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Author: Vanessa Ngan, Staff Writer, 2008.
Insect repellents are agents that are used to protect the body from the bites of insects that can cause local or systemic effects. Whilst some bites cause only local skin irritation, some can cause serious illnesses and possibly death as the insects act as carriers or vectors of diseases. Mosquito bites are a common problem throughout the world and in some areas the mosquitoes are the vector of potentially serious diseases including malaria, West Nile virus, dengue fever, and chikungunya fever. Lyme disease is spread via the bite of infected ticks on the skin.
Insect repellents currently fall into two categories: chemical repellents and natural plant-derived repellents. The most well-known and well-used chemical repellent is DEET (N, N-diethyl-3-methylbenzamide, previously called N, N-diethyl-m-toluamide). Other chemical insect repellents include IR3535, MGK-326 and MGK-264. The latest chemical agent proving to be as effective as DEET is a piperidine-based repellent called picaridin. Plant-based insect repellents are becoming increasingly popular because of their low toxicity but to date have not shown to be as effective as DEET. These include citronella, soybean oil and eucalyptus products.
The ideal insect repellent should aim to have the following properties:
Currently there are no insect repellents that meet all the criteria listed above. It is extremely difficult to find a single active chemical that is effective against the many different species of disease-carrying insects. DEET is the most broad-spectrum and most effective insect repellent that has been developed to date. However it has recently been discovered that the chief malaria-carrying mosquito, Anopheles albimanus, in the United States is becoming resistant to DEET.
To understand how insect repellents work we need to understand how biting insects find their hosts. Studies of mosquitoes have shown that these insects use a combination of sight, heat and smell to locate a blood meal. They are attracted to the smell of carbon dioxide, lactic acid and other odours from the skin, as well as warm and moist skin.
Most insect repellents including DEET work on the principle of creating a vapour barrier that deters the insect from coming into contact with the skin. To the insect the vapour has an offensive smell and tastes bad.
Currently under investigation by scientists with the International Anopheles Genome Project is the olfactory biology of the main malaria-carrying mosquito Anopheles gambiae. To find a host to feed on, mosquitoes use their olfactory binding proteins (OBPs) to detect human-specific odours that are released by human skin. Scientists believe that by destroying the OBPs of mosquitoes this should stop them from targeting human hosts and effectively decrease bites.
The combination of permethrin-treated clothing and the application of a chemical-based skin repellent should effectively protect against most biting insects, even in areas with high populations of the insect-biting critters.
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