Fish farmers play an important role in the surveillance of fish diseases

11.12.2017 09:42

Samples of suspected diseases taken by fish farmers help with mapping viral haemorrhagic septicaemia (VHS) more effectively than the official disease surveillance of the EU. This was proven by the study completed at the Finnish Food Safety Authority Evira, where the occurrence of viral haemorrhagic septicaemia (VHS) was monitored from 2006 to 2009 in the containment area of Åland, where the disease was discovered for the first time in 2000. VHS is not transmitted to humans or other animal species, and the infected fish are not used as food.

VHS is a fish disease which requires control, and the authorities monitor its occurrence regularly in accordance with EU law.

After the year 2000, VHS spread quickly from one farm to most of the fish farms in Åland, causing financial losses. As many as one half of the infected rainbow trout shoals at the fish farms died in some cases.

"The study compared the official EU surveillance programme with three different programmes. One programme was based on surveillance according to the symptoms, in which the fish farmers participating in the study were committed to sending samples when they discovered signs of the disease in their fish. The surveillance by fish farmers proved to be 17 times more effective than the official EU surveillance programme", says Laboratory Manager Pia Vennerström from the Veterinary Bacteriology and Pathology Research Unit at Evira.

Two other surveillance programmes were similar to the official EU programme, but they included more frequent sampling and two new diagnostic methods for detecting a virus infection.

All samples were tested three times

All samples were studied using the official method, which is based on virus isolation in cell cultures and virus identification. The samples studied using cell cultures were also studied in parallel using a molecular biology method, which looks for the genome or RNA of the virus in the samples. The third method was used to find antibodies against the VHS virus in the blood of the fish.

"The molecular biology method proved to be at least as reliable as the cell culture method, and the antigen monitoring gave valuable information about the occurrence of viral infections when no symptoms had been observed in the fish shoal", Vennerström says.

The type of virus found in Åland has never been discovered in wild fish, and VHS has not been found in Åland since 2012.

The results of the study have been published in the peer-reviewed scientific publication
Vennerström, P., Välimäki, E., Lyytikäinen, T., Hautaniemi, M., Vidgren, G., Koski, P., Virtala, A.-M.
Viral haemorrhagic septicaemia virus (VHSV Id) infections in Finnish sea-reared rainbow trout farms were more consistently detected with syndromic rather than active surveillance. Diseases of aquatic organisms 2017: Vol. 126, pp. 111 - 123.

For further information, please contact:
Laboratory Manager Pia Vennerström, tel. +358 50 354 4603