Department of Biomedical Sciences and Veterinary Public Health (BVF), Section for Parasitology, Swedish University of Agricultural Sciences, Uppsala SE-751 89, Sweden.
Parasit Vectors. 2014 Jan 8;7:13. doi: 10.1186/1756-3305-7-13.
Anthelmintic resistance (AR) is an increasing problem for the ruminant livestock sector worldwide. However, the extent of the problem is still relatively unknown, especially for parasitic nematodes of cattle. The effect of ivermectin (IVM) (Ivomec inj.®, Merial) was investigated in Swedish isolates of gastrointestinal nematode (GIN) populations showing signs of AR in the field to further characterise the AR status by a range of in vivo and in vitro methods.
Three groups, each of 11 calves, were infected with an equal mixture of third stage larvae (L3) of Cooperia oncophora and Ostertagia ostertagi. Group A was inoculated with an IVM-susceptible laboratory isolate and groups B and C with isolates originating from 'resistant' cattle farms. Faecal egg counts (FEC) were monitored from 0 to 45 days post infection (d.p.i.), and L3 were harvested continuously for larval migration inhibition testing (LMIT) and species-specific PCR (ITS2). At 31 d.p.i., one calf from each group was necropsied and adult worms were recovered pre-treatment. At 35 d.p.i., calves from all groups were injected with IVM at the recommended dose (0.2 mg/kg bodyweight). At 45 d.p.i., another two animals from each group were sacrificed and established gastrointestinal worms were collected and counted.
A few animals in all three groups were still excreting eggs (50-150 per g faeces) 10 days post IVM injection. However, there was no significant difference in the FEC reductions in groups A (95%; 95% CI 81-99), B (98%; 92-100) and C (99%; 97-100) between 35 and 44 d.p.i. Furthermore, LMIT showed no significant difference between the three groups. Approximately 100 adult O. ostertagi were found in the abomasum of one calf (group B), whereas low to moderate numbers (400-12 200) of C. oncophora remained in the small intestine of the calves in all three groups at 45 d.p.i. PCR on L3 harvested from faecal samples up to 10 days post treatment showed a ratio of 100% C. oncophora in the calves inoculated with isolates A and B, whereas C also had 8% O. ostertagi.
Overall, this experiment showed that the animals were successfully treated according to the Faecal egg count reduction test (FECRT) standard (≥ 95% reduction). However, several adult worms of the dose-limiting species C. oncophora demonstrably survived the IVM treatment.
抗蠕虫药耐药性（AR）是全世界反刍动物养殖业日益严重的问题。然而，该问题的严重程度仍相对未知，特别是对于牛的寄生线虫。本研究采用伊维菌素（IVM）（伊维菌素注射液，默沙东）对显示田间 AR 迹象的瑞典胃肠道线虫（GIN）种群的分离株进行了研究，通过一系列体内和体外方法进一步描述了 AR 状态。
将三组各 11 头小牛感染无浆体属（Cooperia）第三期幼虫（L3）和奥斯特利希虫（Ostertagia）的混合感染。组 A 接种 IVM 敏感的实验室分离株，组 B 和 C 接种来自“耐药”牛场的分离株。从感染后 0 至 45 天（d.p.i.）监测粪便卵计数（FEC），并连续采集 L3 进行幼虫迁移抑制试验（LMIT）和种特异性 PCR（ITS2）。在 31 d.p.i.，每组一只小牛进行剖检，采集未处理的成虫。在 35 d.p.i.，所有组的小牛均按推荐剂量（0.2 mg/kg 体重）注射 IVM。在 45 d.p.i.，每组另外两只动物被处死，并收集和计数建立的胃肠道蠕虫。
三组中均有少数动物在 IVM 注射后 10 天仍在排出卵（每克粪便 50-150 个）。然而，在 35 至 44 d.p.i.之间，组 A（95%；95%CI 81-99）、B（98%；92-100）和 C（99%；97-100）的 FEC 降低率无显著差异。此外，LMIT 结果在三组之间无显著差异。在组 B 的一只小牛的皱胃中发现了约 100 条奥斯特利希虫成虫，而在 45 d.p.i.，三组小牛的小肠中均存在数量较低至中等的（400-12200 条）无浆体属幼虫。对治疗后 10 天内从粪便样本中采集的 L3 进行 PCR 检测显示，接种 A 和 B 分离株的小牛中 100%为无浆体属，而 C 中也有 8%的奥斯特利希虫。
总体而言，本实验表明，根据粪便卵计数减少试验（FECRT）标准（≥95%减少），动物得到了成功治疗。然而，几种剂量限制物种无浆体属的成虫显然耐受了 IVM 治疗。
