• Main Author: M Sandberg
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Atlantic salmon; cohort study; epidemi- ology; Sav’
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.464.4515; http://www.sfu.ca/cstudies/science/resources/1321655648.pdf

A cohort study was initiated in the spring of 2006 to investigate epidemiological aspects and patho-genesis of salmonid alphavirus (SAV) subtype 3 infections and pancreas disease (PD). The aims were to assess involvement of the freshwater pro-duction phase, the extent and frequency of sub-clinical infections and to follow PD-affected populations throughout the entire seawater pro-duction cycle, as well as investigate possible risk factors for PD outbreaks. Fish groups from 46 different Atlantic salmon freshwater sites in six counties were sampled once prior to seawater transfer and followed onto their seawater sites. A total of 51 Atlantic salmon seawater sites were in-cluded, and fish groups were sampled three times during the seawater production phase. SAV subtype 3 was not identified by real-time RT-PCR from samples collected in the freshwater phase, nor were any SAV-neutralizing antibodies or histopathologi-cal changes consistent with PD. In the seawater phase, SAV was detected in samples from 23 of 36 (63.9%) studied sites located within the endemic region. No SAV subtype 3 was detected in samples from seawater sites located outside the endemic region. The cumulative incidence of PD during the production cycle amongst sites with SAV detected was 87 % (20 of 23 sites). Average fish weight at time of PD diagnosis ranged from 461 to 5978 g, because of a wide variation in the timing of disease occurrence throughout the production cycle. Mor-tality levels following a PD diagnosis varied greatly between populations. The mean percentage mor-tality was 6.9 % (7.06) (range 0.7–26.9), while the mean duration of increased mortality following PD diagnosis was 2.8 months (1.11) (range 1–6).