Efficacy of monepantel against lower developmental stages of a multi-resistant and susceptible Haemonchus contortus isolates: an in vitro study

Monepantel (MOP) belongs to a new class of anthelmintic compounds, the amino-acetonitrile derivates, which have a different mode of action as the currently used anthelmintics. Many present studies confirmed the high efficacy of MOP against fourth larval and adult stages of Haemonchus contortus. The objective of this study was to determine in vitro efficacy of MOP against lower development stages (eggs, L1–L3 larvae) and to compare it between resistant and susceptible isolates of H. contortus. For this purpose, two in vitro tests - egg hatch test and micro-agar larval development test were used. Results were quantified as 50 % lethal concentration (LC50), 99 % lethal concentration (LC99) and resistance factor (RF). This study revealed the high efficacy against lower larval stages (L1–L3) of both resistant and susceptible strains of this parasite. Larval susceptibility was not dependent of the sensitivity status of the nematode isolate. On the other hand, ovicidal effect of MOP was very low.