Mutations in the voltage-gated sodium channel gene of anophelines and their association with resistance to pyrethroids - A review

Constant and extensive use of chemical insecticides has created a selection pressure and favored resistance development in many insect species worldwide. One of the most important pyrethroid resistance mechanisms is classified as target site insensitivity, due to conformational changes in the target site that impair a proper binding of the insecticide molecule. The voltage-gated sodium channel (NaV) is the target of pyrethroids and DDT insecticides, used to control insects of medical, agricultural and veterinary importance, such as anophelines. It has been reported that the presence of a few non-silent point mutations in the NaV gene are associated with pyrethroid resistance, termed as 'kdr' (knockdown resistance) for preventing the knockdown effect of these insecticides. The presence of these mutations, as well as their effects, has been thoroughly studied in Anopheles mosquitoes. So far, kdr mutations have already been detected in at least 13 species (Anopheles gambiae, Anopheles arabiensis, Anopheles sinensis, Anopheles stephensi, Anopheles subpictus, Anopheles sacharovi, Anopheles culicifacies, Anopheles sundaicus, Anopheles aconitus, Anopheles vagus, Anopheles paraliae, Anopheles peditaeniatus and Anopheles albimanus) from populations of African, Asian and, more recently, American continents. Seven mutational variants (L1014F, L1014S, L1014C, L1014W, N1013S, N1575Y and V1010L) were described, with the highest prevalence of L1014F, which occurs at the 1014 site in NaV IIS6 domain. The increase of frequency and distribution of kdr mutations clearly shows the importance of this mechanism in the process of pyrethroid resistance. In this sense, several species-specific and highly sensitive methods have been designed in order to genotype individual mosquitoes for kdr in large scale, which may serve as important tolls for monitoring the dynamics of pyrethroid resistance in natural populations. We also briefly discuss investigations concerning the course of Plasmodium infection in kdr individuals. Considering the limitation of insecticides available for employment in public health campaigns and the absence of a vaccine able to brake the life cycle of the malaria parasites, the use of pyrethroids is likely to remain as the main strategy against mosquitoes by either indoor residual spraying (IR) and insecticide treated nets (ITN). Therefore, monitoring insecticide resistance programs is a crucial need in malaria endemic countries. © 2014 Silva et al.; licensee BioMed Central Ltd

Isolation and characterization of polymorphic DNA microsatellite loci for Anopheles triannulatus sensu lato (Diptera: Culicidae) and cross-amplification in congeneric species

Anopheles (Nyssorhynchus) triannulatus is a complex of 3 species. Thirteen polymorphic microsatellite loci were isolated and characterized in 20 to 25 individuals from Manaus (AM, Brazil). The number of alleles per locus varied from 3 to 10 (mean = 6.0). The observed heterozygosity ranged from 0.250 to 0.875 (mean = 0.680) and expected heterozygosity ranged from 0.376 to 0.844 (mean = 0.698). Two loci exhibited null alleles and all loci were in Hardy-Weinberg equilibrium. No linkage disequilibrium between loci was observed. These loci were used in 4 congeneric species and provide a useful tool for studying population genetics and other aspects of the biology of this and other Anopheles species. ©FUNPEC-RP

Isolation and characterization of 25 microsatellite DNA loci for Anopheles albitarsis sensu lato and inter-specific amplification in 5 congeneric species.

The Anopheles albitasis complex includes 6 species, and 3 are considered as malaria vectors in Brazil. Twenty-five polymorphic microsatellite DNA loci were isolated and characterized in 24-36 individuals from the neighborhood of Puraquequara, Manaus, Amazonas State, Brazil. The number of estimated alleles ranged from 2 to 10, the observed heterozygosity ranged from 0.182 to 0.897, and the expected heterozygosity ranged from 0.260 to 0.854. Eleven loci showed significant deviation from Hardy-Weinberg equilibrium. Eleven loci were cross-amplified successfully in 5 Anopheles species. These microsatellite loci will be useful in studies investigating population structure and evolutionary genetics in A. albitarsis sensu lato and other A. albitarsis complex species

Differentiation and genetic variability in natural populations of Anopheles (N.) triannulatus (Neiva & Pinto, 1922) of Brazilian Amazonia.

Populations of Anopheles triannulatus from Macapá (AP), Aripuanã (MT), Ji-Paraná (RO), and Manaus-Janauari Lake (AM) were studied using 16 enzymatic loci. The results of the isozyme analysis showed that the population of Macapá presented higher polymorphism (56.3%). The lowest variability was observed in the population of Manaus (p = 25.0; Ho = 0.077 +/- 0.046). The results of Wright's F statistics showed unbalance due to excess of homozygotes (F(is) > F(st)), denoting a certain intrapopulational differentiation. Although the populations are genetically very close (D = 0.003-0.052), the dendrogram separates the populations in two groups: Macapá separated from that of Manaus, Ji-Paraná, and Aripuanã. This result may suggest a reduction in the genic flow, which possibly had some influence in the substructuration of the populations

Mutations in the voltage-gated sodium channel gene of anophelines and their association with resistance to pyrethroids – a review

Constant and extensive use of chemical insecticides has created a selection pressure and favored resistance development in many insect species worldwide. One of the most important pyrethroid resistance mechanisms is classified as target site insensitivity, due to conformational changes in the target site that impair a proper binding of the insecticide molecule. The voltage-gated sodium channel (NaV) is the target of pyrethroids and DDT insecticides, used to control insects of medical, agricultural and veterinary importance, such as anophelines. It has been reported that the presence of a few non-silent point mutations in the NaV gene are associated with pyrethroid resistance, termed as ‘kdr’ (knockdown resistance) for preventing the knockdown effect of these insecticides. The presence of these mutations, as well as their effects, has been thoroughly studied in Anopheles mosquitoes. So far, kdr mutations have already been detected in at least 13 species (Anopheles gambiae, Anopheles arabiensis, Anopheles sinensis, Anopheles stephensi, Anopheles subpictus, Anopheles sacharovi, Anopheles culicifacies, Anopheles sundaicus, Anopheles aconitus, Anopheles vagus, Anopheles paraliae, Anopheles peditaeniatus and Anopheles albimanus) from populations of African, Asian and, more recently, American continents. Seven mutational variants (L1014F, L1014S, L1014C, L1014W, N1013S, N1575Y and V1010L) were described, with the highest prevalence of L1014F, which occurs at the 1014 site in NaV IIS6 domain. The increase of frequency and distribution of kdr mutations clearly shows the importance of this mechanism in the process of pyrethroid resistance. In this sense, several species-specific and highly sensitive methods have been designed in order to genotype individual mosquitoes for kdr in large scale, which may serve as important tolls for monitoring the dynamics of pyrethroid resistance in natural populations. We also briefly discuss investigations concerning the course of Plasmodium infection in kdr individuals. Considering the limitation of insecticides available for employment in public health campaigns and the absence of a vaccine able to brake the life cycle of the malaria parasites, the use of pyrethroids is likely to remain as the main strategy against mosquitoes by either indoor residual spraying (IR) and insecticide treated nets (ITN). Therefore, monitoring insecticide resistance programs is a crucial need in malaria endemic countries