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Abstract

By parasitizing livestock, gastrointestinal nematodes inflict a significant monetaryburden on the producers and compromise animal health as well as the sustainabilityof animal farming systems. To date, the most reliable way to control parasiticinfections in grazing livestock is through the use of anthelmintic drugs. However,decades of use have led to the parasites developing resistance. In small ruminants,one of the most pathogenic and prone to developing resistance is the parasiteHaemonchus contortus. This thesis aims to describe our most recent efforts to updatethe current knowledge on anthelmintic resistance in sheep nematodes by studying H.contortus in order to i) develop molecular tools to screen for mutations associatedwith resistance, ii) use these tools to carry out country-wide screenings for resistancemutations on Swedish sheep farms as well as iii) investigate potential, resistanceassociatedcandidate loci and genes through both the single-candidate and the genome-wide comparison approaches. We developed a sensitive droplet digital PCRbasedtool to screen for benzimidazole resistance-associated mutations and subsequentlyfound extremely high frequencies of the F200Y mutation but not F167Y inSwedish, field isolates of H. contortus collected over 6 years from 67 sheep farms.We also investigated the 63bp deletion in the hco-acr-8 as well as its role as a possiblemarker for levamisole resistance and found it to correlate with (but be an unreliablepredictor of) the resistant phenotype. Finally, we carried out a genome-widecomparison study between the ivermectin treated and untreated population andfound a region in chromosome V to show signs of recent selection, indicating theimportance of that locus in the development of ivermectin resistance in sheep nematodes.

Keywords

benzimidazole; levamisole; ivermectin; anthelmintic resistance; F200Y; hco-acr-8; droplet digital PCR; sequencing; GWAS; genome

Published in

Acta Universitatis Agriculturae Sueciae
2022, number: 2022:38
Publisher: Swedish University of Agricultural Sciences

SLU Authors

UKÄ Subject classification

Genetics and Genomics

Publication identifier

  • ISBN: 978-91-7760-951-3
  • eISBN: 978-91-7760-952-0

Permanent link to this page (URI)

https://res.slu.se/id/publ/118672