Deadly and smart

London, Aug. 31: Scientists have worked out why mosquitoes make a beeline for certain people but appear to leave others almost untouched.

Specific cells in one of the three organs that make up the mosquito’s nose are tuned to identify the different chemicals that make up human body odour.

To the mosquito some people’s sweat simply smells better than others because of the proportions of the carbon dioxide, octenol and other compounds that make up body odour. It is those people who are most likely to be bitten.

The researchers believe the discovery of the way the mosquito smells will lead to the development of a new generation of repellents that would block mosquitoes’ nose — preventing them finding humans prey — within five to 10 years. While helping those people who always seem to get bitten and people with allergic reactions to bites, such substances could also save millions of lives in the fight against malaria, most prevalent life-threatening disease in the world. Mosquitoes use three organs to smell and taste — a feathery antenna which can identify a wide range of different chemicals, a proboscis used for short-range detection and the maxillary palp for longer range smelling. US scientists, whose research was published today in the journal Current Biology, have produced a detailed map of the maxillary palp.

They found it contains a series of highly specialised receptor cells used to detect the different components of human body odour.

Laurence J. Zwiebel, professor of biological sciences at Vanderbilt University in Nashville, Tennessee said: “What makes mosquitoes such good transmitters of malaria is that they are extremely good at finding people to bite. The amazing thing that we found was that all the sensory hairs that line the bottom of the maxillary palp are identical.”

“They are all attached to three neurons — one which is tuned to detect carbon dioxide, one which is tuned to detect octenol, and one which serves to enhance general olfactory reception. “We are looking to make a new generation of repellents based on targeting these molecular components in the mosquitoe nose.

“If you can block or hyper-stimulate these receptors, the mosquito would not do nearly as well at finding human prey.” Zwiebel added he expected the new repellents to be available for use within five to ten years.

The tips of the organs that make up the mosquito nose are perforated with thousands of tiny holes that let aromatic compounds to penetrate.

Once inside chemicals encounter the receptors that detect specific molecules that identify potential targets as human. Co-author of the research Tan Lu, also at Vanderbilt University, said: “These receptors are highly sensitive, which suggests that the maxillary palps serve as the malaria mosquito’s long-range detection system.”