From malaria to Zika, the West Nile virus to yellow fever, mosquitoes transmit some of the most potent and potentially dangerous diseases on the planet, but research published earlier this month in the journal Nature Communications has identified a novel way to combat some of them.
In the study, Dr. Christopher Potter, an assistant professor of neuroscience at the Johns Hopkins University School of Medicine, and his colleagues reported on the identification of a specialized region of the insect’s brain that combines smells and tastes to create its favorite flavors.
Using this knowledge, they propose the possibility that a substance could be used to make the “flavor” of humans repulsive to malaria-bearing mosquito species. By making us taste bad, the researchers explained, they could discourage the insects from biting people, thus preventing the spread of a disease that kills a reported 450,000 men and women annually.
“All mosquitoes, including the one that transmits malaria, use their sense of smell to find a host for a blood meal,” Dr. Potter said Monday in a statement. “Our goal is to let the mosquitoes tell us what smells they find repulsive and use those to keep them from biting us.”
A mosquito with modified olfactory neurons (Olena Riabinina and Courtney Akitake, Johns Hopkins Medicine)
New technique identifies the neurons that process smell, taste
Smell is essential to mosquito survival, the study authors explained. For this reason, each of the insects uses three distinct sets of organs to detect odors: two antennae, two maxillary palps (thick appendages protruding from the bottom of their heads) and two labella (regions that contain both olfactory and taste-sending neurons and are located at the tip of the proboscis).
Dr. Potter and his team focused their studies on the female Anopheles gambiae mosquito, which is the species of insect responsible for spreading malaria by transmitting infectious parasites, by learning more about how the creature receives and processes olfactory data through each of these different sensory regions, and which regions of the brain this information travels to.
Using a powerful genetic technique that the researchers claim had never been used successfully in mosquitoes before, they made it so that the neurons which received complex odors through a type of protein known as an odorant receptor (OR) would glow green. These OR neurons, they explained, have been shown to distinguish humans from other types of warm-blooded mammals in the Zika-carrying Aedes aegypti mosquitoes, Dr. Potter’s group explained.
“This is the first time researchers managed to specifically target sensory neurons in mosquitoes. Previously, we had to use flies as a proxy for all insects, but now we can directly study the sense of smell in the insects that spread malaria,” explained lead author Dr. Olena Riabinina, currently a postdoctoral fellow at Imperial College London. “We were pleasantly surprised by how well our genetic technique worked and how easy it is now to see the smell-detecting neurons.”
Discovery could lead to development of new type of insect repellant
The researchers discovered that OR neurons from the antennae and maxillary palps traveled to the antennal lobes, a symmetrical part of the brain which serves a similar function in flies. Much to their surprise, however, they found that OR neurons from the labella were sent to a part of the brain previously unassociated with smell known as the subesophageal zone.
Since the subesophageal zone had previously been linked to the sense of taste, Dr. Potter said that the new discovery “suggests that perhaps mosquitoes don’t just like our smell, but also our flavor. It’s likely that the odorants coming off our skin are picked up by the labella and influence the preferred taste of our skin, especially when the mosquito is looking for a place to bite.”
This discovery could provide scientists with a new way to repel these disease-causing insects. Since mosquitoes use their labella to directly probe a person’s skin before biting them, the new research suggests that some substance could be used to target the labellar neurons, causing the insects to be disgusted by the smell or test of our skin before actually breaking the skin.
Dr. Potter believes that such a repellant could be combined with another substance that keeps mosquitoes at bay by targeting the antennal neurons, and that the genetic system his team came up with could make it easier to find odorants that are “safe and pleasant-smelling” for humans, but which are “strongly repellant to mosquitoes at very low concentrations.”
They also plan to further analyze the neurons of these mosquitoes to learn how signals from all three of the insects’ olfactory receptors interact to influence their behavior. “We’d like to figure out what regions and neurons in the brain lead to this combined effect,” Dr. Potter noted. “If we can identify them, perhaps we could also stop them from working.”
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Image credit: Thinkstock
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