THE EFFECTS OF ANTHELMINTICS ON OVINE LARVAL NEMATODE PARASITE MIGRATION IN-VITRO

The anthelmintics ivermectin, levamisole, morantel tartrate and thiabe ndazole all inhibited, in vitro, the motility of third stage larvae (L 3) of Trichostrongylus colubriformis. The bioassay, based on the inhib ition of L3 migration from apr gels, yielded sigmoid dose-response cur ves for ivermectin, levamisole and morantel tartrate, but not thiabend azole. The concentration of levamisole giving 50% inhibition of migrat ion (EC50) was determined for Cooperia curticei, Haemonchus contortus, Nematodirus spathiger, Ostertagia circumcincta, Trichostrongylus axei , T. colubriformis and T. vitrinus. EC50s differed between species but within species the EC50s for ensheathed and exsheathed L3 were simila r except for N. spathiger which showed significantly higher EC50 for t he ensheathed L3. No difference between EC50s for levamisole-resistant and susceptible strains of T. colubriformis were found. Similarly, mo rantel-resistant and susceptible stains of T. colubriformis could not be differentiated in this bioassay. The inhibition of L3 motility by k nown anthelmintic compounds in this bioassay suggests that the bioassa y could be used as a screen for potential new anthelmintics.