背景:拟除虫菊酯化学品是用于对抗蜱的主要杀螨剂之一。据报道,对这些化学物质的抗性与微型Rhipicephalusmicroplus的电压门控钠通道(VGSC)基因突变有关。本研究调查了中国广西地区对拟除虫菊酯的微生物耐药性,标志着这一领域的第一批研究工作之一。这些发现旨在为有效实施局部蜱控制策略提供重要的基线。
方法:2021年3月至7月,从广西5个地级市采集了447份R.microplustick样本。等位基因特异性聚合酶链反应(AS-PCR)用于扩增VGSC中II结构域S4-5接头的C190A和G215T以及III结构域S6的T2134A,检测与拟除虫菊酯杀螨剂抗性相关的核苷酸突变。随后进行了分析以确定患病率,突变类型,和样本群体内的基因型分布。
结果:在所有五个研究的R.microplus种群中鉴定了VGSC基因内的突变,尽管突变率总体上仍然很低。具体来说,最普遍的突变是C190A,在4.9%的样品中观察到(22/447),其次是G215T,占4.0%(18/447),和T2134A为1.3%(6/447)。VGSC基因的三个关键位点的突变分布揭示了四种不同的突变类型:C190A,G215T,C190A+G215T,和T2134A。值得注意的是,单突变C190A突变频率最高,占4.3%,C190A+G215T组合最低,只有0.7%。该分析进一步确定了七个基因型组合,野生型组合C/C+G/G+T/T占主导地位,频率为90.4%。随后,以4.3%的频率观察到C/A+G/G+T/T组合,而C/C+T/T+T/T组合表现出最低的频率(0.2%)。此外,在所有三个位点均未检测到同时突变.突变类型的地理差异很明显。从河池到崇左市的两个样本都表现出相同的三种突变类型;但是,C190A在河池市最为流行,而G215T在崇左占主导地位。相比之下,北海至桂林的样本均仅表现出一种突变类型:G215T发生在12.5%(4/32)的北海样本中,和C190A在7.5%(4/53)的桂林样品中。
结论:这些发现强调了广西与拟除虫菊酯耐药相关的R.microplus中VGSC基因突变的频率相对较低,中国。此外,不同地区的突变类型和基因型分布的差异凸显了在tick种群中监测和管理拟除虫菊酯抗性时需要区域化策略。这种分子监测对于告知有针对性的控制措施和减轻广泛耐药性出现的风险至关重要。
BACKGROUND: Pyrethroid chemicals are one of the main acaricides used against ticks. Resistance to these chemicals has been reported to be associated with mutations in the voltage-gated sodium channel (VGSC) gene of the
Rhipicephalus microplus. This study investigates R. microplus resistance to pyrethroids in Guangxi region of China, marking one of the first research efforts in this area. The findings are intended to provide vital baseline for the effective implementation of localized tick control strategies.
METHODS: From March to July 2021, 447 R. microplus tick samples were collected from five prefecture-level cities in Guangxi. Allele-specific polymerase chain reaction (AS-PCR) was used to amplify segments C190A and G215T of the domain II S4-5 linker and T2134A of domain III S6 in the VGSC, to detect nucleotide mutations associated with resistance to pyrethroid acaricides. Subsequent analyses were conducted to ascertain the prevalence, types of mutations, and genotypic distributions within the sampled populations.
RESULTS: Mutations within VGSC gene were identified across all five studied populations of R. microplus, although the mutation rates remained generally low. Specifically, the most prevalent mutation was C190A, observed in 4.9% of the samples (22/447), followed by G215T at 4.0% (18/447), and T2134A at 1.3% (6/447). The distribution of mutations across three critical sites of the VGSC gene revealed four distinct mutation types: C190A, G215T, C190A + G215T, and T2134A. Notably, the single mutation C190A had the highest mutation frequency, accounting for 4.3%, and the C190A + G215T combination had the lowest, at only 0.7%. The analysis further identified seven genotypic combinations, with the wild-type combination C/C + G/G + T/T predominating at a frequency of 90.4%. Subsequently, the C/A + G/G + T/T combination was observed at a frequency of 4.3%, whereas the C/C + T/T + T/T combination exhibited the lowest frequency (0.2%). Additionally, no instances of simultaneous mutations at all three sites were detected. Geographical differences in mutation types were apparent. Both samples from Hechi to Chongzuo cities exhibited the same three mutation types; however, C190A was the most prevalent in Hechi, while G215T dominated in Chongzuo. In contrast, samples from Beihai to Guilin each exhibited only one mutation type: G215T occurred in 12.5% (4/32) of Beihai samples, and C190A in 7.5% (4/53) of Guilin samples.
CONCLUSIONS: These findings underscore the relatively low frequency of VGSC gene mutations in R. microplus associated with pyrethroid resistance in the Guangxi, China. Moreover, the variation in mutation types and genotypic distributions across different locales highlights the need for regionalized strategies in monitoring and managing pyrethroid resistance in tick populations. This molecular surveillance is crucial for informing targeted control measures and mitigating the risk of widespread resistance emergence.