Independent origins and non-parallel selection signatures of triclabendazole resistance in Fasciola hepatica.

Triclabendazole (TCBZ) is the primary treatment for fascioliasis, a global foodborne zoonosis caused by Fasciola hepatica. Widespread resistance to TCBZ (TCBZ-R) in livestock and a rapid rise in resistant human infections are significant concerns. To understand the genetic basis of TCBZ-R, we sequenced the genomes of 99 TCBZ-sensitive (TCBZ-S) and 210 TCBZ-R adult flukes from 146 bovine livers in Cusco, Peru. We identify genomic regions of high differentiation (FST outliers above the 99.9th percentile) that encod genes involved in the EGFR-PI3K-mTOR-S6K pathway and microtubule function. Transcript expression differences are observed in microtubule-related genes between TCBZ-S and -R flukes, both without drug treatment and in response to treatment. Using only 30 SNPs, it is possible to differentiate between TCBZ-S and -R parasites with ≥75% accuracy. Our outlier loci are distinct from the previously reported TCBZ-R-associated QTLs in the UK, suggesting an independent evolution of resistance alleles. Effective genetics-based TCBZ-R surveillance must consider the heterogeneity of loci under selection across diverse geographical populations.