Swedish University of Agricultural Sciences, Department of Biomedical Sciences and Veterinary Public Health, Division of Parasitology, Box 7036, 750 07 Uppsala, Sweden.
Institute for Experimental Pathology at Keldur, University of Iceland, Keldnavegur 3, 112 Reykjavik, Iceland.
J Parasitol. 2021 Jan 1;107(1):16-22. doi: 10.1645/20-91.
Horses in Iceland have been isolated for more than 1,000 yr but still harbor a similar range of gastrointestinal parasites as do horses across the world. The long isolation of the horses and their parasites presumably means that no resistance genes have been introduced into the Parascaris spp. population. It is therefore of particular interest to investigate the efficacy of ivermectin on Parascaris spp. infecting Icelandic foals. Potential treatment failure of ivermectin in Iceland will add substantial new information on how resistance can arise independently. This study aimed to determine the efficacy of subcutaneous injection of ivermectin for the treatment of Parascaris spp. infection in foals and to identify the Parascaris species present in the west and north of Iceland. A fecal egg count reduction (FECR) test (FECRT) was performed on 50 foals from 8 farms, including an untreated control group of 6 foals, from September to November 2019. The foals were between 3 and 5 mo of age at the start of the study and had not previously been treated with anthelmintic drugs. Each foal was treated subcutaneously with off-label use of Ivomec® injection 10 mg/ml or Noromectin® 1% at a dose of 0.2 mg/kg. The FECR for each farm was calculated in 2 ways, by the eggCounts package in R and by the Presidente formula (FECRT). Both calculation methods resulted in efficacy levels between 0% and 80.78%, indicating ivermectin resistance on all farms. We also confirmed, by karyotyping, that the species of equine ascarid present in the west and north of Iceland is Parascaris univalens. This study provides evidence for treatment failure of ivermectin against P. univalens infection in foals. Since Icelandic horses have been isolated on the island for more than 1,000 yr, this implies that resistance alleles have developed independently in the Icelandic Parascaris population. The actual clinical impact of ivermectin resistance is unknown but another drug of choice should be considered to treat Parascaris infection in foals in Iceland.
冰岛的马已经隔离了 1000 多年，但仍像世界各地的马一样，携带类似范围的胃肠道寄生虫。马及其寄生虫的长期隔离，推测意味着没有抗性基因被引入到 Parascaris spp. 种群中。因此，研究伊维菌素对感染冰岛小马驹的 Parascaris spp. 的疗效尤其有趣。伊维菌素在冰岛的潜在治疗失败将为抗性如何独立产生提供大量新信息。本研究旨在确定皮下注射伊维菌素治疗小马驹 Parascaris spp. 感染的疗效，并确定冰岛西部和北部存在的 Parascaris 物种。2019 年 9 月至 11 月，对来自 8 个农场的 50 匹小马驹进行了粪便虫卵减少（FECR）试验（FECRT），包括 6 匹未经治疗的对照组小马驹。研究开始时，小马驹年龄在 3 至 5 个月之间，此前未使用驱虫药物治疗。每匹马驹均以 0.2mg/kg 的剂量皮下注射非标签使用的伊维菌素注射液 10mg/ml 或 Noromectin® 1%进行治疗。通过 R 中的 eggCounts 包和 Presidente 公式（FECRT）以两种方式计算每个农场的 FECR。这两种计算方法的疗效水平均在 0%至 80.78%之间，表明所有农场的伊维菌素均有耐药性。我们还通过核型分析证实，在冰岛西部和北部存在的马蛔虫物种是 Parascaris univalens。本研究为伊维菌素治疗小马驹感染 P. univalens 失败提供了证据。由于冰岛马在该岛上已经隔离了 1000 多年，这意味着抗性等位基因已在冰岛 Parascaris 种群中独立发展。伊维菌素耐药性的实际临床影响尚不清楚，但应考虑另一种首选药物来治疗冰岛小马驹的 Parascaris 感染。
