No direct link between VHS disease found in rainbow trout farms and VHS virus carried by lamprey

8.3.2010

<p>Viral hemorrhagic septicaemia (VHS) of rainbow trout is a highly infectious viral disease, which causes high mortality rates in fish and thus results in financial losses in fish farms. Genotype Id of the VHS virus was for the first time found in Finland in 2000 in food fish farms in the Åland Islands and Pyhtää. It has since been detected on an annual basis; primarily in the Åland Islands.</p>

Finnish Food Safety Authority Evira has studied the significance of lamprey as carriers of the VHS virus and as vectors in outbreaks of the disease. River regulation projects have prevented the migration of fish and lamprey from the sea to the spawning areas upstream of the dam. The licence holder is required to move adult lamprey to the areas upstream of the regulation dam and to submit regulatory samples to viral disease analyses. Owing to this, a total of 2621 lamprey samples have been analysed in 1999–2008. The VHS virus was in 2003 isolated from 5 samples of lamprey caught in the rivers Kalajoki and Lestijoki. This was the first time the VHS virus has been isolated from lamprey ( Lampetra fluviatilis).

The virus strains isolated from lamprey represent genotype II. VHS viruses of this group have previously been isolated from herring caught in the Eastern Gotland Basin of the Baltic Sea. The VHS strains of the sea area are divided into four different genotypes, while freshwater strains represent genotype I. The most diverse VHS virus strains are found in seawater, including genotype Id, which has been detected in Finnish food fish farms at sea. This supports the conception of fresh water viruses originating from sea.

The strain isolated from lamprey in infection studies did not cause mortality in rainbow trout juveniles as the Id strain isolated from food fish farms did. The role of lamprey in the maintenance of the VHS virus remained an open question in our study. However, there is no link between the virus isolated from lamprey and the outbreaks of the VHS disease in our food fish farms at sea.

The results of the study have been published in an international scientific journal Dis Aquat Org (2010) 88: 189–198: (pdf, 594)
Gadd T, Jakava-Viljanen M, Einer-Jensen K, Ariel E, Koski P, Sihvonen L
Viral haemorrhagic septicaemia virus (VHSV) genotype II isolated from European river lamprey Lampetra fluviatilis in Finland during surveillance from 1999 to 2008.

For more information, please contact:
Senior Researcher Tuija Gadd, Veterinary Virology Research Unit, tel. +358 (0) 50 357 0328,
tuija.gadd at-merkki-kapea.gifevira.fi

 

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