Assessing anthelmintic resistance risk in the post-genomic era: a proof-of-concept study assessing the potential for widespread benzimidazole-resistant gastrointestinal nematodes in North American cattle and bison

As macrocyclic lactone resistance becomes widespread in North American cattle and bison, producers are increasingly turning to benzimidazole drugs for parasite control. This study investigates whether the genetic foundations for benzimidazole resistance are already circulating within these parasite populations. The researchers employed deep-amplicon sequencing to scan for specific mutations in the isotype-1 beta-tubulin gene, which are known to confer resistance to benzimidazoles in various trichostrongylid nematode species.

The researchers discovered that several key mutations linked to benzimidazole resistance are present at low frequencies across multiple parasite species in cattle and bison populations throughout North America. This suggests that the genetic potential for resistance is not a future threat but an existing reality. Because these mutations are already circulating, a significant increase in the use of benzimidazole-based anthelmintics could rapidly select for these resistant variants, leading to widespread treatment failure.

This study serves as a proof-of-concept for using modern genomic surveillance to monitor anthelmintic resistance before it reaches clinical levels. By identifying resistance markers early, veterinarians and producers can make more informed decisions about parasite management strategies, potentially slowing the development of widespread resistance. This approach highlights the shift toward proactive, data-driven parasite control in the post-genomic era, moving away from reactive measures that only occur after drugs have already lost their efficacy.