Leathwick D M, Miller C M, Vlassoff A, Sutherland I A
AgResearch, Grasslands, Palmerston North, New Zealand.
Int J Parasitol. 1997 Apr;27(4):411-6. doi: 10.1016/s0020-7519(96)00193-2.
Lactating adult Romney ewes were infected, 4 weeks post-lambing, with benzimidazole (bz) resistant strains of Ostertagia circumcincta and Trichostrongylus colubriformis. Commencing 4 weeks after the initial infection the ewes were subjected to challenge 3 times weekly with 5000 L3 of bz-susceptible strains of both parasite species. At weekly intervals over the following 6 weeks, groups of ewes were drenched with a bz anthelmintic (oxfendazole) to remove bz-susceptible parasites and slaughtered to determine adult worm burdens of the bz-resistant parasites. The O. circumcincta infection declined exponentially with a mean daily death rate of 10.6% day-1 and no worms were recovered after 4 weeks or more of challenge. The T. colubriformis infection did not decline significantly over the 6 weeks of continuous challenge, indicating that the death rate could not be distinguished from zero. The upper 95% confidence limit for the death rate of T. colubriformis was 4.9%. The implications of these death rates on selection for drug resistance following ewe drenching during the post-partum period are discussed with selection pressure likely to be greater for T. colubriformis than for O. circumcincta.
产羔后4周的成年泌乳罗姆尼母羊感染了对苯并咪唑（bz）耐药的环形奥斯特他线虫和蛇形毛圆线虫毒株。在初次感染4周后，每周3次用5000条两种寄生虫的苯并咪唑敏感毒株的L3期幼虫对母羊进行攻击。在接下来的6周内，每隔一周，对几组母羊用苯并咪唑驱虫药（奥芬达唑）进行灌服，以清除对苯并咪唑敏感的寄生虫，然后宰杀母羊以确定对苯并咪唑耐药的寄生虫的成虫负荷。环形奥斯特他线虫感染呈指数下降，平均每日死亡率为10.6%/天，在攻击4周或更长时间后未发现线虫。在持续攻击的6周内，蛇形毛圆线虫感染没有显著下降，这表明死亡率与零没有区别。蛇形毛圆线虫死亡率的95%置信上限为4.9%。讨论了这些死亡率对产后母羊灌服药物后耐药性选择的影响，蛇形毛圆线虫的选择压力可能比对环形奥斯特他线虫更大。
