Haemonchus contortus is one of the most pathogenic gastrointestinal parasites that infect small ruminants. The indiscriminate use of anthelmintics (i.e., benzimidazole class, BZ) to control infections has led to the reduction of drug efficacy in H. contortus populations worldwide. Resistance to BZ is associated with high frequencies of single nucleotide polymorphisms at F200Y, F167Y, and E198A positions of the β-tubulin isotype 1 gene. This study aimed to determine the frequency of single nucleotide polymorphisms associated with BZ resistance in H. contortus from 18 farms (545 sheep and 124 goats) in Paraná, Southern Brazil. Health management practices were identified as risk factors from individual farms. Genomic DNA was extracted from 20,000 larvae/farm and used in quantitative polymerase chain reaction assays for the three mutations. We ran a correlation analysis between flock health and quantitative polymerase chain reaction data. H. contortus was the most prevalent parasite in 67% (12/18) of the farms. Resistant allele frequencies were detected for F200Y (var. 46.4 to 72.0%) and F167Y (var. 15.7 to 23.8%). Only (100.0%) susceptible alleles were detected for the E198A. High treatment frequency (15/18), visual weight estimations for anthelmintic dose (15/18), no integration with other farm practices (14/18), treatment of all animals (14/18), and no quarantine period for newly acquired animals (10/18) were considered the most critical risk factors associated with BZ resistance. This is the first systematic prevalence study linking management practices on smallholder farms and the molecular data of BZ resistance of H. contortus in Southern Brazil.
Keywords: allelic mutations; control strategies; drug resistance; helminths; risk factors; small ruminants.