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Last Updated: Thursday, 15 January, 2004, 08:39 GMT
Chemical key to mosquito biting
By Helen Briggs
BBC News Online science staff

Mosquito, BBC
Another possible route to attack the insect
A key chemical found in sweat is what draws the mosquito that spreads malaria in Africa to bite its human victims.

US researchers at Yale and Vanderbilt believe knowledge of the molecule and the way it works could lead to a range of new anti-mosquito sprays and traps.

Malaria is caused by a microscopic parasite carried in the mosquito and is passed from one human to another every time the pest takes a blood meal.

John Carlson's team at Yale reports its work in the scientific journal Nature.

Insect reaction

Only the female mosquito bites people, tracking down a human victim largely using its keen sense of smell.

It can do this over considerable distances - a mosquito may pick up its target from hundreds of metres away.

But precisely how the deadly insect does this has always been a mystery - until now.

Carlson's group has identified the precise chemical pathway. Genetic engineering experiments on insects have shown that a whiff of human sweat is enough to trigger nerve cells in the mosquito's antenna.

The chemical, or odorant, in sweat responsible for this attraction is called 4-methylphenol. The Yale and Vanderbilt scientists have even found the receptor on cells that picks up molecule. It is called AgOr1.

A second receptor, AgOr2, appears to respond to a different sweat constituent, 2-methylphenol.

Big killer

John Carlson of Yale University's department of molecular, cellular and developmental biology, told BBC News Online: "It's the first time that a particular chemical receptor from a mosquito has been shown to respond to a human sweat odorant.

"It is only found in the female mosquito, which is interesting because it's only the female that bites people."

The work raises hopes for a breakthrough in fighting malaria. This is a complex area of research, however.

Previous studies have shown that human sweat contains about 350 different aromatic compounds and determining which ones play significant roles will be a great undertaking.

Nevertheless, the researchers think their work could be used to make more effective trapping systems for mosquitoes - and new repellents, too.

"Looking at attractants is only half of the picture. There is no evidence that mosquitoes find some human odorants repellent, but we're interested in exploring this," said Nature co-author Laurence Zwiebel.

More effective repellents could play a major role in reducing the death toll from diseases spread by mosquitoes, including malaria, encephalitis, West Nile, dengue, hemorrhagic and yellow fevers.

In Africa, the Anopheles gambiae mosquito is the principle carrier of the malarial parasite Plasmodium falciparum, the most dangerous of four different parasites.

There are at least 300 million acute cases of malaria each year globally, resulting in more than a million deaths. Around 90% of these deaths occur in Africa, mostly in young children.

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