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Taksdal T.,National Veterinary Institute Oslo | Brun E.,National Veterinary Institute Oslo | Olsen A.B.,National Veterinary Institute Bergen | Breck O.,Marine Harvest Norway
Journal of Fish Diseases | Year: 2010

A cohort study was initiated in the spring of 2006 to investigate epidemiological aspects and pathogenesis of salmonid alphavirus (SAV) subtype 3 infections and pancreas disease (PD). The aims were to assess involvement of the freshwater production phase, the extent and frequency of subclinical infections and to follow PD-affected populations throughout the entire seawater production 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 included, 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 histopathological 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. Mortality levels following a PD diagnosis varied greatly between populations. The mean percentage mortality 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). © 2010 Blackwell Publishing Ltd. Source

Olsen A.B.,National Veterinary Institute Bergen | Nilsen H.,National Veterinary Institute Bergen | Sandlund N.,Norwegian Institute of Marine Research | Mikkelsen H.,Nofima Marin | Colquhoun D.J.,National Veterinary Institute Oslo
Diseases of Aquatic Organisms | Year: 2011

Coldwater-associated ulcers, i.e. winter ulcers, in seawater-reared Atlantic salmon Salmo salar L. have been reported in Norway since the late 1980s, and Moritella viscosa has been established as an important factor in the pathogenesis of this condition. As routine histopathological examination of winter ulcer cases in our laboratory revealed frequent presence in ulcers of long, slender rods clearly different from M. viscosa, a closer study focusing on these bacteria was conducted. Field cases of winter ulcers during 2 sampling periods, 1996 and 2004-2005, were investigated and long, slender rods were observed by histopathological examination in 70 and 62.5% of the ulcers examined, respectively, whereas cultivation on marine agar resulted in the isolation of yellow-pigmented colonies with long rods from 3 and 13% of the ulcers only. The isolates could be separated into 2 groups, both identified as belonging to the genus Tenacibaculum based on phenotypic characterization and 16S rRNA sequencing. Bath challenge for 7 h confirmed the ability of Group 1 bacterium to produce skin and cornea ulcers. In fish already suffering from M. viscosa-induced ulcers, co-infection with the Group 1 bacterium was established within 1 h. Ulcers from field cases of winter ulcers and from the transmission experiments tested positive by immunohistochemistry with polyclonal antiserum against the Group 1 bacterium but not the Group 2 bacterium. Our results strongly indicate the importance of the Group 1 bacterium in the pathogenesis of winter ulcers in Norway. The bacterium is difficult to isolate and is therefore likely to be underdiagnosed based on cultivation only. © Inter-Research 2011. Source

Habib C.,French National Institute for Agricultural Research | Houel A.,French National Institute for Agricultural Research | Lunazzi A.,French National Institute for Agricultural Research | Bernardet J.-F.,French National Institute for Agricultural Research | And 6 more authors.
Applied and Environmental Microbiology | Year: 2014

The genus Tenacibaculum, a member of the family Flavobacteriaceae, is an abundant component of marine bacterial ecosystems that also hosts several fish pathogens, some of which are of serious concern for marine aquaculture. Here, we applied multilocus sequence analysis (MLSA) to 114 representatives of most known species in the genus and of the worldwide diversity of the major fish pathogen Tenacibaculum maritimum. Recombination hampers precise phylogenetic reconstruction, but the data indicate intertwined environmental and pathogenic lineages, which suggests that pathogenicity evolved independently in several species. At lower phylogenetic levels recombination is also important, and the species T. maritimum constitutes a cohesive group of isolates. Importantly, the data reveal no trace of long-distance dissemination that could be linked to international fish movements. Instead, the high number of distinct genotypes suggests an endemic distribution of strains. The MLSA scheme and the data described in this study will help in monitoring Tenacibaculum infections in marine aquaculture; we show, for instance, that isolates from tenacibaculosis outbreaks in Norwegian salmon farms are related to T. dicentrarchi, a recently described species. © 2014, American Society for Microbiology. Source

Jakobsen R.A.,National Veterinary Institute Bergen | Heggebo R.,National Veterinary Institute Bergen | Sunde E.B.,National Veterinary Institute Bergen | Skjervheim M.,Nedre Norheim 36
Food Microbiology | Year: 2011

The aim of this study was to survey the presence of . Staphylococcus aureus and . Listeria monocytogenes during the cheese making process in small-scale raw milk cheese production in Norway.The prevalence of . S. aureus in bovine and caprine raw milk samples was 47.3% and 98.8%, respectively. An increase in contamination during the first 2-3 h resulted in a 73.6% prevalence of contamination in the bovine curd, and 23 out of 38 . S. aureus-negative bovine milk samples gave rise to . S. aureus-positive curds. The highest contamination levels of . S. aureus were reached in both caprine and bovine cheese after 5-6 h (after the first pressing). There was no contamination of . L. monocytogenes in caprine cheeses and only one (1.4%) contaminated bovine cheese.This work has increased our knowledge about . S. aureus and . L. monocytogenes contamination during the process of raw milk cheese production and gives an account of the hygiene status during the manufacture of Norwegian raw milk cheeses. © 2010 Elsevier Ltd. Source

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