Using feeding and motility patterns for ivermectin resistance detecting in Haemonchus contortus larvae

Resistance of Haemonchus contortus to ivermectin has become an increasingly serious problem worldwide. Drug-based control and management of this parasite requires reliable methods for testing drug resistance to evaluate and monitor their anthelmintic effects. In this study, the larval migration inhibition test (LMIT) and the larval feeding inhibition test (LFIT) were used to assess and compare seven strains of H. contortus, including one resistant and one susceptible strain from abroad (UKR and ASS, respectively), and five strains native to China (SXS, WMR, WSR1, WSR2, and WSR3). LFIT results showed that fluorescent-labeled Escherichia coli could be clearly observed after ivermectin (IVM) treatment inside UKR, WMR, WSR1, WSR2, and WSR3 larvae, but not inside ASS and SXS strains. Moreover, LMIT results showed that migration of SXS strain did not change significantly after IVM treatment compared with the susceptible ASS strain, whereas migration increased significantly in the UKR, WMR, WSR1, WSR2, and WSR3 strains. Taken together, SXS was found to be an IVM-susceptible strain, whereas WMR, WSR1, WSR2, and WSR3 were IVM-resistant strains. These results demonstrate that assessment of the motility and feeding ability of H. contortus larvae can be effectively used to determine resistance of H. contortus to IVM.