Rapid selection for β-tubulin alleles in codon 200 conferring benzimidazole resistance in an Ostertagia ostertagi isolate on pasture
Abstract
Resistance to benzimidazoles (BZs) is widespread in sheep nematodes and increasing in those of cattle. Several reasons including the predominant use of pour-on anthelmintics and lack of scales in field conditions lead to under-dosing of cattle and therefore to increased selection pressure. In an field experiment the frequency of BZ-resistance associated allele (TAC) in codon 200 in the β-tubulin isotype 1 gene of Ostertagia ostertagi was monitored over one grazing season (approximately 30 weeks). Group 1, consisting of four calves, was experimentally infected with a pure O. ostertagi population displaying ∼50% of the TAC allele. The subsequently following groups of calves (four groups of two calves each) acquired natural infections by grazing contaminated pastures. Each group was treated with increasing percentages of sub-therapeutic dosages of albendazole (35-65%). Larvae obtained from faecal cultures pre and post treatment were subjected to species/genus-specific PCR as well as pyrosequencing to determine allele frequencies. PCR revealed the presence of Ostertagia, Trichostrongylus, Haemonchus and Cooperia in pre-treatment samples and predominantly Ostertagia as well as some Trichostrongylus in post treatment samples. Faecal ...Continue Reading
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Anthelmintics
Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. Discover the latest research on anthelmintics here.
Anthelmintics (ASM)
Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. Discover the latest research on anthelmintics here.