Browsing by Subject "Animal Diseases"

Sort by: Order: Results:

Now showing items 1-1 of 1
  • Eriksson-Kallio, Anna Maria (Finnish Food Authority, 2022)
    Finnish Food Authority Research Reports 1/2022
    Infectious pancreatic necrosis (IPN) is a highly contagious viral disease of fish causing economic losses in farmed salmonid aquaculture worldwide. This research aimed to elucidate the epidemiological, pathological and genetic factors underlying IPNV infection occurring in farmed fish in Finland. The work was carried out by describing the epidemiology of an IPNV outbreak in Finnish inland waters in 2012–2014 and by characterizing the Finnish IPNV isolates occurring in inland waters using genetic, histopathological and immunological approaches. Furthermore, molecular characterization of Finnish IPNV isolates collected in 2000–2015 was performed. Finally, an infection trial was conducted to gather further information on the pathogenicity of three IPN genogroups in Finnish rainbow trout. IPNV genogroups 2, 5 and 6 have been found to occur in Finland. Of these, genogroup 2 is the most widespread. All three genogroups occur in the sea area. The IPNV epidemic starting in 2012 in inland waters was caused by genogroup 2. Retrospectively, a genetically similar viral strain to that of the inland strains was already found to occur in 2011 in the sea area, making it likely that the epidemic originated from the sea area. Molecular characterization of the isolated IPN viruses revealed little genetic variation within the Finnish genogroup 2 and 5 isolates. Finnish genogroup 2 isolates appeared to form their own subgroup, whereas genogroup 5 isolates formed a more consistent cluster with previously published isolates. Genogroup 6 consisted of two subgroups. The divergence of genogroup 6 IPNV within the aquabirnaviruses was further demonstrated by the sequence data from our studies. Prior to our studies, only partial VP1 genogroup 6 IPNV sequences were available at the NCBI GenBank. In our study, two IPNV genogroup 6 isolates were sequenced for the complete coding regions of viral genome segments A and B (polyprotein sequences). The Finnish IPNV isolates studied demonstrated virulence-associated amino acid patterns in the viral capsid protein (VP2) gene region previously associated with avirulence in genogroup 5, except for IPNV genogroup 6, which exhibits an amino acid pattern that has not been connected in the literature with either virulence or avirulence. In the infection trial, mortalities noted in all the treatment groups were only moderate at most. The highest mortalities were caused by the Finnish IPNV genogroup 5 (10.3% to 38.2%), whereas IPNV genogroup 2 caused variable mortalities (3.5% to 28.3%) and the Norwegian IPNV genogroup 5 virus used as a positive control caused only negligible mortalities. The IPNV genogroup 6 virus was not re-isolated in the infection trial, although some elevated mortalities were seen in one tank (8%), leaving the virulence of this genogroup still uncertain. Finnish inland waters harbour the most IPNV-susceptible life stages of fish, and here, an infection caused by a virulent strain of IPNV would thus potentially have the greatest negative economic impact on Finnish rainbow trout farming. Continuation of the legislative disease control of IPN genogroup 5 in Finnish inland waters is thus supported by this study. In general, IPN is considered a coldwater disease, with a peak in clinical disease and increased mortality at 10 °C. However, in Finland, the occurrence of virus at exceptionally high temperatures, with clinical signs of disease and histopathological changes typical of IPN, was noted at water temperatures as high as 21°C. The occurrence of IPNV in higher water temperatures has economic consequences, as it lengthens the susceptible time period for the disease. Moreover, rising water temperatures and longer warm water periods due to global warming may increase the disease-causing importance of this genogroup in the future.