title: Phe362Tyr in AChE: A Major Factor Responsible for Azamethiphos Resistance in Lepeophtheirus salmonis in Norway.
abstract: Organophosphates (OP) are one of the major treatments used against the salmon louse (Lepeophtherius salmonis) in Norwegian salmonid aquaculture. The use of OP since the late 1970s has resulted in widespread resistant parasites. Recently, we reported a single mutation (Phe362Tyr) in acetylcholinesterase (AChE) as the major mechanism behind resistance in salmon louse towards OP. The present study was carried out to validate this mechanism at the field level. A total of 6658 salmon louse samples were enrolled from 56 different fish farms across the Norwegian coast, from Vest Agder in the south to Finnmark in the north. All the samples were genotyped using a TaqMan probe assay for the Phe362Tyr mutation. A strong association was observed between areas with frequent use of the OP (azamethiphos) and the Phe362Tyr mutation. This was confirmed at 15 sites where results from independently conducted bioassays and genotyping of parasites correlated well. Furthermore, genotyping of surviving and moribund parasites from six bioassay experiments demonstrated a highly significant negative correlation between the frequency of resistance alleles and the probability of dying when exposed to azamethiphos in a bioassay. Based on these observations, we could strongly conclude that the Phe362Tyr mutation is a major factor responsible for OP resistance in salmon louse on Norwegian fish farms.
authors.affiliation: NMBU School of Veterinary Science, Sea Lice Research Centre, PO Box 8146 Dep., NO-0033, Oslo, Norway.
authors.forename: Kiranpreet
authors.initials: K
authors.lastname: Kaur
authors.affiliation: Norwegian Veterinary Institute, Pb 750, N-0106, Oslo, Norway.
authors.forename: Peder Andreas
authors.initials: PA
authors.lastname: Jansen
authors.affiliation: PatoGen Analyse AS, Postboks 1527, 6025, Ålesund, Norway.
authors.forename: Vidar Teis
authors.initials: VT
authors.lastname: Aspehaug
authors.affiliation: NMBU School of Veterinary Science, Sea Lice Research Centre, PO Box 8146 Dep., NO-0033, Oslo, Norway.
authors.forename: Tor Einar
authors.initials: TE
authors.lastname: Horsberg
mesh_terms: D000110:Acetylcholinesterase / Q000235:genetics*; D019943:Amino Acid Substitution; D000818:Animals; D001681:Biological Assay; D033342:Copepoda / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D005838:Genotype; D007305:Insecticide Resistance / Q000187:drug effects*; D016015:Logistic Models; D009154:Mutation / Q000235:genetics; D017711:Nonlinear Dynamics; D009664:Norway; D063086:Organothiophosphates / Q000633:toxicity; D010649:Phenylalanine / Q000235:genetics*; D062206:Spatial Analysis; D014443:Tyrosine / Q000235:genetics*
chemical_list: D063086:Organothiophosphates; D014443:Tyrosine; D010649:Phenylalanine; C072763:azamethiphos; D000110:Acetylcholinesterase