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Preventing mosquito-borne infections

FEATURED REVIEW Malaria is a major public health problem in 90 countries. Effective protection against mosquito bites is particularly important where there is a high risk of potentially severe infections. Prescrire conducted a review of the evidence to determine how to prevent mosquito bites both effectively and safely.
Full review (4p) in English available for download by subscribers.

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  • Our last review on arthropod repellents in 1994 concluded that DEET was the cutaneous repellent with the best risk-benefit balance. Other insect repellents, including icaridin and citriodiol, are now better evaluated. We have conducted a review of the evidence available in mid-2008, in order to determine how to prevent mosquito bites both effectively and safely.
  • Different repellents provide protection for varying lengths of time, mainly depending on the insect species, the environment, the user, and the concentration of repellent applied. DEET remains the best-assessed repellent. In a randomised placebo-controlled trial conducted in Pakistan, cutaneous application of DEET and permethrin reduced the frequency of malaria attacks.
  • Studies of repellent efficacy against the main vector mosquito species, in the laboratory or in the field, have shown that the effect of IR35/35 lasts as long or almost as long as that of DEET.
  • Icaridin is at least as effective as DEET against Anopheles gambiae, the principal vector of malaria in Africa, and Aedes aegypti, a vector of dengue fever. One field study showed that citriodiol was about as effective as DEET against Anopheles gambiae.

  • The adverse effects of DEET are well known, due to its extensive use. French and American poison control centres report that serious neurological adverse effects are rare. DEET causes skin and eye irritation and can cause urticaria. Icaridin is also an irritant, and adverse effects have about the same frequency as with DEET. According to French poison control centres, IR35/35 is better tolerated than DEET. In early 2008, no serious adverse effects had been reported with IR35/35, icaridin or citriodiol. Experience with citriodiol is limited.
  • Recommendations on repellent use by children and pregnant women differ from one country to another. DEET is often recommended from the age of 2 months, but at a moderate concentration of about 30%. A placebo-controlled trial of DEET in 897 women who were in their 2nd or 3rd trimester of pregnancy showed no effect on the outcome of pregnancy or on the unborn child. The United States, United Kingdom and Canadian health authorities recommend DEET for pregnant travellers. In France, only IR35/35 is recommended for pregnant women, with no explanation for this preference.
  • Many studies in Africa and Asia have shown that permethrin-treated nets offer more effective protection against insect bites than standard nets, and that they reduce the risk of malaria. They have few adverse effects, apart from skin, eye and nose irritation for a few days after the nets are treated with permethrin.
  • The protection provided by various devices that release insecticides in the home is poorly assessed and their possible long-term toxicity is not known. However, randomised trials have shown that spraying of homes with long-acting insecticides in endemic areas reduces the risk of malaria attacks.
  • In practice, combined use of ample clothing covering as much exposed skin as possible, cutaneous DEET (or perhaps icaridin), insecticide-treated nets, and chemoprophylaxis helps to prevent malaria and, by extrapolation, the other more or less serious infections carried by mosquitoes.

    ©Prescrire January 2009

    Source: Prescrire International 2008; 17 (98): 250-253.

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