Suppression of exposure to malaria vectors by an order of magnitude using microbial larvicides in rural Kenya

Abstract

To determine the contribution larviciding could make to reduce the burden of malaria, by conducting a trial of microbial larvicides in a 4.5 km2 area in and around a large village in rural western Kenya. The abundance of immature and adult mosquitoes was monitored for 12 months under baseline conditions. Then microbial larval control was implemented for 28 months. After the intervention, the abundance of immature and adult mosquitoes was monitored for a further 12 months. Of the 419 mosquito larval habitats identified, 336 (80%) originated from human activities. Application of Bacillus thuringiensis var. israelensis and Bacillus sphaericus larvicides reduced the proportion of aquatic habitats containing Anopheles larvae from 51% during non-intervention periods to 7% during the intervention. The occurrence of late instar Anopheles in habitats was reduced from 39% and 33% in pre-intervention and post-intervention periods to 0.6% during intervention. Overall, larviciding reduced Anopheles larval density by 95% and human exposure to bites from adults by 92%. The estimated cost of providing this protection to the human population in the study area was less than US$ 0.90/person/year. Appropriately applied microbial larvicides can substantially and cost-effectively reduce human exposure to malaria in rural sub-Saharan Africa.