In vitro activity of paraherquamide against the free-living stages of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagiacircumcincta

Abstract

Paraherquamide, an oxindole alkaloid recently reported to have potent nematocidal activity, was shown to have a marked inhibitory effect on the motility of the free-living larval stages of H. contortus, T. colubriformis and O. circumcincta. The effect ofparaherquamide on larval motility could be distinguished from that caused by levamisole and the avermectins. After 72 h exposure, the concentration of paraherquamide required to inhibit the motility of 50% of L3 larvae present was 0.033, 0.058 and 2.7 μg ml −1 for O. circumcincta, T. colubriformis and H. contortus, respectively. Ivermectin (IVM)-resistant isolates of H. contortus were significantly more sensitive to the paralytic effects ofparaherquamide than IVM-susceptible isolates of this species. Paraherquamide had no effect on the time for development from the egg to the L3 larval stage of H. contortus, T. colubriformis and O. circumcincta.