The Aedes aegypti, the mosquito known as dengue or yellow fever, is one of the most dangerous for humans as it is a carrier of these and many other diseases. These mosquitoes have a relentless system when it comes to detecting their prey. Now we are beginning to find out how they do it.
A guided peck.
We know that smell is key for mosquitoes, when it comes to locating and choosing their victims (although it is not the only resource they have). The carbon dioxide that we exude when we breathe is one of the chemicals that these animals detect, as well as some chemicals that result from our sweat, such as octenol or some aldehydes.
The Aedes aegypti it is also a specialized attacker: it only feeds on blood when it is human (bearing in mind that only female mosquitoes bite when they need protein for their eggs) and avoids biting other animals, not even other mammals. A new study looks at how this “unbreakable attraction” to humans can overcome even the hurdles we try to put as many hurdles on them as possible.
Despite not having a central nervous system, the neurons of these mosquitoes have broken the schemes of scientists. And it was because of the receptors dedicated to smell that the neurons of these animals have.
A study recently published in the journal Cell has shown that the smell of mosquitoes is very different from what was believed. In their study, the team found that each of the neurons in the mosquito’s olfactory system can detect a variety of chemical compounds.
Qualify an investigation that was worth a Nobel.
The scientific consensus had been established by a group of researchers who, investigating in mice, discovered that the olfactory system was highly specialized. Each olfactory neuron expresses a specialized receptor for a specific type of odor, which communicates with a group of nerve endings called the glomerulus.
This specialization, which does not occur for example in the sense of taste, would make evolutionary sense. According to Margaret Herre, the first author of the article, this “would give animals the ability to live in a rich olfactory space, detecting and distinguishing a huge range of odors.”
Leslie Vosshall worked in the laboratory of Richard Axel, one of the scientists who won the Nobel Prize in 2004 thanks to this research. She is now one of the researchers who has put a huge “but” in her research by discovering the ability of mosquito neurons to detect a variety of odors.
For the team, nuanced this consensus was surprising. Each cell seemed to express everything in a supposedly hyper-specialized system, Vosshall explained. Nothing seemed to make sense at first glance.
Having this redundancy in the neurons gives mosquitoes a great advantage over the tricks that humans have created to escape from their bites. It makes it harder for us to sneak around by blocking just one group of chemicals.
“The way in which the moquito organizes its sense of smell is totally unexpected,” says Vosshall in one of the published press releases. “But for the mosquito it makes perfect sense. Every neuron that interprets odors is so redundant that the olfactory system is essentially unbreakable. This may explain why we haven’t found a way to overcome the attraction of mosquitoes to humans.”
The discovery came as the team was analyzing the response of mosquito neurons to carbon dioxide. Using the CRISPR gene-editing tool, they added a fluorescent protein to neurons with CO2 receptors and another to neurons responsible for responding to chemicals in our Body odour. They thus discovered that the same neurons could be activated by different odours. It just couldn’t happen.
The results of the first analysis surprised the team so much that they used different methodologies to confirm it. One of these methodologies was single core RNA sequencing (snRNA-seq), which confirmed the results. A new system for using electrodes to analyze the olfactory system of mosquitoes also helped confirm the results.
The fruit fly, another exception.
But perhaps the experiment with the greatest confirmatory value came from another team and another animal: the fruit fly. Christopher Potter of Johns Hopkins University found that the fruit fly (an animal that coincidentally had also been studied by Vosshall years before) had a similar olfactory system.
Better repellents and techniques to avoid their bite.
This finding doesn’t tell us how to combat bites from this dangerous insect, but it does at least tell us what we’ve been doing wrong. Camouflaging a specific smell is of little use when the animal is easily able to detect us using another. Perhaps the answer therefore lies in other tactics, such as overloading the mosquitoes’ olfactory system or using traps to deflect them. Or even more radical ones.
Road still to go.
The team has admitted that all