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New Findings About Cold-Water Vibrosis

NORWAY - Several different mechanisms involved in the development of cold water vibriosis have been identified a potentially important step towards the development of new treatment and vaccination strategies in fish farming.

Cold-water vibriosis is a disease which principally occurs in farmed salmon and is caused by the bacterium Vibrio salmonicida. Doctoral research by veterinary surgeon Ane Mohn Bjelland at The Norwegian School of Veterinary Science has identified a number of mechanisms that may hold the key to this bacterium's capacity to cause disease and survive in the environment.

By excreting substances similar to hormones, V. salmonicida can register the density of its own bacterial population and express different types of genes, depending on this density. Mohn Bjelland's doctoral study has shown that V. salmonicida uses this form of bacterial communication in order to ensure infection.

The study also revealed that environmental factors such as salt concentration and temperature play an important role in the development of cold water vibriosis and that the protein OmpU in V. salmonicida is important when it comes to the bacterium's resistance to the fish's immune defence system. This protein probably therefore contributes to the development of cold water vibriosis and may be a potential component in the development of a future vaccine.

Miss Mohn Bjelland's research has also demonstrated that V. salmonicida is dependent on its own mobility in order to be able to infect the salmon. After infection, the bacterium rapidly establishes itself in the fish's blood system, where it has optimal conditions for growing and spreading to other organs.

Her study shows that there is an absence of extracellular toxins in V. salmonicida and proposes that the tissue damage arising in the wake of the disease is more likely to be the result of an overstimulation of the fish's immune defence system and the subsequent death of cells. The doctoral thesis also suggests that the intestines of the salmon may act as a reservoir for V. salmonicida, which promotes the survival of the bacterium and its ability to infect.

New diseases are continually being discovered in fish farming. In order to ensure the sustainability of the industry, it is therefore essential to find out more about the causes of these diseases and about how they can be treated and combated.

Miss Mohn Bjelland's doctoral research has provided new insight into V. salmonicida's capacity to adapt itself and cause disease and may therefore contribute to an improvement in fish welfare and economic growth in the fish farming industry.

Ane Mohn Bjelland has worked at the Department of Bacteriology at The Norwegian School of Veterinary Science since February 2007. She defended her doctoral thesis, entitled ”Adaptation and virulence in Vibrio salmonicida”, at the School on 1st December 2011.

Charlotte Johnson

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