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Poster Session

Poster Session

P-4 - Insecticide Resistance in Anopheles (Nyssorhynchus) darlingi Populations from Barcelos, Brazilian Amazon: Implications for Malaria Vector Control

Wednesday, March 5, 2025
12:15 PM – 1:45 PM AST
Location: Hall A
Abstract: Limited data exist on insecticide resistance in Anopheles populations in Brazil. Barcelos, a city in the Amazonas state endemic for malaria, focuses its antimalarial strategies on vector control, involving extensive use of pyrethroid insecticides.

Objective: We assessed the susceptibility and resistance mechanisms in Anopheles darlingi populations from Barcelos´ urban area to the pyrethroids deltamethrin_DEL, etofenprox_ETF, and alpha-cypermethrin_ACP, as well as the neonicotinoid clothianidin (SumiShield®50WG_SS) developed for indoor residual spraying in regions with vectors resistant to other insecticide classes.

Methods: In August 2024, standard insecticide tube bioassays_WHO were conducted in the field and at Fiocruz laboratory using F1 An. darlingi female derived from Barcelos specimens. Three bioassays were performed for each pyrethroid (DEL, ETF, ACP) in laboratory and three field bioassays were conducted with DEL, using the WHO discriminative doses(DD): DEL-0.05%; ETF-0.5%; ACP-0.05%. knockdown(kd) effect at 1h, time for 50% knockdown (kdt50), and mosquito mortality after 24h of recovery were evaluated. Regarding SumiShield®50WG (DD 3.5% for An. darlingi determined through previous dose-response bioassays), mortality was assessed after 1h of exposure, and after 24, 48, and 72h of recovery. Resistance status was classified based on mortality as "susceptible"(≥98%), "possible resistance"(90 to < 98%), "confirmed resistance"(0 to < 90%). Additionally, Genetic (kdr mutation) and metabolic resistance mechanisms (synergist-insecticide bioassays with PBO4%) were evaluated.

Results: Pyrethroids mortality rates were: a)Field tests with DEL=78.3% (kdt50=1h; kd=56.6%); b)Laboratory tests: DEL=58.3% (kd=26.8%; kdt50 >24h), ETF=44.4±26.2% (kd=16.8±6.4%; kdt50 >24h); ACP=26.6±14.2% (kd=8.4±5.1%; kdt50 >24h). SumiShield®50WG mortality rates were: 1h=5%; 24h=85%; 48h=100%. No kdr mutations were detected. Complete restoration of susceptibility to pyrethroids (100% mortality within 1h) following PBO exposure, suggesting a monooxygenase-mediated resistance mechanism.

Conclusion: Metabolic resistance to pyrethroids is present in An. darlingi populations from Barcelos, posing a challenge to current vector control strategies. SumiShield®50WG showed efficacy but with delayed action, requiring further evaluation of its practical utility.