AN OUTBREAK OF HEMONCHOSIS ASSOCIATED WITH ANTHELMINTIC RESISTANCE ONA SHEEP FARM IN KENYA

An outbreak of haemonchosis associated with anthelmintic resistance wa s recorded in a flock of 150 Dorper sheep. Closantel (CLO) @ 5 mg kg(- 1) body weight and ivermectin (IVM)@ 0.2 mg kg(-1) body weight were 10 0% effective against Haemonchus contortus while fenbendazole (FBZ) and albendazole (ALE) reduced faecal egg counts by 27.5 and 38.0%, respec tively. Levamisole (LEV) showed an efficacy of 92.3%. At double the re commended dose (10 mg kg(-1)), percentage reduction in faecal egg coun ts of sheep treated with FBZ and ALE varied between 69.9 and 75.7% and worm counts between 38.3 and 42.0%. respectively, confirming Haemonch us contortus resistance to these anthelmintics. These data indicate th at worm control strategies based on CLO or IVM could provide effective control of benzimidazole-resistant strains of H. contortus on Kenyan farms.