June 2, 2011

Chemicals ‘Fool’ Mosquitoes In Malaria Breakthrough

In a dramatic breakthrough in the battle against malaria, researchers have identified a low-cost chemical that interferes with a mosquito's ability to detect humans, scientists said on Wednesday.

Experts hope the findings could help develop the next generation of mosquito traps and repellents, which could confuse, deter or trap the insects.

The chemicals consist of odor molecules that disrupt carbon-dioxide sensors that alert mosquitoes to exhaled human breath, which signals the presence of a nearby human, the researchers reported in the journal Nature.

The discovery could prove invaluable to poor tropical countries, providing an alternative to DEET, a costly skin repellent that requires repeat applications and is showing alarming signs of resistance.

"These chemicals offer powerful advantages as potential tools for reducing mosquito-human contact and can lead to the development of new generations of insect repellents and lures," said study leader Anandasankar Ray, an assistant professor of entomology at the University of California at Riverside.

Although mosquito traps in the form of dry ice, gas cylinders of carbon dioxide or propane combustion exist today, they are are too bulky and costly to be used for widespread mosquito control, particularly in poor nations.

However, future mosquito traps could be "highly portable, convenient and easily replenishable," Ray told the AFP news agency.

Malaria took the lives of some 781,000 lives in 2009, according to data from the United Nations' World Health Organization.  Some 90 percent of malaria deaths each year occur in Africa, 92 percent of which are children under the age of five.

Other mosquito-borne diseases include dengue, yellow fever, filariasis and West Nile virus.

Ray and his team expanded on previous research with fruitflies, and examined three mosquito species whose females are disease vectors: Anopheles gambiae, Aedes aegypti and Culex quinquefasciatus.

The odor molecules they identified disrupt receptor cells for carbon dioxide located in small, antennae-like appendages close to the mosquito's mouth.  These receptors are activated by the smell of carbon dioxide, triggering a signal in the brain that prods the mosquito into fly upwind, following the smell of CO2 until they reach its source.

The three classes of the odor molecules the researchers identified are:

"¢ Inhibitors: Odor molecules, like hexanol and butanal, that inhibit the carbon dioxide receptor in mosquitoes and flies.'

"¢ Imitators: Odor molecules, like 2-butanone, that mimic carbon dioxide and could be used as lures for traps to attract mosquitoes away from humans.

"¢ Blinders: Odors molecules, like 2,3-butanedione, that cause ultra-prolonged activation of the carbon dioxide sensing neurons, effectively "blinding" the mosquitoes and disabling their carbon dioxide detection machinery for several minutes.

"These chemicals offer powerful advantages as potential tools for reducing mosquito-human contact, and can lead to the development of new generations of insect repellents and lures," said Ray.

"The identification of such odor molecules "“ which can work even at low concentrations, and are therefore economical "“ could be enormously effective in compromising the ability of mosquitoes to seek humans, thus helping control the spread of mosquito-borne diseases."

Mosquitoes can also use heat sensors and sight to identify their next meal.

The study was published June 2, 2011, in the journal Nature.


Image 1: Aedes aegypti mosquito. Credit: James Gathany, PHIL, CDC

Image 2: This image depicts scanning electron micrographs of the heads of a Culex quinquefasciatus mosquito (foreground) and Drosophila melanogaster (fruit fly; background). Representative traces of a CO2-sensitive neuron activated by CO2 (top trace) and inhibited by addition of odor 2,3-butanedione (bottom trace). The structures of CO2 and 2,3-butanedione are also shown. Credit: S. Turner, UC Riverside


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