Project nose

A mission to prevent mosquitoes from smelling out humans

By Tiasa Adhya
Published: Monday 15 March 2010

imageWhen  it comes to the Anopheles  mosquito, the beleaguered infectious disease specialists will try any idea to achieve a breakthrough. From developing more powerful insecticides that the pests seem to shrug off to targeting their newborns, scientists have tried almost everything. Yet, the 2009 World Malaria Report of who put half of the world’s population at risk of malaria. In 2008, an estimated 243 million persons were affected and nearly 863,000 died.
Biologists at the Yale University from usa decided to attack the bloodsuckers’ sense of smell. These scientists were investigating odour responses in fruit flies (Drosophila sp) when they hit upon the idea of subjecting mosquitoes to something similar. Humans emit several volatile scents in their sweat and breath. The compounds are detected by receptors located on the olfactory lobes of the mosquito’s antennae. But the specific compound that tells if it is a human was unknown.

“We dealt with the sensitivity of the olfactory system and its ability to distinguish odours,” said John Carlson, lead author of the study published in Nature on February 3. The group identified 27 odour receptors.

“We are working with the Anopheles gambiae odorant receptors, which we call AgOrs,” said lead researcher, Allison Carey, a PhD candidate in Carlson’s lab. The researchers isolated over 70 AgOr genes from the mosquitoes and expressed them, one at a time, in a Drosophila olfactory neuron that was mutated. Simply speaking what they did was fix the mosquito’s nose onto that of the fruit fly while blocking out its sense of smell. The group then presented a series of scent molecules (odorants), one at a time, to each receptor in the fruit fly and recorded 27,000 electrical responses. The receptors were found to respond positively towards a volatile compound called 4-methyl phenol—the natural odorant that is present in human sweat.

“Volatile compounds that activate the AgOrs may be useful in luring the mosquitoes into traps, or, if the compound very strongly activates the receptors, they may overwhelm and confuse the mosquitoes. On the other hand, compounds that block the AgOrs may be useful as repellents. Behavioural experiments are needed to test this,” concluded Carey.

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