Malaria - Prevention using Mosquito Nets

Types of mosquito nets

Fabric

Polyester netting (a man-made fiber) is the most common fabric for nets; it is light and does not absorb much water. Cotton cloth or netting soak up a lot of water and therefore require chemical treatment. Polyethylene (monofilament) is a very strong man-made fiber that absorbs very little water.

Denier

Denier is the strength of the fiber used to make the mosquito net. The strongest is 100; anything below 70 is usually too weak and tears easily.

Mesh size

Mesh size is measured in either millimeters (mm) or in holes per square inch. Ideal mesh sizes are 1.5 to 2 mm or 196 (14 x 14) holes per square inch. Some nets have larger holes which allow for better ventilation but will only offer protection as long as they remain treated.

Shape

The two most common shapes are conical) and square. There is less person to net contact under a square net but many people prefer the easy-to-hang conical net. Wedge-shaped, triangular, and tent-like nets can also be made.

Colour

Mosquito nets can be any colour, however white is most frequently found in those made from netting. Now that people are using insecticide and washing their nets less frequently, darker-coloured nets are becoming more popular.

Size

Some mosquito nets indicate the size of bed that they will cover in meters or feet. Others state small, medium, and large, or single or double. If possible, look at the net before you buy it. If you are buying in bulk, try to get samples to test where they will actually be used.

 

How to treat mosquito nets with insecticides

Always use metric measurements: centimeter (cm), meter (m), millimeter (mm) milliliter (ml) and liter (l). All nets should be clean and dry.

1. Calculate the area of the net, in square meters. Consider a conical net as a triangle and a square net as a rectangle.

   How to measure a mosquito net
   Conical net
   Lay the net flat.

   1. Measure the curved base (m).
   2. Measure the height (m).
   3. Multiply base x height = area of net.

   Rectangular net
   Hang the net up.

   1. Measure the area at the top = width x length.
   2. Measure the area around the sides = height x total distance around base of net.
   3. Add the two measurements together to find the total area of the net.
2. Calculate the amount of water absorbed by the net, in ml or liters. Using a bucket and a measuring container, measure two liters of water into the bucket. Soak the net until it is totally wet. Carefully wring out the net over the bucket. When the net has stopped dripping, measure the water remaining in the bucket.

   For example:
   2 L - 1.3 L = 0.7 L (700ml)
   original water in bucket - remaining water in bucket = water absorbed by the net

3. Calculate the amount of insecticide required.
   • Check the recommended dosage of insecticide. Read the instructions on the bottle or check the table below.
   • Check the concentration of the insecticide. This follows the name of the insecticide. For example, permethrin
   • EC 50, contains 500g of insecticide in each liter; this is also known as a 50% solution.

   Dosages of commonly used insecticides
   (in mg of insecticides per square metre of material ~ polyester)
   Compound and formulation Dose (mg/sq metre)
   Permethrin EC 200 - 500
   Deltamethrin SC 15 - 25
   Lambda-cyhalothrin CS 20
   Cyfluthrin (oil in water emulsion) EW 30 - 50
   Etofenprox EC 200
   Alpha-cypermethrin WP 20
   (Curtis 1996 WHO)

   To calculate the amount of insecticide use the following formula: Dosage(mg) x Area of Net
   divided by
   Concentration of Insecticide % x 10

   For example:
   If you want a dosage of 200mg/m2 on a 11m2 net and you are using Permethrin 50 (a 50% concentration contains
   500g insecticide per litre) you would calculate the amount required as follows:
   200 x 11 = 4.4 ml insecticide
   divided by
   50 x 10

   If you have found that this specific net absorbs 0.7 litre (700ml) of water, add this amount of water to the insecticide to make a final mixture.

   If more than one net is being treated (using the above example) multiply the amounts as follows:
   No. of Nets Insecticide (ml) Water (litres)
   1 4.4 0.7
   10 44 7
   20 88 14

4. Measure the amount of water and insecticide needed. Wide-mouth containers, such as an empty cooking fat container (1 kilo = approximately 1 litre), are best for measuring large amounts of water.

   Insecticide can be measured using a 250g empty container which can be scored inside at 50ml intervals. For small amounts of insecticide a syringe could be used. The insecticide may dissolve the markings on the syringe so it is useful to score the outside with a knife.

5. Protective gloves must be worn.
6. Add the insecticide to the water and mix well. Treatment should be performed out-of-doors or in a well-ventilated area. If you are treating a few individual nets you can place each net in a carrier bag add the insecticide and water solution, knead well and let the owners carry their net home in the bag.
7. Dip the net in the solution until it is thoroughly wet.
8. Wring the net out over a bowl and hang it up until it has stopped dripping.
9. Dry the net. They can be laid on beds and bedding (which will help to kill bedbugs) or dried outdoors. Do not place them in direct sunlight for more than a few hours.
10. Wash your hands and all equipment with soap and water.
11. Pour any waste insecticide down a pit latrine and NOT into a river or pond.

 

For more information, contact us:

The Director
ICA
P.O.Box 26012
Ottawa, Ontario
Canada K2H 9R6

email:  admin@igbocharitable.com