Department of Zoology, Entomology Unit, University of Ilorin, Ilorin, Kwara State, Nigeria; Department of Public Health and Epidemiology, Molecular Entomology and Vector Control Research Laboratory, Nigerian Institute of Medical Research, Yaba, Lagos State, Nigeria; Department of Biological Sciences, Lagos State Polytechnics, Ikorodu, Lagos, Nigeria.
Department of Zoology, Entomology Unit, University of Ilorin, Ilorin, Kwara State, Nigeria.
Acta Trop. 2022 Mar;227:106291. doi: 10.1016/j.actatropica.2021.106291. Epub 2021 Dec 24.
Malaria is a major public health challenge in Africa with Nigeria accounting for the highest burden of the disease in the world. Vector control has proved to be a highly effective component of malaria control, however, the development and spread of insecticide resistance in major vectors of malaria have been a major challenge. This study assessed resistance mechanisms in Anopheles coluzzii populations from Kosofe, Lagos mainland and Ojo Local Government Areas in Lagos, Nigeria where An. gambiae s.l is resistant to DDT and Permethrin. WHO susceptibility bioassay test was used in determining resistance status of An. coluzzii to discriminating doses of DDT and Permethrin while synergist assay was used to assess the involvement of monooxygenases in resistance development. Sub-species of An. gambiae s.l (An. gambiae and An. coluzzii) were identified using polymerase chain reaction (PCR) and Restriction Fragment Length Polymorphism (PCR-RFLP) while Allele-Specific Polymerase Chain Reaction (AS-PCR) assay was used to detect knockdown mutation (kdr-West; L1014F). Biochemical assays were used in determining the activities of metabolic enzymes. High DDT resistance was recorded in An. coluzzii populations from the three sites. Mortality rate of mosquitoes exposed confirmed Permethrin resistance in Kosofe (50%) and Lagos mainland (48%) but resistance was suspected in Ojo (96%). All specimens tested were confirmed as An. coluzzii with low kdr frequency; 11.6%, 16.4% and 6.7% in Kosofe, Lagos mainland and Ojo respectively. Pre-exposure to synergist (PBO) before exposure to Permethrin led to increased mortality in all populations. Esterase activity was insignificantly overexpressed in Kosofe (p = 0.849) and Lagos mainland (p = 0.229) populations. In contrast, GST activity was significantly lower in populations from Lagos mainland (63.650 ± 9.861; p = 0.007) and Ojo (91.765 ± 4.959; p = 0.042) than Kisumu susceptible strains (120.250 ± 13.972). Monooxygenase activity was higher in Lagos mainland (2.371 ± 0.261) and Ojo (1.361 ± 0.067) populations, albeit significantly in Lagos mainland (p = 0.007) only. Presence of target-site mutation in all populations, increased mortality with pre-exposure to PBO and elevated monooxygenase in Lagos mainland population were confirmed. Multiple resistance mechanisms in some urban populations of An. coluzzii from Lagos, Nigeria calls for appropriate resistance management strategies.
疟疾是非洲主要的公共卫生挑战，尼日利亚在世界上承担着最高的疾病负担。病媒控制已被证明是疟疾控制的一个非常有效的组成部分，然而，主要疟疾病媒昆虫对杀虫剂的抗药性的发展和传播一直是一个主要挑战。本研究评估了来自尼日利亚拉各斯大陆科索费和奥约地方政府地区的按蚊种群的抗药性机制，在这些地区，按蚊属对滴滴涕和氯菊酯有抗药性。采用世界卫生组织（WHO）敏感性生物测定试验来确定按蚊对滴滴涕和氯菊酯的抗药性，同时采用增效剂测定法来评估单加氧酶在抗药性发展中的作用。使用聚合酶链反应（PCR）和限制性片段长度多态性（PCR-RFLP）来鉴定按蚊属的亚种（冈比亚按蚊和按蚊），而等位基因特异性聚合酶链反应（AS-PCR）试验则用于检测击倒突变（kdr-West；L1014F）。生化测定法用于测定代谢酶的活性。来自这三个地点的按蚊种群中记录到了高度的滴滴涕抗性。接触滴滴涕的蚊子死亡率证实了科索费（50%）和拉各斯大陆（48%）的拟除虫菊酯抗性，但奥约（96%）的抗性则存在疑问。所有测试的标本均被确认为按蚊属，其 kdr 频率较低；科索费（11.6%）、拉各斯大陆（16.4%）和奥约（6.7%）。在接触拟除虫菊酯之前预先接触增效剂（PBO）可导致所有种群的死亡率增加。酯酶活性在科索费（p=0.849）和拉各斯大陆（p=0.229）种群中无显著过度表达。相比之下，GST 活性在拉各斯大陆（63.650±9.861；p=0.007）和奥约（91.765±4.959；p=0.042）的种群中显著低于基苏木敏感株（120.250±13.972）。单加氧酶活性在拉各斯大陆（2.371±0.261）和奥约（1.361±0.067）种群中较高，尽管仅在拉各斯大陆种群中具有统计学意义（p=0.007）。所有种群均存在靶标位点突变，用 PBO 预先接触可提高死亡率，并且拉各斯大陆种群中单加氧酶升高，这些均得到了证实。在来自尼日利亚拉各斯的一些城市按蚊种群中存在多种抗药性机制，需要采取适当的抗药性管理策略。
