How Do Mosquitoes Find Humans To Bite?

How Do Mosquitoes Find Humans To Bite?

Researchers Have Studied The Brains Of Mosquitoes To Find Out How They Can Find Humans Among Other Potential Prey.

It is midnight, and you hide in bed in a completely dark room up to your chin under the blanket. Suddenly, you hear the buzzing sound rushing past your ear.

A: Mosquitoes can use their sense of smell to find humans, even if that person’s scent is mixed with the scent of nearby animals and their surroundings. Some species of mosquitoes specialize in biting humans, and these little bloodsuckers are good at finding us. The question is, how do mosquitoes find their prey so carefully?

Humans emit certain odors that are distinct from those of other creatures, and for mosquitoes, this odor acts as a beacon that draws them to their next blood meal. “In total, there are more than 3,000 different species of mosquitoes, but only a handful of mosquitoes specialize in biting humans,” said Jilli Zhao, a neuroscience and behavior researcher at Cornell University.

Zhao and his colleagues studied one such species of mosquito called Aedes aegypti. This mosquito prefers feeding on humans to feeding on other animals. “AIDS Egypt loves humans,” said Matthew Dignaro, a neuroscientist and associate professor at the International University of Florida who did not participate in the study.

“They like our smell.”

Unfortunately, these pests carry many pathogens and can transmit diseases such as Zika, dengue fever, chikungunya, and yellow fever to humans. “We have known for a long time that AIDS is more attracted to humans than it is to other animals,” said Laura B. Duvall, an assistant professor in the Department of Life Sciences at Columbia University who did not participate in the study. “Because of this, they are a threat to public health.”

According to a 2022 report in the journal Nature Communications, previous studies have shown that AIDS Egyptian mosquitoes can sense the carbon dioxide we exhale and use this chemical signal to find and bite human flesh.

Dignaro and colleagues recently discovered that these pests could also smell some components of human sweat, including lactic acid. Another study showed that these mosquitoes are attracted to the bacterium Brevibacterium linens, which is a bacterium found on human feet and causes a specific Limburger cheese odor.

But although scientists know that all of these chemical symptoms help AIDS in Egypt target humans, most of these symptoms are present in humans and animals.

However, mosquitoes can somehow find humans, among other potential prey. Animals, on the other hand, emit similar odor compounds. “We did not know how they recognized the difference,” Duvall said.

Aedes aegypti mosquito

Egyptian Eid mosquitoes are sucking blood.

Zhao’s 2020 study, published May 4 in the journal Nature, focuses on the brain of tiny mosquitoes and offers a possible solution to the riddle.

The researchers first used the Crisper gene-editing technique to insert the genes encoding a fluorescent protein into mosquito DNA. They used female AIDS because the males drank nectar instead of biting humans.

When the gene was inserted, it directed the mosquito cells to attach the fluorescent protein to specific nerve cells in insects. By activating these neurons, the protein glows. “So, with the activation of the neurons, the fluorescence increases,” said Zhao, who was a doctoral student at Princeton University at the time of the study.

Thus, the researchers filled the odor processing center in the mosquito brain with luminous proteins and attached the proteins to mosquito odor detection organs such as the tentacles and lower jaw pulp (small sensory organs that exit the insect’s mouth).

They then exposed the mosquitoes to samples of odors they had collected from various animals, including rats, guinea pigs, quails, sheep, dogs, and humans. Each of these scents contained a mixture of different compounds released by animals.

Researchers cut tiny insect heads to see which areas of the mosquito’s brain are activated in response to different odors.

Their brains are tiny and only about half a millimeter wide. Using a microscope, the researchers removed the outer cuticle covering the mosquitoes’ heads and exposed their fluorescent brains. Mosquitoes survived this sensitive procedure. “Your hands have to be steady. Otherwise, you will destroy the brain,” Zhao said.

The researchers found that many onion-shaped nerves called glomeruli reacted strongly to human odors, but their response to animal odors was weak. They called these nerves human-sensitive glomeruli (H). A different glomerulus (A) showed the opposite pattern and reacted strongly to animal odors, but the third glomerulus (B) reacted strongly to all experimental odors.

To better understand these activity patterns, the researchers broke down animal odors into their constituent compounds to analyze them individually and in different combinations. They identified two compounds called “decanal” and “sub canal” that appeared continuously in high amounts in human fragrance samples but in small quantities in animal samples. These compounds have a sweet, citrusy odor similar to orange peel and are found in human sebum (an oil produced by glands in the skin).

Glomerulus H seemed to be specifically engineered to react with these compounds and responded strongly to the synthetic combination of the two. Glomerular B, meanwhile, reacted mildly to the odor, and glomerulus A did not react at all.

Egyptian Aedes mosquitoes showed a strong tendency toward this compound and even flew towards it in an experiment carried out in a wind tunnel. It showed that the canal, endocrinal, and glomerular H activity stimulated by these compounds are fundamental to how mosquitoes find human hosts.

“Amazingly, there is only one glomerulus whose activation pattern is specific to humans,” Dignaro said. “I thought there would be more.”

However, glomerulus H probably does not work entirely separately. According to Duvall, in addition to the neurons the researchers analyzed, mosquitoes have other sensory systems that detect chemicals that help mosquitoes find a host. Glomerulus H appears to be just one of the significant drivers of AIDS-Egypt human hunting behavior.

The authors did not test whether inhibiting glomerular H activity would shift mosquito preference from humans to animals, but this could be an exciting topic for research. “In theory, scientists could create chemical formulas that reduce glomerular H activity and increase the effectiveness of insect repellents,” Dignaro said. Zhao said his colleagues are working to produce such compounds.

Another potential application of this research is to inhale insect repellents or chemicals that could be used as bait to keep mosquitoes away from humans and trap them in traps, Duvall noted. Zhao et al.

They have patented their shop-and-canal combination and hope to use it.

Zhao speculates that other species of mosquitoes that use humans as their primary hosts may also show similar brain activation patterns in response to human odor.

“It will be interesting to look at other species that prefer humans, such as the Anopheles mosquitoes that transmit malaria, or the species that prefer other hosts, such as the Colex mosquitoes, which prefer birds,” Duvall said.