Characterization and monitoring of deltamethrin‑resistance in Anopheles culicifacies in the presence of a long‑lasting insecticide‑treated net intervention

Abstract

Background: Deltamethrin-impregnated, long-lasting insecticidal nets (LLINs) were distributed in the study area

from November 2014 to January 2015 to evaluate their impact on malaria transmission in the presence of insecticideresistant

vectors. Studies were carried out in 16 selected clusters in Keshkal sub-district, Chhattisgarh State, India to

monitor and characterize deltamethrin resistance in Anopheles culicifacies sensu lato.

Results: Deltamethrin susceptibility of An. culicifacies decreased in a post-LLIN survey compared to a pre-LLIN survey

and was not significant (p > 0.05) while, the knockdown values showed significant increase (p < 0.05). Pre-exposure

to piperonyl butoxide, triphenyl phosphate showed synergism against deltamethrin (p < 0.001). Biochemical assays

showed significantly (p < 0.05) elevated monooxygenases in 3 of 5 clusters in post-LLIN survey-I that increased to 10

of 11 clusters in post-LLIN survey-II, while esterases were found significantly elevated in all clusters and both enzymes

were involved in conferring pyrethroid resistance, not discounting the involvement of kdr (L1014L/S) gene that was

heterozygous and at low frequency (4–5%).

Conclusion: This field study, in a tribal district of India, after distribution of deltamethrin-impregnated LLINs showed

decrease in deltamethrin susceptibility in An. culicifacies, a major vector of malaria in this study area and in India.

Results indicated development of resistance as imminent with the increase in insecticide selection pressure. There is

an urgent need to develop new vector control tools, with insecticide classes having novel mechanisms of resistance,

to avoid or delay the onset of resistance. Regular insecticide resistance monitoring and mechanistic studies should

be the priority for the malaria control programmes to suggest strategies for insecticide resistance management. The

global commitment to eliminate malaria by 2030 needs various efforts that include development of combination vector

control products and interventions and few are becoming available.