Mosquitoes and human diseases: understanding how we smell could save lives

Featured Sponsor

Store	Link	Sample Product
UK Artful Impressions	Premiere Etsy Store

CNN
—

Of the more than 3,000 species of mosquitoes in the world, only a small number have evolved to specialize in sucking human blood.

It’s not currently known how mosquitoes that bite humans track us so effectively, but it’s important because they don’t just make us bite. They also carry dangerous diseases like Zika, dengue, West Nile virus, and malaria that can be deadly.

In fact, stopping these pesky insects in their tracks could save up to half a million lives lost to these diseases each year.

“In every one of those cases where a mosquito has evolved to bite humans, which has only happened two or three times, they become vectors of nasty diseases,” said Carolyn “Lindy” McBride, an assistant professor of ecology. and evolutionary biology at Princeton Neuroscience. Institute in New Jersey.

That’s why he wants to understand how they find and target humans.

“Mosquitoes mostly choose what to bite based on odor,” said McBride, whose lab focuses on the Aedes aegypti species of mosquito that evolved to bite humans specifically.

Only female mosquitoes suck blood as they need it to produce their eggs. Knowing how a potentially disease-carrying female mosquito sniffs out a person, while she ignores other warm-blooded animals, is a key question.

Once better is known, much more effective repellents, or baits, could be made to keep mosquitoes away from humans and save lives, said Christopher Potter, an associate professor of neuroscience at Johns Hopkins University’s Center for Sensory Biology.

If scientists can control their sense of smell, “we can really control what these mosquitoes do,” said Potter, who is studying another human-specific mosquito, Anopheles, that transmits malaria.

This is not an easy question to answer, since any animal odor is made up of hundreds of chemical compounds mixed in specific proportions.

“The actual chemicals found in human odor are basically the same as those found in animal odor — it’s the proportions and relative abundance of those compounds in human mixtures that is unique,” McBride said. , whose investigation focuses on those issues.

Every time a hungry female mosquito flies by, it’s doing complex chemical math in its little brain, figuring out what’s a human, what’s a dog, and what’s a flower.

“To investigate, we decided to record neural activity in the brains of women while exposing them to extracts of natural human and animal odors,” Zhilei Zhao, a graduate student in McBride’s lab, wrote in a Twitter thread describing lab work. It took four years to develop “the necessary genetic reagents, scent delivery systems, and analytical approaches,” Zhao wrote.

McBride’s lab team created a library of the chemical composition of animal odors. “That data set doesn’t actually exist, so we decided to go out and collect it ourselves,” said Jessica Zung, a graduate student in McBride’s lab.

Zung has collected scent samples from around 40 different animals so far, including guinea pigs, rats, quail and more.

When comparing some of them with the 16 human samples, something jumped out. Decanal, a simple and common compound, is particularly abundant on human skin, Zung said.

Ubiquitous in the natural world, in humans, decanal comes from another, more complex compound. Zung searched the archives to find 1970s research (a lot of this was originally done to find a cure for acne) detailing how when a component of our skin’s natural oils, sapienic acid, breaks down, it’s left decanalized. This acid (as the name implies) is only found in humans. It’s what probably leads to the high levels of decanal that help mosquitoes smell their way to us, but more study is needed.

Understanding what mosquitoes sniff out is only part of the story; knowing how they do it is also important. To see exactly how mosquitoes use this sense, the scientists bred genetically modified Aedes aegypti mosquitoes “so we could open up their tiny heads and put them under a fancy microscope and really see how neurons fire when exposed to human and animal odors. McBride said.

The research team already knew that mosquitoes have about 60 different types of neurons that detect odors, so when they looked at the insects’ brains, they thought they might see a lot of activity. But it was surprisingly quiet, which means the signal was perhaps quite simple, with just a couple types of neurons.

“One type of neuron responded very strongly to both humans and animals. Another type of neuron responded to both, but responded much more strongly to humans than to animals,” McBride said of that job. So it can be as simple as that mosquito’s brain comparing just two types of neurons.

This type of research has only been possible since the technology to study mosquito brains in detail became available, which was only recently. “It’s traditionally been very difficult to study this at the level we’re doing now,” Potter said.

Incredibly, mosquitoes that attack humans have evolved to be able to do this in the last 5,000 years, making it a “really amazing example of rapid evolution,” McBride said.

The Aedes aegypti, also known as the “yellow fever mosquito,” also transmits dengue, Zika, and chikungunya. The creature originated in Africa and likely reached its current range in the southern United States and Central and South America on slave ships during the 17th century, according to McBride.

These diseases combined kill and sicken thousands of people a year, which is why mosquitoes have been called “the world’s deadliest animal” by the US Centers for Disease Control and Prevention.. McBride and Potter hope their work can be used by others working on repellents and attractants to prevent disease.

As for insider knowledge on how to avoid getting bitten in your own backyard, McBride said he uses a fan.

“Have it blow air over where you’re sitting outside or over the grill or under the table where your feet bite.” It’s not like you’re blowing the scent to deflect mosquitoes, she said.

It’s simply because these deadly creatures, McBride said, “are not great fliers.”