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A new strategy for treating nets. Part 1: formulation and dosage.
J E Miller1, A Buriyo, A Karugila
1Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, UK.
Summary
Frequent washing of insecticide-treated nets (ITNs) requires adjusted pyrethroid dosages. A low-dose, frequent-retreatment system using water-based formulations proved effective for mosquito control, even with repeated washing.
Area of Science:
- Medical Entomology
- Insecticide Resistance Management
- Public Health Entomology
Background:
- Conventional pyrethroid insecticide dosages on mosquito nets assume infrequent retreatment (6-12 months).
- Net washing frequency significantly impacts insecticide requirements and efficacy.
- Water-based pyrethroid formulations are preferable for domestic use over emulsifiable concentrates (ECs).
Purpose of the Study:
- To evaluate the efficacy of different pyrethroid formulations and retreatment strategies for insecticide-treated nets (ITNs).
- To determine optimal pyrethroid dosages and retreatment intervals based on net washing frequency.
- To compare water-based formulations with traditional emulsifiable concentrates (ECs) for mosquito control.
Main Methods:
- Laboratory bioassays using Anopheles gambiae to test insecticidal activity of three pyrethroids (deltamethrin, lambdacyhalothrin, permethrin) in EC, Flowable, and CS formulations.
- Gas chromatography analysis of pyrethroid accumulation on nets after repeated washing and retreatment cycles.
- Experimental hut trials comparing different net retreatment regimes (low-dose frequent-wash vs. high-dose infrequent-wash) against untreated nets.
Main Results:
- Water-based pyrethroid formulations demonstrated comparable or superior efficacy to ECs, even at low dosages.
- Pyrethroid levels on nets rapidly accumulated and stabilized with frequent wash-retreatment cycles, maintaining high insecticidal activity.
- Nets subjected to a high initial dose followed by low-dose retreatment maintained high mortality rates against Anopheles females throughout the experiment.
Conclusions:
- A 'low-dose, frequent-wash' retreatment strategy is technically appropriate and potentially more affordable for frequently washed nets.
- High initial 'loading' doses with subsequent lower 'maintenance' doses for retreatment are recommended for sustained insecticidal benefits.
- Water-based pyrethroid formulations are effective and suitable alternatives to ECs for ITN applications.