Multiple mechanisms of resistance to pyrethroids in Anopheles gambiae s.l populations in Niger.

INTRODUCTION: We performed a transversal study to map resistance of malaria vectors (Anopheles mosquitoes) to insecticides in Niger within the frame of the National Malaria Control Program funded by the World Health Organization (WHO).

METHOD: Larvae of Anopheles gambiae s.l were collected from November to December 2013 in seven locations selected on the basis of different patterns of use of insecticides and environment. WHO susceptibility test tubes were used on females Anopheles to detect resistance to insecticides. Eight insecticides were tested. Percentages of knockdown during exposure time to pyrethroids and DDT and mortality after 24hours of observation for all tested insecticides were calculated. PCR and biochemical tests were carried out to identify the species and mechanisms of resistance (Kdr allele frequencies and activity of detoxification enzymes).

RESULTS: In all sites, Anopheles gambiae s.l was susceptible to bendiocarb and malathion but resistant to the five pyrethroids and DDT (24-hour mortality rate was <90%). The Kdr mutation was present in the molecular form M of Anopheles gambiae with an average frequency of 58%. Biochemical tests showed the activity of various enzyme families (esterase, oxidase, and glutathione s-transferase).

CONCLUSION: This study showed multiple resistance of Anopheles mosquitoes to insecticides in Niger. A rigorous management of this resistance is imperative to preserve the efficacy of pyrethroids as it is the only class of insecticides used for insecticide-treated nets.