Nationwide integrative analysis of pyrethroid resistance in Aedes aegypti from Mexico

Aedes aegypti, the primary vector of dengue, Zika, and chikungunya in Mexico, has developed resistance to pyrethroids due to their prolonged and widespread use. Resistance is mainly associated with knockdown resistance (kdr) target-site mutations in the voltage-gated sodium channel (VGSC) gene and increased detoxification by metabolic resistance enzymes. However, nationwide data on resistance distribution and associated resistance mechanisms remain limited. In this study, we conducted a nationwide assessment of pyrethroid resistance in Ae. aegypti from Mexico. Phenotypic resistance to permethrin and deltamethrin was evaluated using CDC bottle bioassays. The frequency of three kdr mutations (V410L, V1016I, and F1534C) was determined by allele-specific PCR, and multilocus genotypes were analyzed to explore associations with survival after insecticide exposure. Additionally, enzyme activity levels of α-/β-esterases, cytochrome P450 monooxygenases (P450s), and glutathione S-transferases (GSTs) were quantified. Most populations exhibited low mortality, confirming widespread resistance to permethrin across all regions and to deltamethrin in the majority populations. The lowest mortalities were concentrated in populations from the Gulf and southern localities, while some Pacific populations remained susceptible to deltamethrin. The grouped multilocus genotype LIC was the most prevalent nationwide, with VL/VI/CC as the dominant haplotype, followed by the triple homozygote mutant LL/II/CC. LIC was significantly associated with survival after permethrin exposure (OR = 0.21, 95 % CI: 0.14-0.30, p < 0.0001). Elevated P450 activity was consistently observed in resistant populations, supporting its role in metabolic mechanisms. While α- and β-esterase and GST activities were elevated in some populations, only P450 showed consistent increases. This nationwide analysis highlights the broad geographic distribution and complexity of pyrethroid resistance in Ae. aegypti from Mexico, providing critical evidence to support informed resistance monitoring and the urgent implementation of effective vector control strategies.