Facultad de Medicina Veterinaria y Zootecnia, Universidad Autonoma de Yucatan, Merida, Yucatan, Mexico.
Vet Parasitol. 2012 Mar 23;184(2-4):221-9. doi: 10.1016/j.vetpar.2011.09.017. Epub 2011 Sep 16.
A field survey was conducted to evaluate susceptibility of Rhipicephalus (Boophilus) microplus to cypermethrin on 49 farms in three areas of Yucatan, Mexico. The modified larval packet test was used to evaluate larval mortality at different cypermethrin concentrations. Dose-mortality regressions, lethal concentrations (LC(50)-LC(99)), confidence intervals and slope were estimated by probit analysis. Phenotype was defined as susceptible, tolerant or resistant when the resistance factor (RF) derived from both LC(50) and LC(99) determinations were <3, 3-5 or >5, respectively. An allele specific PCR (AS-PCR) was used to determine the frequency of a sodium channel mutation (F1550I, Phe→Ile) associated with pyrethroid resistance. Overall, 26.5%, 40.8% and 32.6% of tick populations were susceptible, tolerant and resistant to cypermethrin, respectively. A substantial inter-population variation in the level of cypermethrin response was evident (resistance factors ranged from 0.3 to 2599 and from 0.7 to >5000 when were indicated by the LC(50) and LC(99), respectively). The F1550I mutation (R allele) in R. microplus was present in all studied areas. The increasing presence of the R allele correlated well with increased levels of response indicated by both the LC(50) (r(2)=0.659, p=0.001) and LC(99) (r(2)=0.688, p=0.001) to cypermethrin. These results indicated that the F1550I mutation is a major common mechanism responsible for pyrethroid resistance in field populations of R. microplus ticks in the Mexican tropics. Both bioassay and AS-PCR showed that the prevalence of cypermethrin-resistant/tolerant R. microplus is high in Yucatan, Mexico and the relationship between the RF and the frequency of the R allele supports the role of F1550I as one of the most important mechanisms conferring pyrethroid resistance in these R. microplus populations.
在墨西哥尤卡坦的三个地区的 49 个农场进行了一项实地调查，以评估 Rhipicephalus (Boophilus) microplus 对氯菊酯的敏感性。使用改良幼虫包被测试来评估不同氯菊酯浓度下的幼虫死亡率。通过概率分析估计致死浓度（LC（50）-LC（99））、置信区间和斜率。表型定义为敏感型、耐受型或抗性型，当根据 LC（50）和 LC（99）测定得出的抗性因子（RF）分别小于 3、3-5 或大于 5 时。使用等位基因特异性 PCR（AS-PCR）确定与拟除虫菊酯抗性相关的钠离子通道突变（F1550I，苯丙氨酸→异亮氨酸）的频率。总体而言，26.5%、40.8%和 32.6%的蜱种群对氯菊酯分别表现为敏感型、耐受型和抗性型。氯菊酯反应水平的种群间存在明显的差异（当由 LC（50）和 LC（99）指示时，抗性因子分别为 0.3 至 2599 和 0.7 至>5000）。在所有研究区域都存在 R. microplus 中的 F1550I 突变（R 等位基因）。随着由 LC（50）（r（2）=0.659，p=0.001）和 LC（99）（r（2）=0.688，p=0.001）指示的反应水平的增加，R 等位基因的出现呈正相关。这些结果表明，F1550I 突变是热带墨西哥 R. microplus 田间种群对拟除虫菊酯产生抗性的主要共同机制。生物测定和 AS-PCR 均表明，在墨西哥尤卡坦州，氯菊酯抗性/耐受型 R. microplus 的流行率很高，RF 与 R 等位基因频率之间的关系支持 F1550I 作为赋予这些 R. microplus 种群对拟除虫菊酯抗性的最重要机制之一。
