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Indoor residual spraying for mosquito control – the importance of training spray operators

| July 3, 2016
Using a stick attached to the spray lance as a guide to indicate distance to the wall.

Using a stick attached to the spray lance as a guide to indicate distance to the wall.

Indoor residual spraying (IRS) with DDT began in the 1940’s in Sardinia where full-scale operations were carried out to control Anopheles labranchiae to control malaria. In the Italian campaign, the number of cases of malaria fell from 78,173 in 1944 to 44 in 1950. This led to WHO launching a Global Malaria Eradication Programme in 1955, which was most successful in Europe and North America. The programme was not sustained elsewhere and suffered technical problems, such as mosquitoes becoming resistant to DDT.

Subsequently, as malaria vectors usually bite predominantly at night, between 2200 hrs and 0500 hrs, emphasis since the late 1980’s has been on using bed nets treated with a pyrethroid insecticide. Mosquitoes, attracted by a person sleeping under a net, pick up a lethal dose on coming in contact with such nets, and they also provide a physical barrier. Insecticide treated nets have been particularly effective in reducing the death of young children and reducing morbidity. Much of the reduction in malaria deaths and cases during the last 10 years is attributable to the use of long-lasting insecticidal nets, coated with or incorporating a pyrethroid.

However, the long persistence of insecticide in treated nets has again resulted in mosquitoes becoming resistant to pyrethroid insecticides, so attention is again being given to Indoor residual spraying (IRS) as a supplementary measure, as insecticides with alternative modes of action, that can be applied to walls, have become available. In areas with a single rainfall season, persistence of insecticidal deposits on indoor surfaces need not exceed 5-6 months and would usually require a single round of spraying depending upon the type of formulation.

The campaigns to implement IRS have depended on training teams of temporary staff to apply the insecticides to walls of houses using a manually carried compression sprayer. In Africa, for example, this has been possible with USAID funds, largely due to the President’s Malaria Initiative (PMI) programme. The technique used is based on the WHO Manual for Indoor Residual Spraying, and the specifications for equipment were originally published in 1964.

This is an extract of the full article published in International Pest Control – March/April 2016 issue.

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Authors: Graham Matthews* and Rajpal Yadav**
*IPARC, Imperial College  ** WHO

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Category: Public health