for seasonal variations, these are reported to be slight, although with an increase in cases in fall and spring (Kongtorp et al., ).…”

“…The virus shows increased replication over time in the cohabitants, who also develop cardiac changes typical of CMS (Haugland et al., ). In a field study from 2014, infection pressure was found to be one of the most important risk factors for disease diagnosis, underlining that CMS is usually spread horizontally, from farm to farm in sea water (Bang Jensen et al., ).…”

“…In conclusion, the primary route for transmission of CMS is horizontal (Bang Jensen et al., ; Timmerhaus, ), but vertical transmission of PMCV cannot be excluded (Wiik‐Nielsen, Lovoll, et al., ) and is therefore a focus of ongoing research.…”

Risk factors for outbreaks of infectious pancreatic necrosis (IPN) and associated mortality in Norwegian salmonid farming

“…(7) Infection pressure: Infection pressure was defined as exposure to infection by proximate infectious farms. Different scenarios for infection pressure were tested (see Bang Jensen et al 2013) with the following formula:…”