Potential of Haemonchus contortus first-stage larvae to characterize anthelmintic resistance through P-glycoprotein gene expression

The high genetic diversity among different geographic isolates of Haemonchus contortus is considered a major hurdle to elucidating the mechanisms responsible for parasite multidrug resistance to commercial anthelmintics. Anthelmintic resistance can be assessed by the expression of resistance-related genes. Among them, P-glycoproteins (Pgp) have been extensively associated with anthelmintic resistance due to their role in drug efflux. Therefore, this study aimed to evaluate gene expression levels of nine Pgp (Pgp-1, Pgp-2, Pgp-3, Pgp-4, Pgp-9, Pgp-10, Pgp-11, Pgp-12, and Pgp-16) in eggs, first-stage larvae (L1), third-stage infective larvae (L3), adult female, and adult male of H. contortus from two isolates characterized as anthelmintic-resistant (R) and -susceptible (S). Four worm-free sheep were experimentally infected with approximately 4000 L3 larvae of H. contortus: two animals received L3 from the R isolate and two animals received L3 from the S isolate. Pgp-9 gene expression in all developmental stages of H. contortus was significantly higher (P < 0.05) in R isolate compared to S isolate. Higher expression (P < 0.05) of Pgp genes, except Pgp-4, was observed in L1 stage larvae from the R isolate. Our findings suggest that the L1 stage can be potentially used for anthelmintic resistance characterization through monitoring of different P-glycoproteins gene expression. These results may be useful in subsequent research to unveil anthelmintic resistance mechanisms in H. contortus without slaughtering sheep hosts, because L1 stages can be directly produced from eggs collected from feces.