Höglund Johan, Gustafsson Katarina, Ljungström Britt-Louise, Engström Annie, Donnan Alison, Skuce Philip
Department of Parasitology (SWEPAR), Swedish University of Agricultural Sciences, SE 751 89 Uppsala, Sweden.
Vet Parasitol. 2009 Apr 6;161(1-2):60-8. doi: 10.1016/j.vetpar.2008.12.001. Epub 2008 Dec 9.
A faecal egg count reduction test (FECRT) survey was conducted during the grazing season 2006 and 2007 to provide an updated indication of the prevalence of anthelmintic resistance in sheep flocks in Sweden. A total of 1330 faecal samples from 90 flocks on 45 farms, with a minimum of 20 ewes each, was collected by local sheep veterinarians. Per treatment group, approximately 15 lambs were dewormed either with oral suspensions of ivermectin (Ivomec vet.) or albendazole (Valbazen vet.). The efficacy on each farm was investigated either in 2006 or 2007 by faecal egg counts collected on the day of treatment and in a new sample from the same animals 7-10 days later. Third-stage larvae (L3) were initially identified morphologically from pooled cultures. These were then used as the source of genomic DNA template for two molecular tests. The first was a PCR-based test for specific identification of Haemonchus contortus, and the second was a Pyrosequencing assay for the analysis of benzimidazole (BZ) resistance targeting the P200 mutation in the parasite's beta-tubulin gene. Larval cultures indicated that Teladorsagia and Trichostrongylus were the predominant genera, but Haemonchus was diagnosed in 37% of the flocks. The PCR results revealed an almost 100% agreement with those farms that had previously been shown to have Haemonchus present, even when the % prevalence was low (approximately 3%). Only two (4%) of the surveyed farms showed evidence of BZ-resistant worm populations, with H. contortus being the species implicated according to post-treatment larval culture results. The Pyrosequencing assay detected BZ resistant allele frequencies of >40% in the Haemonchus-positive farms and 100% resistant alleles in the clinically most resistant farms. These preliminary results suggest that the FECRT is less sensitive than the molecular test at detecting BZ resistance. However, both tests need to be interpreted carefully, bearing in mind the relative proportions of species present and the starting egg and/or larval counts. Parasitological diagnosis of "clinical" resistance was also found against ivermectin in two flocks. However, both the pre-treatment FECs and the reductions in these were low, and only three lambs that had between 100 and 450 EPG after treatment were involved.
2006年和2007年放牧季节进行了粪便虫卵计数减少试验(FECRT)调查,以提供瑞典绵羊群抗蠕虫药耐药性流行情况的最新指标。当地绵羊兽医从45个农场的90个羊群中收集了总共1330份粪便样本,每个羊群至少有20只母羊。每个治疗组中,约15只羔羊分别用伊维菌素(Ivomec vet.)或阿苯达唑(Valbazen vet.)口服混悬液进行驱虫。2006年或2007年,通过在治疗当天收集粪便虫卵计数以及7 - 10天后从同一批动物采集的新样本,对每个农场的驱虫效果进行调查。三期幼虫(L3)最初通过混合培养物进行形态学鉴定。然后将这些幼虫用作两种分子检测的基因组DNA模板来源。第一种是基于PCR的检测,用于特异性鉴定捻转血矛线虫;第二种是焦磷酸测序分析,用于分析针对寄生虫β - 微管蛋白基因中P200突变的苯并咪唑(BZ)耐药性。幼虫培养表明,奥斯特线虫属和毛圆线虫属是主要属,但在37%的羊群中诊断出有血矛线虫。PCR结果显示,与之前已证明存在血矛线虫的农场结果几乎100%一致,即使流行率较低(约3%)。在接受调查的农场中,只有两个(4%)显示有BZ耐药虫群的证据,根据治疗后幼虫培养结果,涉及的虫种为捻转血矛线虫。焦磷酸测序分析在血矛线虫阳性农场中检测到BZ耐药等位基因频率>40%,在临床上耐药性最强的农场中检测到100%的耐药等位基因。这些初步结果表明,在检测BZ耐药性方面,FECRT比分子检测的敏感性低。然而,在考虑存在的虫种相对比例以及初始虫卵和/或幼虫计数时,两种检测都需要谨慎解读。在两个羊群中还发现了对伊维菌素的“临床”耐药性寄生虫学诊断结果。然而,治疗前的粪便虫卵计数及其减少量都很低,且仅涉及三只治疗后每克粪便虫卵数在100至450之间的羔羊。