H Korsholm

Danish Veterinary and Food Administration, Glostrup, Capital Region, Denmark

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Publications (3)6.18 Total impact

  • Britt Bang Jensen · AK Ersbøll · Henrik Korsholm · HF Skall · NJ Olesen
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    ABSTRACT: Viral haemorrhagic septicaemia (VHS) is an economically very important fish disease in the northern hemisphere. When the VHS virus was first isolated in Denmark 50 yr ago, more than 80% of the 800 Danish fish farms were considered to be infected, but vigilant surveillance and eradication programmes led to a drastic reduction in prevalence, and finally, to complete eradication of VHS. Denmark thus obtained official status as an approved VHS-free member state within the European Union in November 2013. Data on outbreaks within the country have been collected since 1970, and here we combined these data with the geographical coordinates of fish farms to identify clusters of high disease prevalence and other risk factors. Our analyses revealed a statistically significant cluster in the southwestern part of the country, which persisted throughout the study period. Being situated within such a cluster was a significant risk factor for VHS. For freshwater rainbow trout farms situated inland, the number of upstream farms was a determining risk factor for VHS, as was distance to the nearest VHS-infected farm and year. Whether the farm used fresh or marine water in production did not have any influence on the risk of VHS, when accounting for whether the farm was situated inside a cluster of high risk. This information can be used when implementing risk-based surveillance programmes.
    No preview · Article · May 2014 · Diseases of Aquatic Organisms
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    ABSTRACT: Viral haemorrhagic septicaemia (VHS), caused by the novirhabdovirus VHSV, often leads to significant economic losses to European rainbow trout production. The virus isolates are divided into 4 distinct genotypes with additional subgroups including sublineage Ia, isolates of which are the main source of outbreaks in European rainbow trout farming. A significant portion of Danish rainbow trout farms have been considered endemically infected with VHSV since the first disease outbreak was observed in the 1950s. However, following a series of sanitary programs starting in 1965, VHSV has not been detected in Denmark since January 2009. Full-length G-genes of all Danish VHSV isolates that were submitted for diagnostic analyses in the period 2004-2009 were sequenced and analysed. All 58 Danish isolates from rainbow trout grouped with sublineage Ia isolates. Furthermore, VHSV isolates from infected Danish freshwater catchments appear to have evolved into a distinct clade within sublineage Ia, herein designated clade Ia-1, whereas trout isolates originating from other continental European countries cluster in another distinct clade, designated clade Ia-2. In addition, phylogenetic analyses indicate that VHSV Ia-1 strains have caused a few outbreaks in Germany and the UK. It is likely that viruses have been transmitted from infected site(s) out of the Danish environment, although a direct transmission pathway has not been identified. Furthermore, VHSV Ia-2 isolates seem to have been transmitted to Denmark at least once. Interestingly, one viral isolate possibly persisted in a Danish watershed for nearly 4 yr without detection whereas other subclades of VHSV isolates appear to have been eliminated, probably because of implemented eradication procedures.
    Full-text · Article · May 2012 · Diseases of Aquatic Organisms
  • B.D. Schyth · E Ariel · H Korsholm · N.J. Olesen
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    ABSTRACT: Detection of disease specific antibodies in farmed rainbow trout (Oncorhynchus mykiss) has been proposed as an alternative or supplement to the currently approved procedures for diagnosis and surveillance in this species. In samples from natural outbreaks of the disease viral haemorrhagic septicaemia (VHS) at two freshwater farms in southern Denmark serologic testing was used to broaden the diagnostic window from outbreak to diagnosis in the laboratory as compared to traditional procedures of isolation and identification of the virus. The serologic assay clearly increased the chance of detecting present or previous infections where the pathogen could not be isolated by standard methods (indicating older infections where the virus had been cleared). Our data allowed us to monitor the levels of neutralising antibodies in relation to the presence of the virus in fish experiencing two different types of outbreaks at two different farms. By sequence analysis of the viral glycoprotein from selected isolates we found no evidence for escape mutants having developed in the fish showing high titres of neutralising antibodies.
    No preview · Article · Apr 2012 · Fish & Shellfish Immunology