Malaria: Prevention, external agents

Anopheles mosquitoes only bite in the evening and at night. It is possible to protect oneself by wearing protective clothing and using an undamaged mosquito net. Effectiveness is increased by treating the net with pyrethroids (insecticides) such as permethrin (Permas®, Peripel®), lambda-cyhalothrin (Iconet™) or deltamethrin (K-Otrine®). This will increase further in importance in the future. The substances are derived from pyrethrum, a product originating from Tanacetum cinerariifolium (= Chrysanthemum cinerariifolium) and C. coccineum, herbaceous composite-flowered plants (fam. Compositae) which are similar to large daisies. In emergencies where mosquito nets are logistically difficult (e.g. camps after heavy floods), impregnated blankets can be used. These will probably be less effective than impregnated bednets.

Fine-mesh gauze can be applied to windows and ventilation shafts. One good argument for using a mosquito net is the fact that it also protects from nuisance insects such as Culex mosquitoes and bedbugs. In regions where there are few Culex, people are not so ready to use a net: after all they cannot see or hear any mosquitoes. (Anopheline mosquitoes fly noiselessly.)

Insecticides based on pyrethrum can be dispersed by means of spraying (spray gun), evoparation (heated electric plate) or burning (mosquito coil, e.g. with esbiotrin). Insecticides can also be applied to the walls or to the curtains by the windows. There are also various insect repellents. DEET (N,N-diethyl-m-toluamide, now called N,N-diethyl-3-methylbenzamide) is moderately active and can be applied as an alcoholic solution to the skin. This produces a sticky effect when the alcohol evaporates, however. The effectiveness is only moderate. DEET is absorbed through the skin and is eliminated quickly via the urine. There is no accumulation in the body. Other repellants include KBR 3023 (Autan active®) which has the same effectiveness as DEET, but is non-irritant and does not affect plastic (spectacles), dimethyl phtalate (low activity) and ethohexanediol. Essential oils such as citronella, cedar, eucalyptus, neem (obtained from the tree Azadirachta indica) and geranium are short-acting and not very effective. People who need to stay in regions which are heavily infested with mosquitoes, can apply permethrin to their clothing. Taking extra vitamin B and electronic buzzers are of no use.

The product containing IR3535 (ethyl butylacetylaminopropionate) has been subjected to well- controlled field studies. The results demonstrate a protection time for the product of up to three hours or more against mosquitoes. Case studies are not a valid substitute for repellent field studies. Only field studies are to be used to establish efficacy of insect repellants.

Category: Medicine Notes