M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
AgResearch, Grasslands Research Centre, Private Bag 11008, Palmerston North, 4442, New Zealand.
Int J Parasitol Drugs Drug Resist. 2020 Apr;12:28-34. doi: 10.1016/j.ijpddr.2019.12.002. Epub 2019 Dec 16.
An alternative control regimen for drug-resistant parasites is combination deworming, where two drugs with different modes of action are administered simultaneously to target the same parasite. Few studies have investigated this in equine cyathostomins. We previously reported that an oxibendazole (OBZ) and pyrantel pamoate (PYR) combination was not sustainable against a cyathostomin population with high levels of OBZ and PYR resistance. This study consisted of a field study and two computer simulations to evaluate the efficacy of a moxidectin-oxibendazole (MOX-OBZ) combination against the same cyathostomin population. In the field study, anthelmintic treatments occurred when ten horses exceeded 100 eggs per gram. Fecal egg counts and efficacy evaluations were performed every two weeks. The two simulations utilized weather data as well as equine and parasite population parameters from the field study. The first simulation repeated the treatment schedule used in the field study over a 40 year period. The second evaluated efficacies of combination treatments using selective therapy over 40 years. In the field study, efficacies of MOX and both combination treatments were 100%. The egg reappearance period for MOX was 16 weeks, and the two combination treatments were 12 and 18 weeks. The first (46.7%) and last (40.1%) OBZ efficacies were not significantly different from each other. In the simulation study, the combination treatment delayed MOX resistance development compared to when MOX was used as a single active. This occurred despite the low efficacy of OBZ. The second set of simulations identified combination treatments used with selective therapy to be the most effective at delaying MOX resistance. Overall, this study supports the use of combination treatment against drug-resistant cyathostomins, when one of the actives exhibits high efficacy, and demonstrates benefits of this approach despite substantially lowered efficacy of the other active ingredient.
一种替代耐药寄生虫的控制方案是联合驱虫，即同时使用两种作用模式不同的药物来针对同一寄生虫。很少有研究调查过马属动物旋毛虫的这种情况。我们之前报道过，奥昔布宁（OBZ）和吡喹酮（PYR）联合用药对高水平 OBZ 和 PYR 耐药的旋毛虫种群并不具有可持续性。本研究包括一项现场研究和两项计算机模拟，以评估莫昔克丁-奥昔布宁（MOX-OBZ）联合用药对同一旋毛虫种群的疗效。在现场研究中，当十匹马的粪便虫卵计数（FEC）超过 100 个/克时进行驱虫治疗。每两周进行一次粪便虫卵计数和疗效评估。两项模拟利用了气象数据以及现场研究中的马和寄生虫种群参数。第一项模拟在 40 年内重复了现场研究中使用的治疗方案。第二项模拟在 40 年内评估了选择性治疗联合用药的疗效。在现场研究中，MOX 和两种联合用药的疗效均为 100%。MOX 的虫卵再次出现时间为 16 周，两种联合用药的时间为 12 周和 18 周。第一次（46.7%）和最后一次（40.1%）OBZ 疗效之间无显著差异。在模拟研究中，与 MOX 单独使用相比，联合用药延迟了 MOX 耐药性的发展。尽管 OBZ 的疗效较低，但这一情况仍然出现。第二组模拟确定了在选择性治疗中使用联合用药是延迟 MOX 耐药性最有效的方法。总体而言，本研究支持在存在一种活性成分具有高疗效的情况下，使用联合用药治疗耐药旋毛虫，并证明了尽管另一种活性成分的疗效大大降低，但这种方法仍具有益处。
