Indoor Residual Spraying

Indoor residual spraying (IRS) is the application of insecticide to the inside of dwellings, on walls and other surfaces that serve as a resting place for malaria-infected mosquitoes. IRS kills mosquitoes when they come in contact with treated surfaces, preventing disease transmission. 

For IRS to be effective, the following conditions must apply:

  1. Majority of vectors (i.e., organisms that transmit malaria) must feed and rest indoors
  2. Vectors are susceptible to the insecticide in use
  3. Houses have “sprayable” surfaces  
  4. A high proportion of the houses in target areas are sprayed (more than 80 percent).

History of IRS

Large-scale IRS with DDT for malaria control started in 1946.  Early DDT spraying campaigns were effective in killing mosquitoes that transmit malaria. Impressed with the results of these programs, the World Health Organization (WHO) and other international organizations launched the Malaria Eradication Program in 1955. IRS and chloroquine treatment were the primary malaria control interventions from 1955-1969.

Most African countries were not involved in the eradication campaign; however, several countries began pilot projects of IRS with DDT between the 1940s and 1960s. Malaria was considerably reduced though it was not interrupted as a result of these efforts. 

The environmental and human safety of DDT was challenged following the publication of the book Silent Spring by Rachel Carson in 1962. In addition to environmental concerns, mosquitoes eventually became resistant to DDT.  By 1969, the eradication campaign ended, having eliminated malaria from areas where about 700 million people lived.

Since the eradication era, IRS has successfully been implemented in several Southern African countries (Mozambique, South Africa, Swaziland, and Zimbabwe) and in countries where malaria is highly seasonal (Eritrea, Ethiopia, and Madagascar).

Today PMI, The Global Fund for HIV/AIDS Tuberculosis and Malaria, The World Bank Global Strategy & Booster Program, and other malaria partners are supporting IRS activities in vulnerable countries.  In 2010, 185 million people were protected with IRS globally, of which nearly half live in Africa.

1 World Malaria report 2011