title: Analysis of putative resistance gene loci in UK field populations of Haemonchus contortus after 6years of macrocyclic lactone use.
abstract: Sheep farmers in the UK rely on strategic anthelmintic use to treat and control gastrointestinal roundworms in their flocks. However, resistance to these drugs is now widespread and threatens the sustainability of sheep production. The mechanisms underlying resistance to the most commonly used class, the macrocyclic lactones, are not known and sensitive diagnostic tools based on molecular markers are not currently available. This prohibits accurate surveillance of resistance or assessment of strategies aimed at controlling its spread. In this study, we examined four UK field populations of Haemonchus contortus, differing in macrocyclic lactone treatment history, for evidence of selection at 'candidate gene' loci identified as determining macrocyclic lactone resistance in previously published research. Individual worms were genotyped at Hc-lgc-37, Hc-glc-5, Hc-avr-14 and Hc-dyf-7, and four microsatellite loci. High levels of polymorphism were identified at the first three candidate gene loci with remarkably little polymorphism at Hc-dyf-7. While some between-population comparisons of individual farms with and without long-term macrocyclic lactone use identified statistically significant differences in allele frequency and/or fixation index at the Hc-lgc-37, Hc-glc-5 or Hc-avr-14 loci, we found no consistent evidence of selection in other equivalent comparisons. While it is possible that different mechanisms are important in different populations or that resistance may be conferred by small changes at multiple loci, our findings suggest that these are unlikely to be major loci conferring macrocyclic lactone resistance on UK farms or suitable for diagnostic marker development. More powerful approaches, using genome-wide or whole genome sequencing, may be required to define macrocyclic lactone resistance loci in such genetically variable populations.
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, UK. Electronic address: Rosalind.Laing@gla.ac.uk.
authors.forename: Roz
authors.initials: R
authors.lastname: Laing
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, UK.
authors.forename: Kirsty
authors.initials: K
authors.lastname: Maitland
authors.affiliation: Department of Tropical Medicine, First Faculty of Medicine, Charles University in Prague, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Lecová
authors.affiliation: Moredun Research Institute, Pentlands Science Park, Penicuik, UK.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Skuce
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, UK.
authors.forename: Andy
authors.initials: A
authors.lastname: Tait
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, UK.
authors.forename: Eileen
authors.initials: E
authors.lastname: Devaney
mesh_terms: D000818:Animals; D004351:Drug Resistance / Q000235:genetics; D005260:Female; D005787:Gene Frequency; D014644:Genetic Variation; D060005:Genotyping Techniques; D006188:Haemonchiasis / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D006189:Haemonchus / Q000187:drug effects / Q000235:genetics*; D047029:Lactams, Macrocyclic / Q000494:pharmacology / Q000627:therapeutic use*; D007783:Lactones / Q000494:pharmacology / Q000627:therapeutic use*; D015810:Linkage Disequilibrium; D012150:Polymorphism, Restriction Fragment Length; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy / Q000469:parasitology*; D006113:United Kingdom
chemical_list: D047029:Lactams, Macrocyclic; D007783:Lactones
keywords: Anthelmintic resistance; Ivermectin; Macrocyclic lactone; Nematode; Parasite; Sheep