Indoor residual spraying

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Indoor residual spraying is the process of spraying the inside of dwellings with a pesticide to kill mosquitoes that spread malaria. In the last 30 years, the practice has been controversial. Some authorities called it useless or disparaged its use as counterproductive or expensive, compared to bed nets, prophylactic tablets or simply treating the disease after infection occurs.[attribution needed] Others said that when properly applied it can save lives and reduce malaria mortality from an epidemic to minor risk.[attribution needed]

A solution of pesticide is sprayed by a specially-equipped, trained worker, on the inside walls of certain types of dwellings. The walls must be porous, such as mud or wood - not plaster as in city dwellings. One application works for 6 months or 1 year. The mosquitoes are either repelled or killed by the pesticide.

According to the World Health Organization's position paper on IRS:[1]

WHO recommends that national governments should:

  1. Introduce and/or scale up coverage of targeted IRS as a primary malaria control intervention in countries where available data indicates that it can be effective towards achieving malaria targets.
  2. Take all necessary steps to ensure effective implementation of IRS interventions, including selecting the appropriate insecticide, spraying where and when necessary and sustaining a high level of coverage, and to prevent unauthorized or un-recommended use of public health insecticides.
  3. Strengthen the managerial capacity of national malaria control programmes and improve human, technical and financial resources for the timely delivery and high coverage of effective interventions including IRS, with adequate

monitoring and evaluation.

The WHO recommeds the following insecticides for IRS[2]:

Insecticide Class Recommended dosage of active ingredient (g/m2) Duration of effective action (months) Estimated cost per house pewr 6 months (US$)[3] WHO toxicity rating[4]
DDT Organochlorine 1–2 >6 1.60 II
Fenitrothion Organophosphate 2 3–6 14.80 II
Malathion Organophosphate 2 2–3 8.20 III
Pirimiphos-methyl Organophosphate 1–2 2–3 III
Propoxur Carbamate 1–2 3–6 18.80 II
Bendiocarb Carbamate 0.1–0.4 2–6 13.80 II
Alpha-cypermethrin Pyrethroid 0.02–0.03 4–6 II
Cyfluthrin Pyrethroid 0.02–0.05 3–6 II
Deltamethrin Pyrethroid 0.02–0.025 3–6 1.60 II
Etofenprox Pyrethroid 0.1–0.3 3–6 U
Lambda-cyhalothrin Pyrethroid 0.02–0.03 3–6 8.60 III
Bifenthrin Pyrethroid 0.025–0.05 3–6 II

Finally, in choosing an insectide for IRS, the WHO states the following factors must be considered:[1]

  1. insecticide susceptibility and vector behaviour;
  2. safety for humans and the environment;
  3. efficacy and cost-effectiveness.


  1. 1.0 1.1 Indoor Residual Spraying: Use of Indoor Residual Spraying for Scaling Up Global Malaria Control and Elimination. World Health Organization, 2006.
  2. Sadasivaiah, Shobha; Tozan, Yesim; Breman, Joel G. (2007), "Dichlorodiphenyltrichloroethane (DDT) for Indoor Residual Spraying in Africa: How Can It Be Used for Malaria Control?", Am. J. Trop. Med. Hyg., 77 (Suppl 6): 249–263
  3. "Excluding operational costs and freight and other external costs"
  4. Ia = Extremely Hazardous; Ib = Highly Hazardous; II = Moderately Hazardous; III = Slightly Hazardous; U = Unlikely To Be Hazardous. Source: World Health Organization, The WHO Recommended Classification of Pesticides by Hazard, 2005.