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[NAIROBI] A set of chemicals that confuse mosquitoes' navigation could boost the fight against diseases such as dengue and malaria, according to a study.

Mosquitoes sense wafts of carbon dioxide (CO2) exhaled by humans and use it to track down their target. Now, scientists in Kenya and the United States have found three classes of molecules that can interfere with mosquitoes' odour receptors and hamper their ability to find humans to bite.

CO2 is already being used in mosquito traps and traps containing human odours are also in development. But this new strategy would mask the presence of humans, say the researchers.

"The idea is to be able to disable large numbers of mosquitoes from finding human beings and mask a large area such as a backyard or an abode like a hut," said Anandasankar Ray, co-author of the paper, published in Nature this month (2 June), and an entomologist at the University of California, Riverside, United States.

The researchers knew that fruit flies, which have similar CO2 receptors to mosquitoes, are attracted to ripe fruits — even though such fruits emit CO2, which normally repels the flies. They found that ripe fruit also emits certain molecules that block fruit flies' CO2 detection, and identified several compounds that have the same effect on mosquitoes.

The team first tested the molecules in a wind tunnel, in which CO2 was released at one end and mosquitoes at the other. The mosquitoes exposed to inhibitory molecules before being released got lost along the way.

They then tested the odours in a large enclosure at the Nairobi-based International Centre for Insect Ecology and Physiology. Mosquitoes were released overnight into an enclosure of huts containing either attractive CO2 or a combination of CO2 and the newly discovered molecules. The following morning, the huts containing the molecules contained half as many mosquitoes as those in the unprotected huts.

"[The chemicals] are simple molecules that are inexpensive to purchase," said Ray. They come from natural sources, such as fruits and leaves, but could be synthesised in a laboratory if used for mosquito control, he added.

The resulting approach, Ray said, is effective even when it uses very low concentrations of the chemicals and small containers — offering an alternative to the expensive CO2 cylinders used in common traps.

Repellent technologies have been used in Africa for decades, but they have been kept out of reach of the poor because of high costs, said Elizabeth Juma, head of the department of malaria control in Kenya's ministry of public health.

She cautioned that as blood is critical to mosquitoes' survival, they may eventually find a way to overcome such repellents.

Ray said the traps will need further research — large-scale field trials and safety analyses — before they are ready for commercial production, but he has started working with a US-based company to produce the traps cheaply on a commercial basis.

References

Nature doi:10.1038/nature10081 (2011)

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