Effects of Emodepside on Egg Hatching, Larval Development and Larval Motility in Parasitic Nematodes

Abstract

The effects of the two anthelmintics PF1022A and emodepside were examined at the egg and free-living larval stages of several species of gastrointestinal nematodes. The in vitro assays used herein address the possible inhibitory effects of the cyclooctadepsipeptides (CODs) on egg hatching, larval development and larval motility. The egg hatch assay (EHA) and the larval development assay (LDA) were carried out using stages of Haemonchus contortus and cyathostomins of the horse. In the larval motility inhibition test (LMIT) only emodepside was used. The LMIT was performed with larval stages from Cooperia oncophora, Ostertagia ostertagi, H. contortus, Ancylostoma caninum and cyathostomins. To comparatively assess the effects of CODs and other anthelmintics, levamisole (LEV) and ivermectin (IVM) were also investigated. Ovicidal effects of the COD in the EHA were not observed even at the highest concentrations possible. The LDA showed the inhibitory activity of emodepside on larval development, which differed only slightly between the species tested. The LMIT demonstrated the inhibitory effects of emodepside on larval migration, with similar EC50 values across all species tested. The most susceptible species was A. caninum, the least susceptible was H. contortus. For all drugs tested a clear order of potency was observed: IVM was the most potent anthelmintic, LEV the least potent. With EC50 values of 2.25–8.28 μM, emodepside ranged between the two. In the present study the LDA and LMIT have been successfully established to monitor the activity of emodepside.