Bioefficacy of cyfluthrin (SOLFAC EW050) impregnated bed-nets against Anopheles gambiae in southern Cameroon.

The bioefficacy of cyfluthrin-impregnated bed-nets was evaluated in the agro-industrial town of Mbandjock (southern Cameroon). The objectives were to assess the knockdown and mortality rates, the protection against bloodfeeding mosquitoes, and the irritant effect of cyfluthrin (SOLFAC EW050)-impregnated bed-nets against a susceptible strain of Anopheles gambiae. Polyester bed-nets were impregnated and distributed to inhabitants of Mbandjock for use, then nets were retreated after 6 months. The uptake of active ingredient on nets ranged from 30.8 mg/m2 to 75.1 mg/m2 at the initial treatment and from 131.0 mg/m2 to 225.0 mg/m2 at retreatment. The susceptible Kisumu reference strain of Anopheles gambiae reared in our laboratory was used for bioassays. The knockdown rate on freshly treated nets (2 wk after treatment) ranged from 93 to 96% and the mortality rate ranged from 52 to 70%. During the 12-month trial, knockdown and mortality rates showed 2 peaks, respectively, in the 4th month (94-97% knockdown and 61-96% mortality) and 7th month (i.e., soon after retreatment; 89-98% knockdown and 86-100% mortality), separated by breakdowns on the 5th through 6th and 12th months (46-77% knockdown and 8-69% mortality). Knockdown and mortality rates decreased faster on the lower part of nets than on the top, suggesting that some external factors such as dirt and daily hand manipulation could impede the efficacy of treated nets. Exceedingly dirty nets were less effective than clean nets. The protective rate against bloodfeeding mosquitoes ranged from 60 to 100% during the 1st 4 months and decreased at 40-70% during the 5th and 6th months after the initial treatment. After retreatment, the protective rate ranged from 50 to 90% for the 1st 5 months and from 35 to 64% at the 6th month. More than 70% of mosquitoes that attempt to feed through treated or retreated nettings died within 24 h after contact. Cyfluthrin was found to be mildly irritant during the whole evaluation. This trial reveals that cyfluthrin EW050-treated nets were effective against a susceptible strain of An. gambiae.