22 November: Update on medicines, resistance and control

The use of chemical treatment against sea lice in salmon farming has resulted in reduced effect and resistance against the different groups of compounds. One of the compounds, the organophosphate azamethiphos (AZA), exerts its effect on the acetylcholine esterase (AChE). This enzyme is essential in terminating nerve signals by cleaving the neurotransmitter acetylcholine in the synapse. A mutation in the AChE in salmon lice has been identified by our group and is directly related to a decrease in AZA sensitivity. To fully understand the effect of this mutation it is necessary to know more about the biochemical and physiological properties of AChE in salmon lice. To do so, work is on-going to describe catalytic properties of the different AChE variants, describe mRNA expression pattern and distribution of the enzyme in whole salmon louse sections. The work is carried out using different methods and techniques such as colorimetric assay for enzymatic activity, in situ hybridization and immuno-fluorescent antibody test.

Determination of resistance or reduced sensitivity against chemical treatments is usually based on bioassays of lice strains where the individual profiles are unknown. Since there is a strong correlation between individual survival of an AZA-treatment and the aforementioned mutation in the gene encoding AChE, we can use that knowledge to perform genotyping and analyse the catalytic properties of AChE in the same louse. Together with analysis of recombinant AChE this will make a very strong description of wild type versus mutated AChE in salmon lice.

07 March:  Medicines, resistance and control

In work package 1, led by Professor Tor Einar Horsberg at the Norwegian School of Veterinary Science (NSVS), the researchers explore salmon lice genetics connected to resistance mechanisms, salmon lice physiology and pharmaceutical compounds with effect against sea lice.

A very important scientific goal for the SLRC is to develop laboratory methods that evaluate the effect of intervention substances, for instance vaccines, novel medicinal products or anti-attachment feeds. Accurate counting of the correct number of salmon lice attached to the fish before and after exposure to a test substance is challenging. The youngest life-stages are quite small, and they partially hide between the fish shells, which make them hard to detect. Furthermore, preadult and adult stages tend to leave their hosts for a variety of reasons.

Therefore, one of the most important goals for WP1 is to develop a model of infection where the effects of all intervening means against salmon lice can be correctly predicted because the effect on all life cycles will be known.

The process of merging NSVS with the University of Life Sciences (UMB) is ongoing, and  yesterday, 07  March,  WP1 was one of the scientific projects introduced for representatives from the Department of Fisheries at Campus Ås. Lisbeth Berg-Hansen, the Norwegian Minister of Fisheries and Coastal Affairs, was present, and she showed great interest in the scientific work that was presented to her. One important observation is that even low concentrations of hydrogen peroxide, an anti-parasitic substance, inhibit hatching of salmon lice egg strings and development of infective larvae. Scientific work that results in hands-on knowledge like this is particularly welcomed by the industry, leading to a more effective way of reducing sea lice populations that have reduced sensitivity to medicinal products.

SLRC aims to work continuously with similar issues resulting in practical knowledge for the industry. Several interesting projects are currently in progress.