Globally, about 40 species of Anopheles mosquitoes carry malaria. Understanding their biological and behavioral characteristics, as well as effective control methods, is essential for combating and reducing malaria. However, insecticide resistance poses a significant obstacle to controlling these vectors. Organochlorine insecticides have been used to control these vectors for a long time, but resistance, especially of the kdr type, has limited the use of these insecticides.
Four species of An. albimanus, An. darlingi, An. dirus, and An. punctipennis, have caused the spread of malaria in different regions worldwide. The cause of resistance in these vectors has not been widely investigated in the world, and it is unclear whether kdr mutation is the cause of resistance in these vectors. In the following section, kdr mutation was investigated in the mentioned transporters.
Kdr in Anopheles albimanus
An. albimanus is one of the main malaria vectors in various world regions (3). In the past, resistance to organochlorine insecticides, which are widely used to deal with this vector, has been reported. Studies of metabolic mechanisms or insensitivity of the target site, such as mutations in the sodium channel gene (VGSC), have mentioned the cause of this resistance (27, 28). It has been shown that increasing the activity level of esterases and oxidases plays an important role in creating resistance in this vector (29). High oxidase activity and a target site mechanism have also been implicated in cross-resistance between DDT and pyrethroids in An. albimanus (30). Considering the research done on kdr mutation in An. albimanus, only one study has been conducted in Colombia by Orjuela et al. (2019). in which sequencing of all the samples in the forward and reverse direction has been done in the context of three codons of 1010, 1013, and 1014, which are related to resistance to organochlorine insecticides and pyrethroids in malaria vectors. The findings identified the GTT codon at position 1010 (V1010), AAC codon (for asparagine) at position 1013 (N1013), and TTA and TTG codons (for leucine) at position 1014, revealing that no amino acid mutation was observed in the sequences and there is no kdr mutation in them (31). Even though this study has shown that the kdr mutation plays a role in An. Albimanus resistance, it is not resistant to organochlorine insecticides, and more studies are required to confirm this claim.
Kdr in Anopheles darlingi
An. darlingi is one of the vectors of malaria in the world, and it can be found especially in the Amazon region and Africa. This vector has a wide global occurrence and differentiation in genetic, morphological, and behavioral traits, leading to the creation and spread of various insecticide resistance mechanisms (32, 33). For many years, neurotoxic insecticides have been used to deal with this vector. To deal with this vector, it is necessary to evaluate its sensitivity; however, the resistance or sensitivity of this vector has rarely been evaluated so far. Organochlorine insecticides, especially DDT, cause paralysis or death of this transporter by targeting the voltage-gated sodium channel (27, 34). However, kdr mutation has recently been considered. In the study of Orjuela et al. (2019) in Colombia done on An. darlingi, knockdown mutations did not create resistance to organoleptic insecticides. In this study, all samples were analyzed in the forward and reverse direction of sequencing, and three codons, 1010, 1013, and 1014, are related to resistance to organochlorine insecticides and pyrethroids in malaria vectors. The findings identified the GTT codon at position 1010 (V1010), AAC codon (for asparagine) at position 1013 (N1013), and TTA and TTG codons (for leucine) at position 1014, indicating that no amino acid mutation was observed in the sequences and there is no kdr in them (31). Fonseca-González et al. (2009) in Colombia investigated kdr in An. darlingi against organochlorine insecticides and pyrethroids. The findings showed that all populations of An. darlingi were sensitive to deltamethrin, permethrin, and malathion. Resistance to lambda-cyhalothrin and DDT was observed in the population, demonstrating 65 to 75% mortality. Cross-resistance between these two insecticides was also observed. However, specific resistance due to kdr was not observed, and the cause of resistance was reported to be increased metabolism through MFO and NSE (6). Based on the investigated studies, it can be mentioned that kdr mutation has not been observed in An. darlingi, and the cause of resistance in this vector can be metabolic mechanisms and increased activity of oxidases and esterases.
Kdr in Anopheles dirus
An. dirus complex is one of the malaria vectors that can be found in Asia, especially its forest areas. This species has biological and ecological differences and behavioral changes when it is in contact with humans and exposed to environmental stimuli which can improve carrying capacity and environmental adaptation (16, 35, 36). These changes can increase resistance to control measures in this vector. Organochlorine insecticides have been one of the main insecticides used to combat this vector since a long time ago, and the main cause of resistance to these insecticides was reported to be kdr mutation (37). Verhaeghen et al. (2009) investigated kdr in 73 An. dirus mosquitoes in Vietnam. Based on their study, sequencing was performed in the DIIS6 region of the para-type sodium channel gene for the samples to identify kdr, but the results did not show any kdr mutations among the samples (38). Sumarnrote et al. (2017) investigated the kdr mutation in An. dirus against the insecticide deltamethrin in Vietnam. The results of the genetic sequencing of the samples did not show any L1014F or L1014S substitutions in the VGSC gene.
Additionally, the attenuation ratio of this transporter against deltamethrin was 100%, which indicates that it is sensitive to this insecticide (39). In the study by Zeng et al. (2017) in Hainan Province, the attenuation ratio of An. dirus against the insecticides deltamethrin (0.05%), DDT (4%), malathion (5%), and cyfluthrin (0.15%) was 100%, revealing the high sensitivity of this vector against organochlorine insecticides. It should also be mentioned that no kdr mutation was observed in this study (21). In general, kdr mutation has not been detected to create resistance in this vector, and this vector has a high sensitivity to insecticides, including organochlorines.
Kdr in Anopheles Punctipennis
An. punctipennis is a common and widespread malaria vector in the United States and North America (3). This vector can transmit Plasmodium vivax and Plasmodium falciparum [9]. It can also transmit Plasmodium odocoilei to wild animals such as deer, which increases their biodiversity and makes fighting it more complex (40, 41). Also, creating resistance to insecticides in this vector can be another limitation of controlling it. While searching, only one study was found which investigated the kdr mutation in this vector. Orjuela et al. (2019) investigated the kdr mutation in An. punctipennis. The results of sequencing the samples identified the GTT codon at position 1010 (V1010), AAC codon at position 1013 (N1013), and TTA and TTG codons at position 1014. which shows that no amino acid and kdr mutations were observed in the sequences (31). Although this study has shown no kdr mutation in this vector, more studies are needed to confirm this issue.