Desmozoon lepeophtherii as a pathogen in Norwegian salmon aquaculture
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During late summer and autumn 2008 the Norwegian Veterinary Institute Bergen received several diagnostic cases with similar histopathological changes. Due to unknown cause of the the condition it was subsequently called autumn disease". Later on the microsporidian Desmozoon lepeophtherii was proposed associated with the autumn disease. D. lepeophtherii was also suggested associated with the development of pancreas disease (PD), heart and skeletal muscle inflammation (HSMI), cardiomyopathy syndrome (CMS) and proliferative gill inflammation (PGI) in farmed Atlantic salmon. In this study real time PCR and calcofluor white stain were used to detect D. lepeophtherii in formalin fixed paraffin embedded organ tissue used for diagnostic purposes. This was material and fish samples officially diagnosed with PD, HSMI, CMS and PGI in addition to autumn disease. The material was collected at the Veterinary Institute in Bergen from the years 2005, 2008 and 2009, and from the Veterinary Institute in Harstad year 2009. The main purpose of the study was to examine the presence of D. lepeophtherii in the diagnostic material and to evaluate a possible association between the microsporidian and any of these diseases. The results of the study showed no association between D. lepeophtherii and the diseases PD, HSMI and CMS. The results showed, however, an increased D. lepeophtherii burden in PGI samples and in the 2008 autumn disease individuals in material from Southern Norway. The results therefore indicate a possible association for D. lepeophtherii to the conditions autumn disease and PGI in farmed salmon from Southern Norway. In the material from Northern Norway the D. lepeophtherii burden was very low. In this material D. lepeophtherii was not associated with any disease condition. The study also showed that stored formalin fixed paraffin embedded material is very adequate for this type of work. The Norwegian Veterinary Institute has a large amount of historical diagnostic material that can be used for further studies on different disease conditions.