Gianchini Leonor Sicalo, Paras Kelsey L, George Melissa M, Howell Sue B, Storey Bob, Denwood Matthew J, Kaplan Ray M
Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, Georgia, USA.
Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, Georgia, USA; Bovine Dynamics, Kenmore, QLD, Australia.
Vet Parasitol. 2025 Jun;336:110435. doi: 10.1016/j.vetpar.2025.110435. Epub 2025 Mar 1.
Anthelmintic resistance (AR) in gastrointestinal nematodes (GIN) is a worldwide problem in all livestock production systems. Several prevalence studies performed internationally demonstrate that AR in cattle parasites is a growing problem; however, there are no published studies on prevalence in the United States (USA). In this study, we performed fecal egg count reduction tests (FECRT) on twelve cow-calf farms in Georgia, USA. On all farms the efficacy of eprinomectin pour-on (Eprinex®) and doramectin injectable (Dectomax®) was tested individually, as well as a combination treatment of doramectin injectable with oral fenbendazole (Safe-guard®). Fenbendazole was also tested individually on 7 farms, and long-acting eprinomectin (LongRange®) on one farm. FECRTs were performed, analyzed and interpreted following the 2023 WAAVP guidelines. Coprocultures were conducted to assess genus-specific efficacy. Overall, 100 % (12/12) and 75 % (9/12) of farms had resistance to at least one of the avermectin drugs tested in one or more GIN species, respectively. FECR ranged from 14.0 % to 96.8 % (mean=61.81 %) and 8.9-97.9 % (mean=66.87 %) for eprinomectin and doramectin, respectively; this difference was not significant (P = 0.924). In contrast, FECR for fenbendazole was high on all 7 farms tested, with just one farm demonstrating a low level of resistance. The combination treatment of doramectin plus fenbendazole was effective on all 12 farms (mean FECR=98.75 %), being significantly higher than for eprinomectin or doramectin (P≤0.001). Where coproculture data were sufficient to evaluate genus-specific reduction, resistance to Cooperia spp., Haemonchus spp. and Ostertagia spp. was present on 11/12 (92 %), 6/8 (75 %), and 4/10 farms (40 %), respectively. These data demonstrate that resistance to avermectin drugs is highly prevalent in Cooperia, Haemonchus, and Ostertagia on beef farms in Georgia. Though these data represent just one southern state, given the high level of movement of cattle in the USA, AR in GIN of cattle is likely to be highly prevalent throughout not only the southern USA, but across much of the country.
胃肠道线虫（GIN）的抗蠕虫药耐药性（AR）是所有畜牧生产系统中存在的一个全球性问题。国际上开展的多项流行率研究表明，牛寄生虫的抗蠕虫药耐药性问题日益严重；然而，美国尚无关于流行率的公开研究。在本研究中，我们在美国佐治亚州的12个肉牛繁殖场进行了粪便虫卵计数减少试验（FECRT）。在所有养殖场，分别对埃普利诺菌素浇泼剂（Eprinex®）和多拉菌素注射液（Dectomax®）的疗效进行了测试，同时也测试了多拉菌素注射液与口服芬苯达唑（Safe-guard®）的联合治疗效果。还在7个养殖场单独测试了芬苯达唑，在1个养殖场测试了长效埃普利诺菌素（LongRange®）。按照2023年世界动物寄生虫学协会（WAAVP）指南进行粪便虫卵计数减少试验的实施、分析和解读。进行粪便培养以评估属特异性疗效。总体而言，分别有100%（12/12）和75%（9/12）的养殖场对一种或多种GIN物种中测试的至少一种阿维菌素类药物产生了耐药性。埃普利诺菌素和多拉菌素的粪便虫卵计数减少率分别为14.0%至96.8%（平均值=61.81%）和8.9%至97.9%（平均值=66.87%）；差异不显著（P = 0.924）。相比之下，在所有测试的7个养殖场中，芬苯达唑的粪便虫卵计数减少率都很高，只有1个养殖场显示出低水平的耐药性。多拉菌素加芬苯达唑的联合治疗在所有12个养殖场均有效（平均粪便虫卵计数减少率=98.75%），显著高于埃普利诺菌素或多拉菌素（P≤0.001）。在粪便培养数据足以评估属特异性减少情况的地方，对库珀属、血矛线虫属和奥斯特他线虫属的耐药性分别出现在11/12（92%）、6/8（75%）和4/10个养殖场（40%）。这些数据表明，佐治亚州肉牛养殖场的库珀属、血矛线虫属和奥斯特他线虫属对阿维菌素类药物的耐药性非常普遍。尽管这些数据仅代表美国南部的一个州，但考虑到美国牛的流动程度很高，肉牛胃肠道线虫的抗蠕虫药耐药性不仅可能在美国南部高度流行，而且可能在该国大部分地区高度流行。
