Evaluation of a longer lasting insecticide formulation for Indoor Residual Spraying: Uganda
Situation:
Indoor Residual Spraying (IRS) is an effective means of malaria control in some settings. IRS involves spraying the indoor walls and ceilings of houses with an appropriate insecticide. Mosquitoes entering a house to feed rest on the walls and pick up a lethal dose of an insecticide. This means that few mosquitoes in that areas will live to old age (in mosquito terms about 12 days or more). Only mosquitoes that live that long can transmit malaria as the parasite must undergo development in the mosquito body. With IRS and no older mosquitoes, malaria transmission is dramatically reduced.
In practice, the effectiveness of IRS depends on many factors including high quality and high coverage of spraying which in turn depend on public acceptance of spraying, the availability of well-maintained equipment, adequately trained spraying personnel, efficient supervision and strong financial support. The size of the operational area depends on local circumstances and is influenced by the distribution of malaria and malaria vectors, the distance from important breeding sites, the flight range of the vectors and demographic features.
The profile of indoor residual spraying as a control strategy has been raised in recent years through political commitment to this intervention. One of the key discussions is over the use of the longer-acting DDT as opposed to the pyrethroid insecticides.
Response:
The Malaria Consortium is carrying out a trial of a new formulation of a pyrethroid insecticide (developed by Syngenta) in a peri-urban area outside Kampala. We hope this formulation will last 3-4 times longer than current formulations, making it a more realistic alternative to DDT. This is a small scale study examining the residual life of lambdacyhalothrin CS (Icon CS) in two doses, 25 mg/m2 and 50 mg/m2 on 80 houses of three different wall types - mud, plain plaster or painted plaster walls. Icon CS is a pyrethroid insecticide with very low toxicity to humans. The residual life of the insecticide will be monitored over a 12 month period using contact bioassays on the walls of the house.
Points to Note:
Once the residual life of Icon CS on these different surfaces is known it will be possible to revisit the insecticide options for IRS spraying and address the issues of cost comparison between DDT and pyrethroid insecticides. It is likely with a longer lasting pyrethroid that the cost difference between these options is minimal, or in favour of pyrethroids Discussions are underway to expand the trial and include a comparison with DDT.
For more information from Syngenta click here
Photo: Malaria Consortium