Resistance to Pyrethroids in the Malaria Vector Anopheles albimanus in Two Important Villages in the Soconusco Region of Chiapas, Mexico, 2022

Abstract

Chiapas State comprises the largest malaria foci from Mexico, and 57% of the autochthonous cases in 2021, all with Plasmodium vivax infections, were reported in this State. Southern Chiapas is at constant risk of cases imported due to migratory human flow. Since chemical control of vector mosquitoes is the main entomological action implemented for the prevention and control of vector-borne diseases, this work aimed to investigate the susceptibility of Anopheles albimanus to insecticides. To this end, mosquitoes were collected in cattle in two villages in southern Chiapas in July–August 2022. Two methods were used to evaluate the susceptibility: the WHO tube bioassay and the CDC bottle bioassay. For the latter, diagnostic concentrations were calculated. The enzymatic resistance mechanisms were also analyzed. CDC diagnostic concentrations were obtained; 0.7 μg/mL deltamethrin, 12 μg/mL permethrin, 14.4 μg/mL malathion, and 2 μg/mL chlorpyrifos. Mosquitoes from Cosalapa and La Victoria were susceptible to organophosphates and to bendiocarb, but resistant to pyrethroids, with mortalities between 89% and 70% (WHO), and 88% and 78% (CDC), for deltamethrin and permethrin, respectively. High esterase levels are suggested as the resistance mechanism involved in the metabolism of pyrethroids in mosquitoes from both villages. Mosquitoes from La Victoria might also involve cytochrome P450. Therefore, organophosphates and carbamates are suggested to currently control An. albimanus. Its use might reduce the frequency of resistance genes to pyrethroids and vector abundance and may impede the transmission of malaria parasites.

Insecticide susceptibility status of Anopheles albimanus populations in historical malaria foci in Quintana Roo, Mexico

“…A recent publication from Solis-Santoyo et al reported An. albimanus populations that were resistant to deltamethrin and permethrin but susceptible to malathion and bendiocarb in two localities in Chiapas State in southern Mexico [ 32 ]. These results differ from the data presented here in two ways.…”

“…First, the entomological collections in Chiapas were conducted in cattle corrals from localities with insecticide pressure derived from livestock and agriculture activities. Second, the diagnostic doses used in the bottle bioassays in the Chiapas study were established using a local reference strain, with insecticide concentrations lower than those recommended by globally recommended protocols [ 32 – 35 ]. National insecticide resistance data for malaria vectors is scarce, highlighting the importance of defining consistent methods for monitoring insecticide susceptibility of anophelines in Mexico.…”