Prevention of Malaria with Insecticide-Treated Nets

From Footsteps No. 33, “Insecticide-Treated Nets” & IAMAT (International Association for Medical Assistance to Travellers), “How to Protect Yourself Against Malaria” 2000 edition.

Over 2.5 million people, mostly in Africa, die from malaria every year. Malaria is caused by a parasite called Plasmodium carried by the female Anopheles mosquito. She bites people and animals in order to obtain blood which she needs to develop of her eggs.

The Anopheles mosquito can be recognized by its posture. It looks as if it is standing on its head with the rear legs up in the air. Other mosquitoes sit flatter on a surface. Anopheles are also silent; they do not buzz around your head but instead fly straight towards you.

Mosquito nets are effective in protecting people sleeping under them as long as the nets have no holes and people are not sleeping up against them. However, a mosquito will continue searching until it finds a way in or finds part of the body that is against the net where it can bite through.

Using insecticide-treated nets has shown to bring a 20-60% reduction in malaria. When a mosquito encounters a treated net they will either die or fly away.

Nets are first placed into a dilute liquid insecticide mixture. The nets should be clean and dry. You can use insecticides such as permethrin, deltamethrin or lambdacyhalothrin.

Calculate the area of the net you want to treat. Remember that some nets are shaped such that you must measure height as well as length and width. For rectangular nets, add up the total surface area (two times the area of the sides plus two times the area of the ends plus the area of the top). With a circular net, lay it out flat and then multiply the base circle area measurement by the height.

Next, measure how much liquid one net soaks up. Put a measured amount of water into a bowl, soak the net in it and then wring it out into an empty container. Measure the wrung out amount and subtract this from the original amount of water to find how much water the net soaks up.

To estimate the amount of insecticide needed (in ml), you multiply the recommended dosage (mg/m²) by the area of the net (m²) and divide that by the concentration of the insecticide (%) times ten.

For instance, deltamethrin is sold by the trade name KOthrin. It comes in a concentration of 2.5% (sometimes written as 25 ml/liter or 25 ppt) and the dosage is 25 mg/m². If your net is 6.5 m², you multiply 25 x 6.5 and divide that by 2.5 x 10, coming up with 6.5 ml.

Put that amount of insecticide into the amount of water you have estimated that your net can soak up. Use rubber gloves and work outside. Soak the net, wring it out and then dry it. They are then ready to be hung. Wash all your equipment, clothes and skin with soap and water and properly dispose of leftover insecticide and bottles. The nets only need to be treated twice a year.

For those who can’t afford nets, curtains can be treated in the same way, or other materials can be used in the place of mosquito netting.

Other ways to prevent bites:

Wear long-sleeved shirts and trousers after dusk. Light colored clothing seems to help as mosquitoes are more attracted to dark clothing. Avoid wearing perfume or aftershave. Use mosquito repellent on your skin and clothes.

Spray bedrooms with pyrethrin insecticides at night before going to bed. Mosquitoes like to hide in dark corners, in closets, under beds, etc.

Tie up mosquito nets during the day. Check for mosquitoes when putting them down at night. Mend holes and tears in the nets. Make sure the net is tucked in around the sleeping person, and as much as possible, avoid touching the net while sleeping.

Avoid leaving breeding places for mosquitoes such as uncovered containers of water. Garlic sprays will also keep the larvae away from standing water.