Scare J A, Lyons E T, Wielgus K M, Nielsen M K
M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
Vet Parasitol. 2018 Feb 15;251:112-118. doi: 10.1016/j.vetpar.2018.01.010. Epub 2018 Jan 16.
Equine cyathostomin are pervasive gastrointestinal parasites with wide-spread resistance to the benzimidazole and tetrahydropyrimidine drug classes worldwide. Combination deworming has been proposed as a more sustainable parasite control strategy. Simulation studies have found combination deworming to be effective in controlling drug resistant ovine trichostrongylid parasites. One equine study demonstrated an additive effect of a combination of oxibendazole and pyrantel pamoate against cyathostomins. However, this is the only equine study evaluating combination therapy, and the effects of repeated combination treatments administered over time remain unknown. The purpose of this study was to observe the efficacy of repeated oxibendazole/pyrantel pamoate combination therapy administered over one year against a cyathostomin population with resistance to benzimidazole and pyrantel products. Fecal egg counts were determined for the entire herd (N = 21) at the day of anthelmintic treatment and at two-week intervals for eight weeks post treatment. Starting efficacies of oxibendazole (OBZ, 10 mg/kg) and pyrantel pamoate (PYR, 6.6 mg base/kg) were 66.7% and 63.3%, respectively. Hereafter, the herd was treated four times with an oxibendazole/pyrantel pamoate combination, eight weeks apart, followed by repeating the single active treatments before concluding the study. While the first combination treatment exhibited an additive effect of the two active ingredients, this efficacy was not sustained over the course of the study. Mean fecal egg count reduction (FECR) was significantly greater for the first combination treatment (76.6%) than the second (42.6%, p = 0.0454), third (41.6%, p = 0.0318), and fourth (40.7%, p = 0.0372) combination treatments. The final single active mean FECRs were 42.3% for oxibendazole, and 42.7% for pyrantel pamoate. These efficacies were not significantly different from the initial single active efficacies (OBZ, p = 0.4421; PYR, p = 0.8361). These results suggest that combination therapy against double resistant equine cyathostomin populations is not sustainable, when using actives with markedly decreased starting efficacies.
马圆线虫是普遍存在的胃肠道寄生虫，在全球范围内对苯并咪唑和四氢嘧啶类药物具有广泛的抗性。联合驱虫已被提议作为一种更可持续的寄生虫控制策略。模拟研究发现联合驱虫对控制耐药性绵羊毛圆线虫寄生虫有效。一项针对马的研究表明，奥昔苯达唑和噻嘧啶莫能菌素联合使用对圆线虫有相加作用。然而，这是唯一一项评估联合疗法的马研究，长期重复联合治疗的效果仍然未知。本研究的目的是观察在一年时间内重复使用奥昔苯达唑/噻嘧啶莫能菌素联合疗法对一群对苯并咪唑和噻嘧啶产品耐药的圆线虫的疗效。在驱虫治疗当天以及治疗后八周内每隔两周对整个马群（N = 21）进行粪便虫卵计数。奥昔苯达唑（OBZ，10 mg/kg）和噻嘧啶莫能菌素（PYR，6.6 mg碱/kg）的起始疗效分别为66.7%和63.3%。此后，马群每隔八周用奥昔苯达唑/噻嘧啶莫能菌素联合治疗四次，然后在研究结束前重复单一活性药物治疗。虽然第一次联合治疗显示出两种活性成分的相加作用，但在研究过程中这种疗效并未持续。第一次联合治疗的平均粪便虫卵计数减少率（FECR）（76.6%）显著高于第二次（42.6%，p = 0.0454）、第三次（41.6%，p = 0.0318）和第四次（40.7%，p = 0.0372）联合治疗。最终单一活性药物的平均FECR，奥昔苯达唑为42.3%，噻嘧啶莫能菌素为42.7%。这些疗效与初始单一活性药物的疗效无显著差异（OBZ，p = 0.4421；PYR，p = 0.8361）。这些结果表明，当使用起始疗效明显降低的活性药物时，针对双重耐药的马圆线虫群体的联合疗法是不可持续的。
