Back to search

HAVBRUK2-Stort program for havbruksforskning

Deltamethrin resistance in the salmon louse Lepeophtheirus salmonis.

Alternative title: Deltametrin-resistens hos lakselus (Lepeophtheirus salmonis)

Awarded: NOK 1.6 mill.

In this project, the goal is to find out how salmon lice (Lepeophtheirus salmonis) can protect themselves from the effects of the antilouse compound deltamethrin (DMT), i.e. the mechanism(s) behind DMT resistance. Based on the results we had when the project started, a hypothesis on the resistance mechanism against DMT in salmon lice quite different from the mechanisms known from other animal groups was put forward. By crossing lice females from a resistant strain with males from a sensitive (non-resistant) strain and vice versa, and evaluating how descendants in the second generation withstand DMT treatment, we have shown that DMT-resistance in sea lice is maternally inherited. This phenomenon is described in the first article of this project. Offspring are known to have their genetic material as a mixture of their parents. In addition, all animals have a few genes that are independent of the other genes because they are not found in the nuclei of the cells. We find these genes in the mitochondria, the cells' energy producers. The mitochondria are transferred from mother to offspring. Thus, traits inherited through the maternal lineage may be genetically encoded in the mitochondrial genes. The hypothesis was therefore that markers for DMT resistance in salmon lice could be found in the mitochondrial genes and further that protection against DMT is linked to the function of the mitochondria. The mitochondrial genes of the salmon lice enrolled in the batch cross study was investigated and several differences between salmon lice from sensitive and resistant strains were detected. Some of these changes cause changes in the amino acid sequences of the corresponding proteins. Such changes may have a functional effect at the protein level and further affect the function of the mitochondria. To assess how mitochondria may be linked to DMT resistance in salmon lice, it was first investigated how DMT affects apoptosis (controlled cell death), since energy production failures can cause this. The results showed that DMT can affect the level of apoptosis and that this is different in resistant versus sensitive lice. This difference was greatest in muscle tissue. These results are published and support the hypothesis that mitochondria are involved and that DMT may affect mitochondrial function. It also appears that the levels of the energy molecules ATP and its degradation products differ in sensitive and resistant salmon lice after DMT exposure. The results of this trial are being prepared and will be published. Further studies in the project consisted of deciphering which proteins are possibly directly involved in the resistance mechanism. Together with collaborators in Belgium, a method was set up to separate the different mitochondrial complexes. These contain proteins that are genetically encoded in the mitochondrial genes. After separation, it is then possible to look at the effect of DMT on the complexes separately and compare the effect on sensitive salmon lice with resistant ones. Any effects can then be linked to the detected changes in the gene codes. Coincident differences in gene sequences and functional properties will indicate a link to resistance. This work was not completed within the project period but will be continued. In the last part of the project, DMT metabolism was studied. A total of over 800 salmon lice from a sensitive and resistant strain were exposed to one of three different concentrations of DMT. The amount of DMT and metabolites after exposure will give us knowledge of the differences between resistant and sensitive lice in metabolism. The results of this study will be published as soon as possible. Metabolic resistance is described for other arthropods and may be instrumental in the resistance mechanism of salmon lice. There is also a possibility that an effect on the mitochondria is due to one of the metabolites, and not the DMT molecules themselves. Whether this is the case must be examined in a separate study. The results of this project will be useful for accurately identifying which lice are resistant. In developing new drugs, it will also be important to know the real mechanisms of action and the mechanisms of resistance of existing drugs. This is to avoid the development of drugs with overlapping mechanisms, which will thus not be effective against already resistant lice.

Prosjektet har bidratt til økt internasjonalt samarbeid og nye kontakter. Dette samarbeidet vil fortsette også etter at prosjektperioden er over. Arbeidet med prosjektets hovedhypotese vil videreføres dersom nye søknader blir innvilget. Det vil da bli lagt mer fokus på hvordan den oppnådde kunnskapen kan overføres fra lakselus som et direkte mål for avlusningsmidler til andre arter som i utgangspunktet ikke er mål for behandling, og som potensielt er skadelidende. Videreføring av arbeidet vil også kunne påvirke hvordan det analyseres for pyretroid-resistens hos lakselus.

The project aims to unravel the resistance mechanism(s) in the salmon louse Lepeophtheirus salmonis towards the pyrethroid deltamethrin (DMT), which is used as an anti-parasitic drug. An increasing amount of results from studies on this issue support a novel resistance mechanism that differs from mechanisms described in other arthropods. It has been shown that DMT resistance in the salmon louse is maternally inherited, which is a rear phenomenon regarding any pesticide and pest. Several SNPs in the mitochondria genome has been linked to DMT resistance, indicating an involvement of the electron transport chain in the resistance mechanism in the salmon louse. From one study, it seems that approximately 70 % of the resistance can be explained by alterations in the mitochondria genome, whereas the last 30 % is still unknown. We have preliminary results that show that there are differences in the metabolism of DMT between susceptible and resistant lice strains, which could explain part of the resistance. A combination of biochemical and enzymatic assays, histochemistry, activity staining, in situ hybridization and molecular techniques will be used in the quest to determine the exact mechanism(s) of resistance in the salmon louse, by combining the hypothesis of mitochondria involvement and differences in metabolism. The unravelling of resistance mechanisms and genetic biomarkers enables the use of molecular tools to predict sensitivity in local lice populations. Thus, the knowledge generated in this post.doc. project can be used to reduce the misuse of substances with low treatment efficacy, the fish farmers can save money on reduced numbers of non-efficacious treatments, the number of stressful events on the fish due to chemical treatments can be minimized and the release of chemicals into the environment can be reduced. The knowledge of mode of action and resistance mechanisms is also valuable in the search for new anti-parasitic drugs.

Publications from Cristin

No publications found

No publications found

No publications found

No publications found

Funding scheme:

HAVBRUK2-Stort program for havbruksforskning