Indoor Residual Spraying
Indoor Residual Spraying (IRS) is a standardised and well-established control method for mosquitoes. It has been used widely in Asia, the Pacific and Latin America, while in Africa its use has been more limited to the margins of malaria distribution in southern Africa and to epidemic-prone countries often at higher altitudes. WHO has recently proposed extending its range in Africa.
IRS can kill a mosquito any time it enters a house for a blood meal, which it typically does every 2-3 days, so that few will survive the approximately 12 days that are required for malaria parasites to complete part of their life cycle in the vector mosquito, if all the houses they visit are properly sprayed. In practice, the effectiveness of IRS depends on adherence to application procedure, efficacy of the insecticide, public acceptance of spraying, 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.
Generally all internal walls and ceilings of the building are treated. Residual effects depend on porosity of the surface (shorter on mud walls) and exposure to sunlight. Four classes of chemical insecticides-organochlorines, organophosphates, carbamates and pyrethroids-are still the mainstay of vector control programmes. Use of pyrethroid insecticides has, however, increased, and that of the organochlorines and some of the more toxic organophosphate compounds has decreased in recent years. The continued use of DDT for disease vector control is conditionally approved under the Stockholm Convention on Persistent Organic Pollutants, in accordance with WHO recommendations and guidelines, and when locally safe, effective and affordable alternatives are not available. Selection depends on cost, efficacy and availability. Water-dispersible powders are generally used, applied with a hand operated pressurised sprayer. Frequency of spraying will vary from once to twice yearly according to seasonality of vector breeding, transmission of malaria and residual effect of insecticide.
Key Points:• Spraying with a residual insecticide inside houses and buildings can provide highly effective control of malaria.
• It requires well trained and supervised personnel and well maintained high quality spraying equipment.
• Several insecticides can be used as water based compounds.
• Frequency of spraying depends on seasonality of malaria transmission, building materials and insecticide residual effect.
• The selection of IRS as a control strategy needs to be based on local assessment of malaria risk and programme capacity.
The Malaria Consortium is presently conducting an evaluation of IRS using new formulations of insecticide in Uganda. This is a small scale study examining the residual life of lambdacyhalothrin CS (Lambda CS) in two doses, 25 mg/m2 and 50 mg/m2 on 60 houses of three different wall types - mud, brick or plaster and paint - supported by Syngenta Professional Products. Lambda CS is a pyrethroid insectide with very low toxicity to humans. The residual life of the insecticide will be monitored over a 12 month period using light traps to look at mosquito numbers entering houses and by contact bioassays on the walls of the house.
References* WHO (2006) Indoor Residual Spraying. Use of indoor residual spraying for scaling up global malaria control and elimination. WHO/HTM/MAL/2006.1112
* Conteh, L., Sharp, B.L., Streat, E., Barreto, A & Konar, S. (2004) The cost and cost-effectiveness of malaria vector control by residual insecticide house-spraying in southern Mozambique: a rural and urban analysis. Tropical Medicine & International Health 9 (1): 125-132.
* Curtis, C. & Mnzava, A.E.P. (2000) Comparison of house spraying and insecticide treated nets for malaria control. Bulletin of the World Health Organization, 78: 1389-1400.
* Guyatt, H.L., Corlett, S.K., Robinson, T.P., Ochola, S.A. & Snow, R.W. (2002) Malaria prevention in highland Kenya: indoor residual house-spraying vs. insecticide-treated bednets. Tropical Medicine and International Health 7: 298-303.
* WHO (2006) Pesticides and their application. Department of Control of Neglected Tropical Diseases, WHO Pesticide evaluation scheme (WHOPES) WHO/CDS/NTD/WHOPES/GCDPP/2006.1
* WHO (2002) Manual for Indoor Residual Spraying. Department of Control of Neglected Tropical Diseases, WHO Pesticide evaluation scheme (WHOPES) WHO/CDS/WHOPES/GCDPP/2000.3 Rev.1
* WHO (2005) Ten things you need to know about DDT use under the Stockholm Convention. WHO/HTM/RBM/2004.55 rev. 1
* Guyatt, H.L., Kinnear, J., Burrini, M. & Snow, R.W. (2002) A comparative cost of insecticide treated nets and indoor residual spraying in Highland Kenya. Health Policy and Planning 17(2): 144-153.
* Rozendaal, J.A. (1997) Vector control: methods for use by individuals and communitites. Chapter 9: House Spraying with Residual Insecticides. WHO
* Rozendaal, J.A. (1997) Vector control: methods for use by individuals and communitites. Chapter 10: Safe Use of Pesticides, WHO
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