Abstract:
A strain of Haemonchus contortus from the Pietermaritzburg district of Natal was found to be resistant to levamisole (geometric mean efficacy 76,5 %), morantel (41,9 %), the benzimidazoles (oxfendazole: 33,7 %) and rafoxanide (82,0% ), but apparently fully susceptible to closantel and disophenol. In the case of ivermectin, a mean of 5.2 % of the H. contortus was not removed at a dosage of 200 µg kgˉ¹ live mass. A second strain of H. contortus, from Amsterdam in the south-eastern Transvaal, showed reduced susceptibility to levamisole (80,8%) and morantel (46,2% ), the only 2 drugs tested. This is apparently the first report of resistance to the levamisole/morantel group of anthelmintics in sheep in South Africa.
