科研之友
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摘要
The evolution of benzimidazoles (BZ) resistance in Teladorsagia circumcincta was investigated in a controlled trial with lambs submitted to different treatment regimens Four paddocks were seeded with a T circumcincta strain constituted by 25% of BZ-resistant nematodes Ten permanent lambs were allocated to each paddock from April to November in order to renew the contamination of pasture Monthly three tracer lambs were allocated in each paddock BZ-resistant nematode frequency was determined (PCR diagnosis) The faecal egg count reduction test (permanent lambs) and the number of nematodes in lambs were also determined (permanent and tracer lambs) Four different regimens of treatments were performed control levamisole (a non-BZ drug) fenbendazole (a BZ drug) and an alternation of levamisole and fenbendazole every second treatment The same protocol was repeated on two consecutive grazing seasons increasing the number of treatments (3 in first year and 5 in second year) The proportions of BZ-resistant nematodes did not change during all the study in both the control and the levamisole paddocks supporting an equal global fitness of BZ-resistant and susceptible nematodes Thus no reversion of BZ resistance is to be expected In the alternated drug group and in the BZ treated group BZ-resistant nematodes increased from 25% to 47% and to 78% respectively BZ resistance Increased proportionally to the selective pressure (number of BZ treatments) The drug alternation is not a good solution to delay importantly the evolution of resistance when more than 25% of nematodes are BZ-resistant This study is the first evaluation of BZ-resistance evolution (using individual genotyping) in controlled conditions It showed that when a monogenic anthelmintic resistance is esta
- 出版日期2010-8-27
