Rapid selection for β-tubulin alleles in codon 200 conferring benzimidazole resistance in an Ostertagia ostertagi isolate on pasture
Rapid selection for β-tubulin alleles in codon 200 conferring benzimidazole resistance in an Ostertagia ostertagi isolate on pasture
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DOI：
10.1016/j.vetpar.2015.02.005
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发表时间：
2015-04-15
影响因子：
2.6
通讯作者：
Demeler, Janina
中科院分区：
文献类型：
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作者：
Knapp-Lawitzke, Friederike;Kruecken, Juergen;Demeler, Janina
对苯并咪唑类（BZ）的耐药性在绵羊线虫中广泛存在，在牛线虫中也在增加。几个原因，包括主要使用浇泼式驱虫剂和田间条件下缺乏鳞片，导致牛剂量不足，因此增加了选择压力。在田间试验中，在一个放牧季节（约30周）监测奥斯特线虫β-微管蛋白同种型1基因密码子200中BZ抗性相关等位基因（TAC）的频率。第1组，由4头小牛组成，实验感染纯O。ostertagi群体显示类似于50%的TAC等位基因。随后的小牛组（四组，每组两只小牛）通过放牧受污染的牧场获得自然感染。各组均以亚治疗剂量阿苯达唑的递增百分比（35-65%）进行治疗。对处理前和处理后从粪便培养物中获得的幼虫进行种/属特异性PCR以及焦磷酸测序以确定等位基因频率。PCR显示，在处理前样品中存在奥斯特线虫属、毛圆线虫属、血矛线虫属和古柏线虫属，在处理后样品中主要存在奥斯特线虫属以及一些毛圆线虫属。处理后7-10天，粪便虫卵计数减少始终小于90%。在自然感染的小牛中，治疗后TAC等位基因频率显著增加（p < 0.05），并且在放牧季节期间也迅速增加（治疗前：15-63%;治疗后：55-89%）。治疗前耐药基因型增加4倍以上表明，当亚治疗剂量与高治疗频率组合时，即使在温和的气候条件下和存在避难所时，BZ耐药性的选择也会发生得有多快。(C)2015 Elsevier B. V.版权所有。
Resistance to benzimidazoles (BZs) is widespread in sheep nematodes and increasing in those of cattle. Several reasons including the predominant use of pour-on anthelmintics and lack of scales in field conditions lead to under-dosing of cattle and therefore to increased selection pressure. In an field experiment the frequency of BZ-resistance associated allele (TAC) in codon 200 in the beta-tubulin isotype 1 gene of Ostertagia ostertagi was monitored over one grazing season (approximately 30 weeks). Group 1, consisting of four calves, was experimentally infected with a pure O. ostertagi population displaying similar to 50% of the TAC allele. The subsequently following groups of calves (four groups of two calves each) acquired natural infections by grazing contaminated pastures. Each group was treated with increasing percentages of sub-therapeutic dosages of albendazole (35-65%). Larvae obtained from faecal cultures pre and post treatment were subjected to species/genus-specific PCR as well as pyrosequencing to determine allele frequencies. PCR revealed the presence of Ostertagia, Trichostrongylus, Haemonchus and Cooperia in pre-treatment samples and predominantly Ostertagia as well as some Trichostrongylus in post treatment samples. Faecal egg count reduction was always less than 90% 7-10 days post treatment. In naturally infected calves TAC allele frequencies were significantly increased (p < 0.05) after treatment and they also rapidly increased during the grazing season (pre: 15-63%; post: 55-89%). The more than 4-fold increase in resistant genotypes before treatment indicates how fast selection for BZ resistance can occur when sub-therapeutic dosages are combined with a high treatment frequency, even under moderated climatic conditions and in the presence of a refugium. (C) 2015 Elsevier B.V. All rights reserved.