Development of Anthelmintic Resistance in a Closed Sheep Flock
نویسنده
چکیده
Changes in anthelmintic resistance over the past 16 years is documented following the isolation of a field strain of Haemonchus contortus in sheep showing multiple anthelmintic resistance at Lawes in south eastern Queensland in 1979. Resistance to thiabendazole was first suspected in 1969 and continued to persist until the present time. In addition resistance to fenbendazole and oxfendazole also occurred and persisted for the entire period of the study. Resistance to levamisole ceased to exist after 3 years of withdrawal and remained highly effective even with regular challenge. Rafoxanide was moderately effective against the pre 1980 Lawes strain, but strong resistance developed after 3 years of exposure. Resistance to closantel developed after 25 exposures over a 9 year period. Ivermectin remained highly effective even after 10 applications over the past 6 years.
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