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Abstract：
This study quantified the extent of anthelmintic resistance (AR) in ascarid and strongylid nematodes against commonly used anthelmintics in Australian Thoroughbred horses. Faecal egg count reduction tests (FECRTs, n = 86) and egg reappearance period (ERP) tests were conducted on 22 farms across Australia. Faecal egg counts (FECs) were determined using the modified McMaster technique, and percent faecal egg count reduction (%FECR) was calculated using the Bayesian hierarchical model and hybrid Frequentist/Bayesian analysis method. The results were interpreted using old (published in 1992) and new (2023) research guidelines of the World Association for the Advancement of Veterinary Parasitology (WAAVP). The species composition of strongylid nematodes was detected utilising a DNA-metabarcoding method using pre- and post-treatment samples. Resistance was observed in strongylid nematodes to commonly used single-active and combination anthelmintics, including ivermectin (IVM %FECR range: 82%-92%; 95% lower credible interval (LCI) range: 80%-90%), abamectin (ABM: 73%-92%; 65%-88%), moxidectin (MOX: 89%-91%; 84%-89%), oxfendazole (OFZ: 0%-56%; 0%-31%) and its combination with pyrantel (OFZ + PYR: 0%-82%; 0%-78%). Resistance in Parascaris spp. was observed to IVM (10%-43%; 0%-36%), ABM (0%; 0%) and MOX (0%; 0%). When the new thresholds recommended by the WAAVP were used, AR was detected in six additional FECRTs for strongylids and three more tests for Parascaris spp., introducing resistance to OFZ and OFZ + PYR in the latter. Shortened ERPs (4-6 weeks) of strongylids were observed in 31 FECRTs in which AR was not detected at 2 weeks post-treatment for all the anthelmintics tested. Among cyathostomins, Cylicocyclus nassatus, Cylicostephanus longibursatus and Coronocyclus coronatus were the most prevalent species at 2 weeks post-treatment, whereas the main species appearing at five weeks following treatments with macrocyclic lactones were Cylicocyclus nassatus, Cylicostephanus longibursatus and Cylicocyclus ashworthi. After treatment with OFZ + PYR, the latter three, plus Coronocyclus coronatus and Cyathostomum catinatum, were detected at 5 weeks post-treatment. Overall, the study highlights the prevalence of AR in both ascarids and strongylid nematodes against commonly used anthelmintic products to control worms in Australian horses. The results indicate that ML combination products provided acceptable efficacy at 2 weeks. However, ERP calculations suggest that products work less effectively than previously measured. It is suggested to regularly monitor the efficacy of the anthelmintics and consider changing the worm control practices to better manage worms and AR in Australian horses.
摘要：
这项研究量化了asc虫和强线虫对澳大利亚纯种马常用驱虫药的驱虫抗性（AR）的程度。粪便卵数减少试验(FECRT，n=86）和卵再现期（ERP）测试在澳大利亚的22个农场进行。使用改良的McMaster技术测定粪便卵数（FECs），使用贝叶斯分层模型和混合频繁/贝叶斯分析方法计算粪便卵数减少百分比(%FECR)。使用世界兽医寄生虫学促进协会（WAAVP）的旧（1992年发布）和新（2023年）研究指南对结果进行了解释。使用处理前和后处理样品，使用DNA-metabarcoding方法检测了强线虫的物种组成。在强线虫中观察到对常用的单一活性和组合驱虫药的抗性，包括伊维菌素（IVM%FECR范围：82%-92%；95%低可信区间（LCI）范围：80%-90%），阿维菌素（ABM：73％-92％；65％-88％），莫西丁（MOX：89%-91%；84%-89%），恶芬达唑(OFZ:0%-56%;0%-31%)及其与吡喃酮的组合(OFZ+PYR:0%-82%;0%-78%)。寄生虫属的抗性。观察到IVM(10%-43%；0%-36%)，ABM(0%；0%)和MOX(0%；0%)。当使用WAAVP推荐的新阈值时，在另外六个FECRTs中检测到强直虫，在另外三个FECRTs中检测到AR。,在后者中引入对OFZ和OFZ+PYR的抗性。在31个FECRTs中观察到强衣原体的ERPs缩短（4-6周），其中所有测试的驱虫药在治疗后2周未检测到AR。在cyathostomins中，cylicocyclusnassatus,治疗后2周时最常见的物种是长骨骨病和冠状骨病，而大环内酯治疗后五周出现的主要物种是Cylicocycloclusnassatus，长骨节骨节骨节病和节骨节骨节。用OFZ+PYR治疗后，后三者,加上冠状红细胞和cyathostomumcetinatum，在治疗后5周检测到。总的来说,该研究强调了在asc虫和强力线虫中AR的患病率，相对于常用的驱虫药物，以控制澳大利亚马的蠕虫。结果表明ML组合产品在2周时提供可接受的功效。然而,ERP计算表明，产品的工作效率不如以前测量的。建议定期监测驱虫药的功效，并考虑更改蠕虫控制方法，以更好地管理澳大利亚马的蠕虫和AR。
