Abstract：
In Argentina, as in the rest of the world, cyathostomins are the most common nematodes parasitizing horses. Control is based almost exclusively on the administration of benzimidazoles, pyrimidines, and macrocyclic lactones. However, intensive use of these drugs is resulting in the development of anthelmintic resistance (AR). For example, AR to benzimidazoles is currently distributed throughout Argentina, while incipient AR to pyrimidines (pyrantel embonate) is appearing in areas where this drug is used. Macrocyclic lactones and especially ivermectin, are by far the most used drugs by the vast majority of equine premises in the country. Although ivermectin has been used since 1982, its efficacy against equine strongylid parasites has remained very high until the present. In this study we report for the first time, the presence of a cyathostomin population with resistance to ivermectin in adult horses belonging to an equine premise located in central Argentina. Fecal egg count reduction tests (FECRT) were performed following the most recent guidelines of the World Association for the Advancement of Veterinary Parasitology (WAAVP) for the diagnosis of anthelmintic resistance (research protocol) and resistance was considered when the Upper 90% Credible Interval fell below the expected efficacy threshold of 99.9%. Calculations were carried out using two different online calculation interfaces suggested by WAAVP. For the 14-day post-treatment interval, ivermectin efficacy was 79.5% (90% Credible Interval: 68.1-88.8) and 79.3% (74.2-83.6.3%) with the two methods, respectively. At 19 days post treatment, fecal egg count reductions were 68.6% (50.5-83.1) and 68.4% (61.9-74.1), respectively. At both intervals, this cyathostomin population fullfilled the criteria for AR. These findings suggest dispersion of ivermectin resistant cyathostomins in Argentina. Given the widespread use of macrocyclic lactones, it is important that veterinarians and the equine industry promote a more selective and evidence-based use of these drugs and establish routine monitoring to determine anthelmintic field efficacy to detect treatment failures as early as possible and avoid potential health problems as well as further spread of resistant genes.
摘要：
在阿根廷,和世界其他地方一样，cyathostomins是最常见的线虫寄生马。控制几乎完全基于苯并咪唑的给药，嘧啶,和大环内酯。然而,这些药物的大量使用导致驱虫耐药性（AR）的发展。例如,AR到苯并咪唑目前分布在整个阿根廷，而在使用这种药物的地区，出现了嘧啶（pyrantelembonate）的初期AR。大环内酯，尤其是伊维菌素，是迄今为止该国绝大多数马场使用最多的药物。尽管伊维菌素自1982年以来一直使用，但迄今为止，它对马强直性寄生虫的功效一直很高。在这项研究中，我们首次报告，在属于阿根廷中部马场的成年马中，存在对伊维菌素具有抗性的cyathostomin种群。根据世界兽医寄生虫学促进协会（WAAVP）的最新指南进行粪便卵数减少试验（FECRT），用于诊断驱虫药耐药性（研究方案），并且当上90％可信间隔低于99.9％的预期功效阈值时，就考虑了耐药性。使用WAAVP建议的两个不同的在线计算接口进行计算。对于治疗后的14天间隔，两种方法的伊维菌素疗效分别为79.5%(90%可信区间:68.1-88.8)和79.3%(74.2-83.6.3%),分别。治疗后19天，粪便卵数减少了68.6%(50.5-83.1)和68.4%(61.9-74.1)，分别。在这两个间隔，该cyathostomin人群满足AR的标准。这些发现表明伊维菌素抗性cyathostomins在阿根廷的分散。鉴于大环内酯的广泛使用，重要的是，兽医和马业促进更有选择性和循证的使用这些药物，并建立常规监测，以确定驱虫药场的疗效，尽早发现治疗失败，避免潜在的健康问题以及耐药基因的进一步传播。
