School of Veterinary Medicine and Animal Science, Federal University of Mato Grosso do Sul, Campo Grande, Brazil.
Brazilian Agricultural Research Corporation, Embrapa Gado de Corte, Campo Grande, Brazil.
Prev Vet Med. 2020 Dec;185:105162. doi: 10.1016/j.prevetmed.2020.105162. Epub 2020 Oct 9.
The aim of the present study was to investigate the occurrence of Haemonchus contortus and Haemonchus placei in beef cattle and the frequency of single nucleotide polymorphisms associated with benzimidazole (BZ)-resistance in Haemonchus spp. in Brazil. For such, fecal samples were collected from 61 beef cattle ranches in 11 Brazilian states. Third-stage larvae (L3) were produced for morphological species identification and DNA extraction. PCR was performed for the analysis of the isotype 1 β-tubulin gene and the products were sequenced to confirm the presence of H. placei and H. contortus. For each field population, pyrosequencing assays were performed to quantify the frequency of the F167Y, E198A and F200Y polymorphisms in the isotype-1 β-tubulin gene. The results of the morphometric analysis of 2345 larvae showed that H. placei was present on all ranches. The analysis of the isotype 1 β-tubulin gene confirmed 100% prevalence for H. placei and 23.7% for H. contortus. Pyrosequencing assays demonstrated single-nucleotide polymorphisms (SNPs) associated with BZ-resistance in all three codons (F167Y, E198A and F200Y) of the isotype 1 β-tubulin gene in H. placei field populations. Frequencies of resistance-associated alleles above background (≥ 15%) were found for at least one codon in 11.4% of the field isolates and maximum frequencies of 30, 21 and 29% were found for codons 167, 198 and 200, respectively, on individual ranches. This study confirms the presence of H. contortus in beef cattle in the major livestock farming states in Brazil and demonstrates that genotypes associated with BZ resistance are present in field populations of Haemonchus spp..
本研究旨在调查巴西肉牛中旋毛虫（Haemonchus contortus）和弯角毛圆线虫（Haemonchus placei）的发生情况，以及与苯并咪唑（BZ）耐药相关的单核苷酸多态性（SNP）在 Haemonchus spp.中的发生频率。为此，从巴西 11 个州的 61 个肉牛牧场收集了粪便样本。产生第三期幼虫（L3）进行形态学种鉴定和 DNA 提取。进行 PCR 分析 1 型β-微管蛋白基因，产物测序确认存在弯角毛圆线虫和旋毛虫。对于每个田间种群，进行焦磷酸测序分析以定量测定 1 型β-微管蛋白基因中 F167Y、E198A 和 F200Y 多态性的频率。2345 条幼虫的形态测量分析结果表明，所有牧场均存在弯角毛圆线虫。1 型β-微管蛋白基因分析证实弯角毛圆线虫的流行率为 100%，旋毛虫的流行率为 23.7%。焦磷酸测序分析表明，在弯角毛圆线虫田间种群的所有三个密码子（F167Y、E198A 和 F200Y）中，与 BZ 耐药相关的单核苷酸多态性（SNP）均存在。在 11.4%的田间分离株中，至少一个密码子的耐药相关等位基因频率高于背景（≥15%），在单个牧场中，167、198 和 200 密码子的最大频率分别为 30%、21%和 29%。本研究证实了巴西主要畜牧业州肉牛中旋毛虫的存在，并表明与 BZ 耐药相关的基因型存在于 Haemonchus spp.的田间种群中。
