Two field strains of Haemonchus contortus resistant to rafoxanide.

Abstract

Two field strains of Haemonchus contortus, one from Pretoria on the Highveld and the other from White River in the Lowveld of the Transvaal, showed pronounced resistance to rafoxanide at a dosage rate of 7.5 mg/kg live mass per os. Both of these strains originated from kikuyu pastures under irrigation. Resistance in South Africa to rafoxanide and other anthelmintics, namely, closantel, ivermectin and the benzimidazoles is reviewed. It is concluded that apart from avoiding farming practices where integrated worm control is not possible, there is at present no solution to the problem of worm resistance in the country.