Researchers discover how mosquitoes know where you are

Disabling a specific protein makes them lose interest in using humans as food sources. Samantha Page reports.

Mosquitoes use a combination of odour, carbon dioxide and heat to detect their victims.

Bernard Lynch/Getty Images

Researchers are a step closer to preventing the dreaded mosquito bite, after potentially pinpointing how the insects smell humans.

The Aedes aegypti mosquito relies on a cell-surface protein called an ionotropic receptor (Ir8a) to detect the smell of humans and human sweat. When it is disrupted, the insects lose this ability, neurobiologists report in the journal Current Biology.

“Removing the function of Ir8a removes approximately 50% of host-seeking activity," says senior author Matthew DeGennaro of Florida International University in Miami, US.

“Odours that mask the Ir8a pathway could be found that could enhance the efficacy of current repellents … In this way, our discovery may help make people disappear as potential hosts for mosquitoes.”

Of course, this news isn’t just good for those who suffering from mosquitoes’ signature itchy, red welts. A. aegypti can carry a slew of nasty and sometimes fatal illnesses.

“The transmission of diseases like dengue, yellow fever, Zika, and malaria can be blocked if we stop these mosquitoes from biting us," DeGennaro says. “In order to find new solutions to prevent mosquito bites, we need to focus on understanding the molecular basis of mosquito behaviour.”

The researchers posit that lactic and carboxylic acids, which occur in human sweat, might be how the insects distinguish humans from other vertebrate hosts.

To conduct their study, DeGennaro and colleagues used the CRISPR/Cas9 gene-editing system on A. aegypti specimens, disrupting Ir8a. The resulting mosquitoes were less attracted to humans or human scent. They also had no interest in lactic acid.

In previous research, the same team had established that disrupting primary olfactory receptors did not stop the insects seeking a human-sourced feed.

“This suggests the olfactory receptors that remain, such as the ionotropic receptors, could play a significant role in host detection,” they note.

Mosquitos are sensitive to smell, carbon dioxide and heat, all of which have an influence on their host-seeking behaviour.

"The Ir8a phenotype was not modulated by carbon dioxide, but required the function of the carbon dioxide receptor," DeGennaro explains.

“This suggests that carbon dioxide is necessary to activate the Ir8a response to acidic volatiles in human odour, but not sufficient to rescue the mutant phenotype. Our results strongly suggest that host odour detection by Ir8a is an indispensable component of the mosquito's host detection system."

Next step: Figuring out how to cripple Ir8a without needing to genetically alter every mosquito on the planet.

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