P-Glycoprotein-9 and anthelmintic resistance status in selected UK strains of the ovine gastrointestinal nematode Teladorsagia circumcincta

Turnbull, Francis (2014) P-Glycoprotein-9 and anthelmintic resistance status in selected UK strains of the ovine gastrointestinal nematode Teladorsagia circumcincta. PhD thesis, University of Glasgow.

Abstract

Throughout the world, control of parasitic nematodes in livestock has been compromised by the emergence and spread of anthelmintic resistance. Teladorsagia circumcincta is the most important gastrointestinal nematode parasite of small ruminants in temperate regions and the major resistant species in the United Kingdom (UK). In most cases the genetic factors which underpin resistance to broad-spectrum anthelmintics are still poorly understood.
Recent work conducted independently in New Zealand (NZ) and Scotland has implicated the involvement of a particular P-glycoprotein (Pgp) gene, Tci-pgp-9, in multiple-anthelmintic resistance in T. circumcincta. The focus of this study is to further characterise Tci-pgp-9 and its possible role in ivermectin (and multi-drug) resistance using two UK field isolates of T. circumcincta, one which is anthelmintic susceptible (MTci2) and another that is multiple-anthelmintic resistant (MTci5).
The generation of full-length cDNA sequence data from these isolates allowed genetic comparisons which identified the presence of nine non-synonymous SNPs in the Tci-pgp-9 coding sequence of the MTci5 isolate. The 3.8 kb, Tci-pgp-9 transcript from the MTci2 and MTci5 isolates shared 95.5 % identity at the nucleotide level and 99.5 % identity at the protein level. Twelve sequence variants were identified in the first internucleotide binding domain, designated Tci-pgp-9-IBDA, some of which shared a high level of identity with sequence variants identified in near-isogenic NZ strains. Multiple allelic variants were present in the majority of individuals, but a reduction in the number of allelic variants present in individuals of MTci5 relative to the MTci2 isolate was evident. A further reduction in the number of alleles present in individuals was also observed in individuals derived from an IVM treated population of MTci5, suggesting that IVM treatment applied purifying selection pressure. Quantitative real time PCR analysis showed a 3.7-fold increase in Tci-pgp-9 gene copy number in the MTci5 isolate relative to the MTci2 isolate, which was consistent with a 3.4-fold increase observed in the NZ study. None of the common haplotypes identified were unique to any given isolate, and the relationship between haplotype and copy number was not straightforward.
This study provides evidence that Tci-pgp-9 is under anthelmintic selection, but the precise role of this specific P-glycoprotein gene, and its alleles, in the phenotypic expression of anthelmintic resistance in T. circumcincta remains to be determined.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QH Natural history > QH301 Biology; Q Science > QH Natural history > QH426 Genetics
• Colleges/Schools: College of Medical Veterinary and Life Sciences
• Supervisor's Name: Skuce, Dr. Philip, Kenyon, Dr. Fiona, Jonsson, Dr. Nicholas and Bisset, Dr. Stewart
• Date of Award: 2014
• Depositing User: Mr Frank Turnbull
• Unique ID: glathesis:2014-5173
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 21 May 2014 11:09
• Last Modified: 29 May 2017 12:20
• URI: https://theses.gla.ac.uk/id/eprint/5173