Why some people attracting mosquitoes than others, Microbiology professor explains

Mosquitoes stink, as anybody who has spent a summer evening repelling them or a summer day removing their bites will attest. But a significant factor in the attraction of mosquitoes to us is the odour that we emit as humans.

By creating an ice-rink-sized testing area and pumping in various people's smells, scientists were able to identify the various compounds in body odour that attract these insects, according to a research paper released on Friday.

Being members of the fly family, mosquitoes often eat nectar. However, females getting ready to ovulate need something to eat containing more protein: blood.

In the best-case scenario, being bitten will just result in a red, itchy bump. However, due to the parasites and illnesses that these insects spread, mosquito bites often result in death. Malaria is among the most harmful of these illnesses.

Microscopic parasites that dwell in red blood cells are what cause malaria, a blood-borne illness. When a mosquito strikes a person who has malaria, the parasite is also sucked up with the blood.

The parasite, after growing in the mosquito's stomach, "will shift to the salivary glands, followed by something being discharged back out into the skin of another human host when the mosquito blood-feeds again," said Dr. Conor McMeniman, an assistant professor of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health and Johns Hopkins Malaria Research Institute in Baltimore.

Thanks to window screens, air conditioning, and advancements in drainage systems where mosquitoes' aquatic larvae may develop, malaria was eliminated in the United States during the previous century, but it is still a threat in a large portion of the globe.

The majority of fatalities from malaria occur in children under the age of five and also in pregnant women, according to McMeniman, the senior author of the new research that was published in the journal Current Biology.

"It causes a lot of distress throughout the world, and one of the driving forces behind this study was an attempt to understand how malaria-transmitting mosquitoes are finding humans."

Drs. Diego Giraldo and Stephanie Rankin-Turner, the study's initial authors and Bloomberg postdoctoral scholars, and McMeniman concentrated on Anopheles gambiae, a mosquito species widespread in sub-Saharan Africa. They collaborated with the Macha Research Trust in Zambia, which is run by Dr. Edgar Simulundu, a scientist.

"We were extremely inspired by the idea of creating a system where we could study the behaviour of the African malaria mosquito in a naturalistic habitat, reflective of its native home in Africa," said McMeniman.

The scientists also intended to investigate the mosquitoes' capacity to follow smells across a distance of 66 feet (20 metres), compare the mosquitoes' preferences for various human odours, and monitor them during the hours of 10 p.m. and 2 a.m., when they are most active.

The researchers built a screened space the size of a skating rink to check all three boxes. Six screened tents that served as the research participants' sleeping quarters were scattered around the facility's perimeter.

Long tubes containing the responses of the respondent's individual breath and body odours were used to pump air from their tents to the main facility, where it was warmed and carbon dioxide-baited to resemble a sleeping person.

The odours of the sleeping individuals then served as a banquet for the hundreds of mosquitoes in the main 20 by 20-metre facility. The insects' journey to the various samples was monitored using infrared cameras. (The mosquitoes used in the research were not malaria-infected and could not bite the people who were asleep.)

The researchers discovered that certain individuals are more likely to attract mosquitoes than others, which is something that many picnickers can attest to. Additionally, chemical tests of the tents' exhaust air identified the odour-producing elements responsible for the mosquitoes' attraction—or lack thereof.

The airborne carboxylic acids, such as butyric acid, a substance found in "stinky" cheeses like Limburger, were the ones that attracted mosquitoes the most. On human skin, microorganisms create carboxylic acids that are usually undetectable to humans.

While the mosquitoes were drawn to the carboxylic acids, another molecule called eucalyptol, which is found in plants, seemed to scare the insects away. A single specimen with a high eucalyptol content was thought to have been connected to one of the individuals' diets, according to the researchers.

Finding a link between the compounds found in various people's body odours and the fragrances that attract mosquitoes, according to Simulundu, was "very interesting and exciting."

"This discovery opens up possibilities for the creation of lures or repellents that can be employed as traps that interfere with the host-seeking behaviour of mosquitoes, thereby controlling malaria vectors in regions where the disease is endemic," said Simulundu, a research coauthor.

Neurobiologist Dr. Leslie Vosshall, vice president and chief scientific officer of the Howard Hughes Medical Institute and a non-participant in the research, expressed similar enthusiasm. She said, "I believe it's very intriguing research." This is the first time a scaled-up experiment of this kind has been conducted outside of a laboratory."

Vosshall studies a different kind of mosquito that transmits dengue disease, Zika, and chikungunya. She and her colleagues discovered in research published in the journal Cell last year that this particular kind of mosquito also hunts for the aroma of carboxylic acids generated by bacteria on human skin.

She said that it is advantageous that these two distinct species react similarly to chemical signals since it may make it simpler to develop traps or repellents for mosquitoes in general.

The study might not immediately have any relevance to how to avoid getting bit by insects at your upcoming BBQ. Vosshall said that even cleaning with unscented soap leaves behind the odours of nature that attract mosquitoes.

The current article, she said, "gives us some exceptionally effective clues regarding the techniques mosquitoes are utilising to hunt us, and being aware of what that is is vital for us when coming up with what we should do next."