() — Anyone who has spent a summer afternoon swatting away mosquitoes, or a day scratching their bites, will agree: mosquitoes are the worst. But the odors that we humans produce are a big part of what attracts mosquitoes to us.
In a study published Friday, scientists helped determine the various body odor chemicals that attract these insects by building a test area the size of an ice rink and introducing the odors of several people.
Mosquitoes belong to the fly family and most of the time they feed on nectar. However, females preparing to produce eggs need an extra protein meal: blood.
At best, a bite will only leave you with a red, itchy bump. But mosquito bites often turn deadly because of the parasites and viruses they carry. One of the most dangerous diseases is malaria.
Malaria is a blood-borne disease caused by microscopic parasites that take up residence in red blood cells. When a mosquito bites a malaria-infected person, it sucks in the parasite along with the blood. After developing in the mosquito’s stomach, the parasite “migrates to the salivary glands and is then spat back onto the skin of another human host when the mosquito resumes blood feeding,” explains Dr. Conor McMeniman, associate professor of microbiology. Molecular and Immunology from the Johns Hopkins Bloomberg School of Public Health and the Johns Hopkins Institute for Malaria Research, in Baltimore.
Malaria was eradicated in the United States in the last century thanks to window screens, air conditioning, and improvements to drainage systems where aquatic mosquito larvae can thrive, but the disease remains a danger to much. of the world.
“Malaria continues to cause more than 600,000 deaths a year, mostly in children under 5 years of age, and also in pregnant women,” says McMeniman, lead author of the new study published in the academic journal Current Biology.
“It inflicts a lot of suffering around the world, and part of the motivation for this study was to really try to understand how the mosquitoes that transmit malaria find humans.”
McMeniman, along with Bloomberg postdoctoral researchers and study first authors Diego Giraldo, Ph.D., and Stephanie Rankin-Turner, Ph.D., focused on the Anopheles gambiae, a species of mosquito found in sub-Saharan Africa. They associated with the Macha Research Trust of Zambialed by Dr. Edgar Simulundu, Scientific Director.
“We were very motivated to develop a system that would allow us to study the behavior of the African malaria mosquito in a habitat that mirrored its natural habitat in Africa,” explains McMeniman. The researchers also wanted to compare the olfactory preferences of mosquitoes among different humans, observe the insects’ ability to track scents at distances of 20 meters, and study them during their most active hours, between 10 p.m. and 2 a.m. .
The researchers set up a screen the size of a skating rink to help understand how the mosquitoes that transmit malaria find humans. Credit: Julien Adam
To meet all of these requirements, the researchers created a sheltered facility the size of a skating rink. On the perimeter of the facility were six tents with mosquito nets where the study participants would sleep. Air from the tents, containing the participants’ characteristic breath and body odor, was pumped through long tubes to the main facility on absorbent pads, heated and infused with carbon dioxide to mimic a sleeping human.
Hundreds of mosquitoes in the main facility, 20 by 20 meters, then received a buffet of the odors of the sleeping subjects. Infrared cameras followed the movement of mosquitoes towards the different samples. (The mosquitoes used in the study were not infected with malaria and could not reach sleeping humans.)
The researchers found what many picnickers can attest: Some people attract more mosquitoes than others. What’s more, chemical analyzes of the air in stores revealed the odor-causing substances that did or did not attract mosquitoes.
Mosquitoes were more attracted to carboxylic acids in the air, including butyric acid, a compound found in “stinky” cheeses like Limburger. These carboxylic acids are produced by bacteria on the human skin and are usually not perceptible to us.
While the carboxylic acids attracted mosquitoes, another chemical called eucalyptol, found in plants, seemed to deter them. The researchers suspected that a sample with a high concentration of eucalyptol could be related to the diet of one of the participants.
Simulundu said that finding a correlation between the chemicals in different people’s body odors and the attraction of mosquitoes to those odors was “very interesting and exciting.”
“This finding opens up approaches to developing lures or repellents that can be used in traps to alter the host-seeking behavior of mosquitoes, thereby controlling malaria vectors in malaria-endemic regions,” said Simulundu, co-author of the study.
Dr. Leslie Vosshall, a neurobiologist and vice president and chief scientific officer at the Howard Hughes Medical Institute, who was not involved in the study, was equally enthusiastic. “I think it’s a very interesting study,” she said. “This is the first time that such an experiment has been done on this scale outside of the laboratory.”
Vosshall investigates another species of mosquito that spreads dengue, Zika and chikungunya. In a study Published last year in the academic journal Cell, she and her colleagues discovered that this species of mosquito also seeks the scent of carboxylic acids produced by bacteria on human skin. The fact that these two different species respond to similar chemical signals is positive, she says, because it could make it easier to create mosquito repellents or traps in general.
The research may not have immediate consequences for avoiding bug bites at the next barbecue. Vosshall noted that even scrubbing with unscented soap doesn’t remove natural odors that attract mosquitoes. However, he noted that the new work “gives us some really good clues about what mosquitoes use to hunt us, and understanding what it is is essential for us to take the next steps.”
— Kate Golembiewski is a Chicago-based freelance science writer with a passion for zoology, thermodynamics, and death. She hosts the comedy show “A Scientist Walks Into a Bar.”
