Dr JB Collins - Lack of canonical beta-tubulin resistance alleles in two benzimidazole-resistant ascarid species

Réalisation : 30 novembre 2021 Mise en ligne : 30 novembre 2021
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Management of nematode parasites of veterinary importance has become complicated because of the development of anthelmintic resistance. Resistance to benzimidazoles (BZ) is the most well characterized and has been linked to mutations in codons 167, 198, or 200 of the isotype-1 beta-tubulin gene in strongylid nematodes. Reports of BZ-resistance (BZ-R) in ascarids are rare, but we recently reported BZ-R in two ascarid species of poultry (Ascaridia dissimilis and Heterakis gallinarum) for the first time. We performed whole-genome sequencing to determine if any of the strongylid BZ-R alleles were present in these ascarids. Illumina short-read and PacBio long-read sequencing were carried out on individuals and pools of adult worms. Sequences were initially assembled and queried in BLAST searches using a beta-tubulin sequence from Ascaridia galli, a related ascarid of poultry. Contigs with beta-tubulin sequences were identified and then aligned for the codons of interest. From these genes, the ortholog of tbb-2, the most highly expressed beta-tubulin of ascarids, was identified and analysed at the codons of interest. No mutations associated with BZ-R were found in six samples from these BZ-R isolates. The lack of canonical alleles in beta-tubulin genes suggests that resistance may have taken a different evolutionary pathway in ascarids and that genetic investigations must extend beyond these codons and maybe even beta-tubulin genes.


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