van Doorn D C K, Ploeger H W, Eysker M, Geurden T, Wagenaar J A, Kooyman F N J
Vet Parasitol. 2014 Dec 15;206(3-4):246-52. doi: 10.1016/j.vetpar.2014.10.004.
The normal time interval between treatment of horses with a macrocyclic lactone (ML) and reappearance of strongyle eggs in the feces, or 'Egg Reappearance Period (ERP)', is at its shortest 8 weeks for ivermectin (IVM) and 12 weeks for moxidectin (MOX). Nowadays, it is not uncommon to find shorter ERPs, potentially indicating the beginning of the development of drug resistance. Whether all cyathostomin species contribute equally to a shortened ERP is not known. In the present study a Reverse Line Blot (RLB) on individual infective larvae was used to compare species composition before and after ML-treatment in horses with either a normal or a shortened ERP. Species composition was determined for a total of 21 horses on 4 farms and was based on differentiation of approximately 40 larvae per horse per sampling day. After IVM treatment the shortest ERP was found to be 28-42 days. After MOX treatment the shortest ERP was found to be 42-56 days. The RLB showed that early egg shedding was dominated by species of the genus Cylicocyclus (Cyc.) (Cyc. ashworthi, Cyc. insigne, Cyc. leptostomum and Cyc. nassatus). Before treatment, species composition was generally more diverse with species from several other genera also present. Interestingly, on the farm with the overall shortest ERP and where all horses showed a shortened ERP, more species/genera were present during early egg excretion than on other farms. Results suggest that cyathostomin species within the genus Cylicocyclus contribute to a shortened ERP more than species from other genera. However, if shortening of ERP overall becomes more pronounced and widespread within a farm, species from other genera will also be present during early egg shedding.
用大环内酯（ML）治疗马匹与粪便中圆线虫虫卵再次出现之间的正常时间间隔，即“虫卵再现期（ERP）”，伊维菌素（IVM）最短为8周，莫西菌素（MOX）最短为12周。如今，发现较短的ERP并不罕见，这可能表明耐药性开始发展。尚不清楚所有杯环线虫种类对缩短ERP的作用是否相同。在本研究中，对单个感染性幼虫进行反向线杂交（RLB），以比较ERP正常或缩短的马匹在ML治疗前后的种类组成。对4个农场的总共21匹马的种类组成进行了测定，每个采样日每匹马大约区分40个幼虫。IVM治疗后，最短的ERP为28 - 42天。MOX治疗后，最短的ERP为42 - 56天。RLB显示，早期排虫卵以杯环线虫属（Cyc.）的种类为主（阿氏杯环线虫、显著杯环线虫、细口杯环线虫和纳氏杯环线虫）。治疗前，种类组成通常更多样化，还存在其他几个属的种类。有趣的是，在ERP总体最短且所有马匹的ERP都缩短的农场，早期排虫卵期间出现的种类/属比其他农场更多。结果表明，杯环线虫属内的杯环线虫种类比其他属的种类对缩短ERP的作用更大。然而，如果农场内ERP缩短总体变得更加明显和普遍，其他属的种类在早期排虫卵时也会出现。
