Allele specific PCR for a major marker of levamisole resistance in Haemonchus contortus

The presence and relative frequency detection of the levamisole-resistance-associated S168T substitution in hco-acr-8 in Haemonchus contortus

“…This observation is further reinforced by both the FECRT, and previous molecular testing done on most of these samples. Thus, as regards hco-acr-8 and its involvement in levamisole resistance in the parasite H. contortus , in our estimation, the data presented for S168T is so far more consistent with this mutation being a likely causal or closely-linked variant, associated with resistance, in comparison to the deletion in intron 2, which was readily found in both phenotypically susceptible and resistant isolates/populations ( Chagas et al, 2016 ; Baltrušis et al, 2021 ; Doyle et al, 2022 ; Antonopoulos et al, 2022 ). However, it should also be noted that S168T alone is unlikely to explain all cases of phenotypic resistance.…”

“…However, growing interest in hco-acr-8 and its role in resistance has resulted in findings inconsistent with this hypothesis ( Chagas et al, 2016 ; Baltrušis et al, 2021 ; Doyle et al, 2022 ). The most recent data suggests that a non-synonymous mutation (A G C→A C C; protein coding strand) in the exon 4 of this gene, resulting in the S168T substitution, could, instead, be the major determinant of levamisole resistance and serve as a potential molecular marker of its identification in parasite populations ( Doyle et al, 2022 ; Antonopoulos et al, 2022 ).…”

Functional validation of novel levamisole resistance marker S168T in Haemonchus contortus

“…Recently, a forward genetic cross between multidrug-resistant and drug-susceptible strains of H. contortus revealed a non-synonymous single nucleotide polymorphism (SNP) in acr- 8 that was strongly associated with LEV resistance ( Doyle et al, 2022 ). This SNP conferred a serine-to-threonine substitution (S168T) in exon 4, which was present in all LEV-resistant populations examined to date (including USA, South Africa, and Australia) and absent in all sensitive populations with available sequencing data ( Sallé et al, 2019 ; Antonopoulos et al, 2022 ; Francis et al, 2024 ). Furthermore, a serine-to-threonine substitution was present at the analogous position of acr-8 in LEV-resistant T. circumcincta after re-analysis of existing data ( Choi et al, 2017 ; Doyle et al, 2022 ).…”

3′-Demethoxy-6-O-Demethylisoguaiacin and Norisoguaiacin Nematocidal Lignans from Artemisia cina against Haemonchus contortus Infective Larvae

“…This parasite evades the host immune response and has developed mechanisms against anthelmintic commercial drugs [ 2 ]. Commercial anthelmintic molecules are the main strategies used for the control of H. contortus [ 3 ]. However, resistance has been growing and the commercial molecules have reduced efficacy [ 3 ].…”

“…Commercial anthelmintic molecules are the main strategies used for the control of H. contortus [ 3 ]. However, resistance has been growing and the commercial molecules have reduced efficacy [ 3 ]. Control may constitute an integrated parasite method such as herbolary [ 4 ].…”