No direct link between VHS virus isolated from Baltic herring and VHS disease in rainbow trout farms


<p>Viral Hemorrhagic Septicaemia (VHS) in rainbow trout is a highly contagious viral disease which causes high fish mortality rates and thus great financial losses to fish farms. In Finland, the VHS genotype Id was first diagnosed in 2000 in food fish farms in Åland and Pyhtää, since when it has been discovered each year, mainly in Åland. The virus does not affect humans.</p>

 The Finnish Food Safety Authority Evira has studied the role of Baltic herring as carriers of the VHS virus and spreaders of disease outbreaks, as Baltic herring has previously been used as rainbow trout feed. Between 2004 and 2006, a total sample of 7,560 Baltic herrings caught mainly from the Archipelago Sea (ten herrings per sample) was examined for the VHS virus, and it was diagnosed in 51 of the sample fish.

The highest number of infections was diagnosed in samples taken from the Archipelago Sea during spawning time. The VHS strain isolated from the Baltic herrings belonged to genotype II. VHS viruses from the same strain have previously been isolated from the Baltic herrings from Gotland Deep, as well as river lampreys caught in Kalajoki and Lestijoki. Marine VHS strains are divided into four genotypes, whereas the fresh water strains belong to genotype I. All four VHS virus genotypes are found in seawater, including genotype Id, discovered in Finnish food fish farms. This supports the presumption that fresh water viruses originate from the sea.

The study is not able to clarify the role of the Baltic herring in causing the disease. The virus isolated from the Baltic herring, and previously from the river lamprey, does not indicate a direct link to the disease outbreaks in marine food fish farms. However, it cannot be ruled out that the VHS virus genotype II may mutate in the future and causes diseases in fish farms.

The results of the study have recently been published in an international scientific publication:
Gadd, T. Jakava-Viljanen, M., Tapiovaara, H., Koski, P., Sihvonen, L.
Epidemiological aspects of viral haemorrhagic septicaemia virus genotype II isolated from Baltic herring, Clupea harengus membras L.
Journal of Fish Diseases 2011: 34, pp. 517-529.

For more information, please contact:
Tuija Gadd, Senior Researcher, Veterinary Virology Research Unit,
tel. +358 (0)50 357 0328, tuija.gadd at-merkki.gif : 1Kb

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