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A New, Pathogenic Bacterium Identified in Cod

by 5m Editor
19 February 2009, at 12:00am

Farmed cod have recently been hit by a serious disease caused by an unknown bacterium. In his doctorate, Jarle Mikalsen, Norwegian School of Veterinary Science contributed to the identification of this bacterium, now called Francisella philomiragia noatunensis.

The disease caused by the bacterium is now called francisellosis and is listed in the national disease register and regulated under the terms of the Norwegian Food Act.

Mikalsen's work with intracellular bacteria (bacteria living in body cells) of farmed cod and salmon has increased knowledge and improved the diagnostics of these bacteria. It has been an important contribution to the understanding of bacterial infections in the fish farming industry.


Colonies of Francisella in growth medium
Photo: Duncan Colquhoun, VI


Outbreaks of francisellosis along the coast

This thesis is the result of a collaboration by several Norwegian research environments. Its central goal was to increase our knowledge of bacterial infections of significance for health or economy in the farming industry. Mikalsen contributed to the development of new diagnostic methods for demonstrating pathogenic bacteria in Norwegian fish farming, and an important part of this work was the identification and characterisation of the bacterium Francisella philomiragia noatunensis.

This new bacterium has caused significant loss in the cod farming industry in recent years. However, it may also pose a threat to farmed salmon since it occurs naturally in coastal waters and is liable to cause disease in a range of marine species. The bacterium is not harmful to warm-blooded animals.

In addition to identifying Francisella, a breakthrough was achieved in the demonstration of the bacterium, Piscirickettsia salmonis. This is another intracellular bacterium that has caused significant loss in the fish farming industry both nationally and internationally, especially in Chile.

This doctorate produced six scientific articles and was carried out at the Norwegian Veterinary Institute in close collaboration with the research environment at the Norwegian School of Veterinary Science.

Cand. scient. Jarle Mikalsen defended his Ph. D. thesis, entitled "Diagnosis and characterisation of intracellular Gram-negative pathogens of marine and salmonid fish", at the Norwegian School of Veterinary Science, on November 21, 2008.

February 2009

5m Editor