Performance evaluation of chemical insecticides used for indoor residual spraying against Anopheles arabiensis in Ethiopia

Abstract

Introduction: Monitoring of the residual efficacy of insecticides is essential to determine the periods that they remain effective in interrupting malaria transmission and schedule when to re-spray. There is a critical need to establish evidence-based information for the insecticide (s) that would be used for IRS in Ethiopia. Objectives: (1) To assess the Indoor Residual Spray quality on different wall surfaces, (2) To determine the residual efficacy of Bendiocarb 80% WP, Propoxur 50% WP and Actellic 300 CS sprayed on different wall surfaces against An. arabiensis, (3) To estimate the decay rate of Bendiocarb 80% WP, Propoxur 50 % WP and Actellic 300 CS sprayed on different wall surfaces, and (4) To evaluate the community acceptability of the Indoor Residual Spray.

Materials and Methods: The study employed both cross-sectional (assessment of quality of spray) and longitudinal monitoring of the residual efficacy of chemical insecticides on different wall surfaces of sprayed houses in purposively selected villages. In Wondo Genet 48 test houses and 4 control houses were selected for the study. Similarly, 36 test houses and 3 control houses were used for the Mirab Abaya study. Each insecticide treatment was carried out in 12 houses for each wall type on the condition that all wall types were present in each study village. This means that an insecticide was sprayed in 48 and 36 houses respectively where the wall types were rough, smooth, cement and painted. The concentration of the insecticides was assessed by High Performance Liquid Chromatography.

Results:  

The first, second, third and fourth rounds test results summarized as follows. The overall mosquito mortality exposed to wall surfaces sprayed with Propoxur 50% WP ranged from 82.5% - 100% and 91% - 100% for Wondo Genet and Mirab Abaya sites, respectively. The overall mosquito mortality exposed to wall surfaces sprayed with Bendiocarb 80% WP ranged from 85.4% - 100% and 91.1% - 100% for Wondo Genet and Mirab Abaya sites, respectively. The overall mosquito mortality exposed to wall surfaces sprayed with Actellic 300 CS ranged from 96.9% -100% and 94.8% - 100% for Wondo Genet and Mirab Abaya sites, respectively. .. At round five of the assessment, mosquito mortality from Actellic 300 CS sprayed wall surfaces was 84.4% and 87% for Mirab Abaya and Wondo sites, respectively. During the six round residual efficacies monitoring mosquito mortality was found to drop to 52.2% and 48.3% for the two sites, respectively, which is below the required WHO cutoff (point ≥ 80%). The effect of Bendiocarb 80% WP on mosquitoes’ mortality was found below the WHO cutoff value during the fifth and sixth round monitoring (51.5% for Mirab Abaya site in the sixth round, and 70.9% then 41.25% for Wondo Genet sites in the fifth and sixth round monitoring, respectively) with exception in the fifth round for Mirab Abaya sites (84.1%). The performance of Propoxur 50% WP was below the required WHO value for both sites in the fifth and sixth round monitoring (78.2% and 77.4% in the fifth round, and 50.3% and 41.4% in the sixth round for Mirab Abaya and Wondo Genet sites, respectively). The performance of the Propoxur 50% WP, Bendiocarb 80% WP and Actellic 300 CS on rough, smooth, cement and painted wall surfaces was similar up to the third-round monitoring. Differences in performance were observed at fourth and fifth round monitoring. With regard to acceptability of Indoor Residual Spray, 90.5% of the respondents in Wondo Genet site agreed to allow house spraying in the future and. (100% of the respondents in Mirab Abaya site agreed to allow IRS for malaria and other vector borne diseases protection.

Conclusion: The performances of Actellic 300 CS and Bendiocarb 80% WP were better in smooth, cement and painted wall surfaces than the rough wall surface types which is found within the WHO recommendation limit. For drawing further conclusions similar studies are recommended in other sites by different partners in a collaborative and coordinated manner.