Department of Veterinary Science, Gluck Equine Research Center, University of Kentucky, Lexington, KY 40546-0099, USA.
Parasitol Res. 2010 Nov;107(6):1495-8. doi: 10.1007/s00436-010-2025-5. Epub 2010 Aug 17.
Critical tests were performed in 2009 and 2010 in four 2-year-old horses naturally infected with internal parasites. The horses were from a herd (Farm MC) where reduced activity of ivermectin and moxidectin on small strongyles was demonstrated previously from EPG (eggs/gram of feces) data in field tests. Also, in critical tests in horses from the same herd, ivermectin was less effective on immature small strongyles in the lumen of the large intestine than when the drug was first marketed. The main interest in the present critical tests was to determine the efficacy of moxidectin (400 μg/kg) on small strongyles. This was done to try and find indications of why there has been a return of strongyle EPG counts sooner after treatment in field tests than when moxidectin was first commercially available. Removal of adult small strongyles for the four treated horses was >99% to 100%. Efficacy on immature (L(4)) small strongyles was 82%, 96%, 98%, and >99% for the individual horses. Identification of small strongyles recovered from two of the horses revealed that three genera and 11 species were present. Specimens of Cylicocyclus ashworthi are reported for the first time in horses in Kentucky although eggs of this species have been identified. Moxidectin, in the present study, was excellent on removing adult small strongyles but was less effective on immatures (L(4)) in the intestinal contents. The question as to why moxidectin efficacy on small strongyles has declined in field tests may have been answered at least to a certain extent. It seems that a significant factor is "quick development" of a few remaining immatures in the gut lumen of horses. Also, possible activity may have decreased on encysted stages in the large intestinal lining. In any event, after treatment of some horses with moxidectin, the life cycle of small strongyles is shorter now than at the onset of usage of this compound.
2009 年和 2010 年，在 4 匹自然感染内部寄生虫的 2 岁马中进行了关键性测试。这些马来自一个牛群（Farm MC），此前在田间试验中通过 EPG（粪便中的卵/克）数据证明伊维菌素和莫昔克丁对小型圆线虫的活性降低。此外，在来自同一牛群的马的关键性测试中，伊维菌素对大肠腔中未成熟的小型圆线虫的效果不如该药首次上市时有效。本关键性测试的主要目的是确定莫昔克丁（400μg/kg）对小型圆线虫的疗效。这是为了尝试找出为什么在田间试验中，在使用莫昔克丁治疗后，强虫卵计数的回归时间比该药首次商业化时更早的原因。四匹治疗马的成年小型圆线虫清除率为>99%至 100%。对单个马的未成熟（L(4)）小型圆线虫的疗效分别为 82%、96%、98%和>99%。从两匹马中回收的小型圆线虫的鉴定表明，存在三个属和 11 个种。尽管已经鉴定出该物种的卵，但这是肯塔基州马中首次报告西里西库斯·阿什沃思（Cylicocyclus ashworthi）的标本。在本研究中，莫昔克丁在清除成年小型圆线虫方面非常出色，但在肠道内容物中的未成熟幼虫（L(4)）方面效果较差。关于为什么莫昔克丁对小型圆线虫的疗效在田间试验中下降的问题，至少在一定程度上已经得到解答。似乎一个重要因素是马肠道腔中少数未成熟幼虫的“快速发育”。此外，在大肠衬里的囊包阶段，其可能的活性也降低了。无论如何，在一些马用莫昔克丁治疗后，现在小型圆线虫的生命周期比该化合物开始使用时更短。
