Infectious pancreatic necrosis virus regularly found in Finnish fish farms

15.11.2017 08:25

Finnish Food Safety Authority Evira has completed a study conducted in fish farms between 2000 and 2015 to determine the genetic characteristics of the virus that causes infectious pancreatic necrosis (IPN) in fish. IPN is a viral disease which causes financial losses in aquaculture across the world. The mortality rate caused by the IPN virus in Finnish fish farms has so far remained low. The disease is not contagious to humans and fish are not used as food at the juvenile stage when they are vulnerable to the disease.

As the disease is highly contagious, it is important to determine any potential changes in the genome of the virus to facilitate the monitoring of the spreading of the disease and to prevent spreading both in the wild and in fish farms. The viral disease is particularly found in juvenile salmonids e.g. rainbow trout and Atlantic salmon, but other fish species can also become infected.

Since 1987, the IPN virus has been found every year in asymptomatic fish in the Finnish sea areas. The virus spread to fish farms in inland waters in 2012, and since then has been found every year in several farms.

"Although the IPN virus has not caused high mortalities, part of the analysed fish manifested symptoms that are typical of the disease, such as darkening of the skin, distended abdomen, spiral swimming and histological changes. The virulence of the IPN virus is affected not only by the characteristics of the virus strain, but also by the age of the fish. Small juvenile fish are more susceptible to the disease than adult fish", concludes Senior Researcher, Ph.D. Riikka Holopainen from the Virology Research Unit of Evira.

IPN virus has spread to both coastal and inland water areas

The viruses that were analysed had been isolated from fish originating from both coastal and inland fish farms, and sent to Evira either for fish disease surveillance studies or for a diagnosis of the disease. The majority of the studied fish were rainbow trout, but there were also some Atlantic salmon, one trout and one whitefish.

The genome of the viruses was studied through sequencing, i.e., by determining the order of bases in the viral RNA. The results show that there are IPN viruses of three different genomic groups in Finland. According to the study, the prevalence of the different genomic groups varied depending on the geographical location and production type of the fish farm.

"Viruses of genomic group 2 were found in inland juvenile fish farms, while viruses of genomic groups 2, 5 and 6 were prevalent in coastal food fish farms. Genetic variance was relatively low in genomic groups 2 and 5; in other words, the viruses remained somewhat unchanged during the study period. The viruses of genomic group 6, on the other hand, were divided into two sub-groups. The partial sequence of the gene encoding the protein of the capsid structure of the virus was determined for all the virus strains included in the study, and for some of the strains, the whole genome of the virus was sequenced additionally", explains Researcher Anna Maria Eriksson-Kallio from the Veterinary Bacteriology and Pathology Research Unit.

The results of the study have been published in the scientifically peer-reviewed publication
Holopainen, R., Eriksson-Kallio, A.M., Gadd, T.
Molecular characterisation of infectious pancreatic necrosis viruses isolated from farmed fish in Finland. Archives of Virology 2017: Vol. 162, No. 11, pp. 3459 - 3471

For more information, please contact:
Riikka Holopainen, Senior Researcher, tel. +358 504393974
Anna Maria Eriksson-Kallio, Researcher, tel. +358 504392788