Laboratory for Parasitology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B-9820 Merelbeke, Belgium.
Vet Parasitol. 2012 Oct 26;189(2-4):378-82. doi: 10.1016/j.vetpar.2012.04.040. Epub 2012 May 9.
The main objective of the present study was to evaluate the accuracy of the faecal egg count reduction test (FECRT) to assess the resistance status of ivermectin (IVM)-resistant isolates of the cattle nematodes Ostertagia ostertagi and Cooperia oncophora, using the controlled efficacy test (worm counts) as a reference. The second objective was to investigate whether both IVM-resistant isolates showed side-resistance against moxidectin (MOX) under controlled conditions. Thirty male Holstein calves were experimentally infected with 25,000 L3 of an IVM-resistant O. ostertagi isolate and 25,000 L3 of an IVM-resistant C. oncophora isolate. Twenty-eight days later the calves were randomly divided into 2 treatment groups and 1 untreated control group. Animals in groups 1 and 2 received MOX (Cydectin(®) 1%, Pfizer) and IVM (Ivomec(®) 1%, Merial) respectively, by subcutaneous injection at a dose rate of 0.2mg/kg bodyweight. Faecal samples were collected 7 and 14 days after treatment and animals were necropsied 14/15 days post-treatment. Both the FECRT and the controlled efficacy test demonstrated that the O. ostertagi and C. oncophora isolates were resistant against IVM, with efficacies below 90%. The IVM-resistant O. ostertagia isolate was still susceptible to MOX treatment, as shown by over 99% reduction in egg counts and worm burden. The FECRT suggested borderline resistance against MOX in the IVM-resistant C. oncophora isolate, with egg count reductions between 97% (95% CI: 76; 100) at day 7 and 86% (95% CI: 49; 96) at day 14. However, the controlled efficacy test clearly showed MOX-resistance, with a decrease of only 31% (95% CI: -12; 57) in C. oncophora worm numbers. After MOX treatment, a significantly lower number of eggs per female C. oncophora worms was counted compared to the control group (43% reduction). Due to this reduced fecundity, the FECRT may fail to detect MOX-resistance.
本研究的主要目的是评估粪便卵计数减少试验（FECRT）评估伊维菌素（IVM）耐药的牛线虫 Osteragia ostertagi 和 Cooperia oncophora 分离株的耐药状态的准确性，以受控疗效试验（蠕虫计数）作为参考。第二个目标是调查在受控条件下，这两种 IVM 耐药分离株是否对莫昔克丁（MOX）表现出交叉耐药性。30 头雄性荷斯坦小牛用 25,000 个 IVM 耐药 O. ostertagi 分离株的 L3 和 25,000 个 IVM 耐药 C. oncophora 分离株的 L3 进行实验性感染。28 天后，小牛随机分为 2 个治疗组和 1 个未处理的对照组。第 1 组和第 2 组动物分别以 0.2mg/kg 体重的皮下注射剂量接受 MOX（Cydectin®1%，辉瑞）和 IVM（Ivomec®1%，默沙东）。治疗后 7 天和 14 天收集粪便样本，治疗后 14/15 天进行剖检。FECRT 和对照疗效试验均表明，O. ostertagi 和 C. oncophora 分离株对 IVM 具有耐药性，疗效低于 90%。IVM 耐药的 O. ostertagi 分离株对 MOX 仍敏感，卵计数和蠕虫负荷减少超过 99%。FECRT 表明 IVM 耐药的 C. oncophora 分离株对 MOX 呈边界耐药，第 7 天和第 14 天的卵计数减少分别为 97%（95%CI：76；100）和 86%（95%CI：49；96）。然而，对照疗效试验清楚地表明 MOX 耐药，C. oncophora 蠕虫数量仅减少 31%（95%CI：-12；57）。莫昔克丁治疗后，每只 C. oncophora 蠕虫的卵数明显低于对照组（减少 43%）。由于这种繁殖力下降，FECRT 可能无法检测到 MOX 耐药性。
