Would you be ready to sleep peacefully in a tent near hundreds of mosquitoes? It is a surprising scientific experiment which has just taken place in Zambia. The results help to better understand how some mosquitoes can spot humans from very far away.
With the return of sunny days, they will return: mosquitoes. Humans do not all seem equal in the face of mosquito bites, whose very sophisticated detection system still intrigues scientists. In a new study, published on May 19, 2023 in the journal Current Biology and spotted by Gizmodo, researchers wonder precisely how mosquitoes manage to find us from so far away. Even when you are hundreds of meters away from their trunk.
In order to determine this, scientists have used drastic means. They used a outdoor ice rink sized testing arena in Zambia “, sums up a press release presenting the work. Mosquitoes were free to fly inside this giant cage. Tents have even been installed and connected to the giant trap: humans have spent a few nights there – fortunately, without ever being in direct contact with mosquitoes.
A giant feast for mosquitoes
This 1,000 cubic meter arena has allowed scientists to observe that human body odor is indeed a key element for mosquitoes when they spot humans over long distances. Certain components of body odor that remain suspended in the air would explain why some people are bitten more than others.
” This is the largest olfactory preference rating system for a mosquito in the worldaccording to one of the study’s authors, neuroscientist Diego Giraldo of the Johns Hopkins Bloomberg School of Public Health (Maryland, USA), quoted in the press release. It’s a very sensory-charged environment for mosquitoes. In concrete terms, the scientists installed spaced out landing zones heated to 35° C (the temperature of human skin) in the arena. During the night, 200 hungry mosquitoes were released into the cage. Using infrared cameras, the researchers were able to track how often mosquitoes landed on the landing zones, likely ready to bite.
Heated areas didn’t seem to particularly attract mosquitoes unless they also contained CO2 (carbon dioxide). However, human body odor was a huge attraction to mosquitoes, much more so than CO2 alone. To go further, the researchers then asked individuals to sleep around this mosquito arena for 6 nights, in the tents. Using air conditioners, the air from the tents, laden with elements released by humans in their sleep, was channeled to the arena and especially to the landing zones. Result: some individuals attracted mosquitoes much more than others.
The scientists then set out to analyze 40 chemical substances, all emitted by all human guinea pigs, but in different quantities. They thus discovered that the humans most attractive to mosquitoes emitted a lot of carboxylic acid (which would be produced in particular by microbes on the skin).
A mosquito vector of malaria
This work focuses on one group of mosquitoes in particular, Anopheles gambiae. This species is a vector of malaria, particularly in Africa. This deadly disease, transmitted by the bites of certain mosquitoes, is a real public health concern in the world. So much so that some specialists wonder if mosquitoes should not simply be eradicated. According to the World Health Organization, there were 619,000 deaths attributable to malaria in 2021. 95% of malaria cases were recorded in Africa that same year.
The Anopheles gambiae mosquito particularly likes to land on human skin in the hours before midnight, with olfactory clues to find its prey. ” Human scent plays a vital role in guiding […] host selection by this prolific malaria vector as it makes its way to humans, resulting in intrinsic heterogeneity in the risk of human bite sum up the authors of the study.
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