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Why Are Certain Humans Mosquito Magnets?

Written by Nitin Sreekumar ‘25

Edited by Lisa Long '25

If you have ever visited or lived in an area plagued with mosquitos, you know that mosquitos do not treat all people equally. Some people get off without any bites while others are like magnets, attracting the entire population to them (1). What is behind the seeming pickiness of mosquitoes? While this may seem like a frivolous question, it may hold the key to designing more effective mosquito repellents and potentially save lives.


Aedes aegypti, a mosquito that has spread around the world, is a vector of numerous viruses that cause life-threatening diseases, such as dengue fever, chikungunya, Zika fever, Mayaro, and yellow fever. A single female mosquito can bite several humans during her lifetime and the mosquito can contract and spread disease. In fact, mosquitoes cause the most deaths of any animal, and still lead to the deaths of 725,000 people worldwide each year.

The accepted explanation for the mosquito magnet phenomenon is that different people's skin odors can affect how attractive they are to mosquitoes (2). Although female mosquitoes use CO2 and heat aid in the identification of warm-blooded creatures, skin odor notifies them when the target is a human (3). Human skin odor is a blend of many organic compounds, and those who are particularly attractive to mosquitoes may release additional chemicals. In contrast, less attractive people typically generate mosquito-repelling chemicals such 6-methyl-5-hepten-2-one, octanal, nonanal, decanal, and geranyl acetone (5). These substances each decrease insect flight activity with less attraction, indicating that some people may emit natural repellents that lessen their attractiveness to mosquitoes.


Maria Elena De Obaldia and her colleagues at the Rockefeller University in New York City studied this behavior by giving 64 participants nylon stockings to wear around their forearms for six hours in order to examine skin odor (6).Then, scientists offered mosquitoes a choice between two pairs of stockings and observed which ones they chose to land on. Next, they were able to pinpoint the substances on the wearers' nylon stockings that attracted mosquitoes more. They were able to distinguish nine of the compounds as straight-chain fatty acids. Fatty acids with greater than 10 carbons appeared to be enriched in the most highly attractive subjects. These included pentadecanoic acid, heptadecanoic acid, and nonadecanoic acid. Each person had an attractiveness score calculated by the researchers, and they discovered that the highest score was more than 100 times higher than the lowest. These differences remained consistent, even after more than a year.


The researchers also tested mosquitoes lacking the co-receptor Ir8a, which is expressed in the antenna and is required for detection of several acids, including lactic acid, a component of human sweat (7), In this study, researchers bred mosquitoes lacking the genes for certain smell receptors which retain strong attraction to humans but show deficits in discriminating humans from non-human animals (18). Although these insects were far less efficient at smelling human odor, they were still able to distinguish between people who scored well and poorly on the attractiveness scale. This shows that many genes have a role in assisting mosquitoes in locating their next meal.


Since a small percentage of humans are thought to be more frequently targeted in disease-endemic areas and act as a reservoir for infections, the attraction preferences of disease-vectoring mosquitoes have significant consequences for public health (9). In addition, new research has demonstrated that flavivirus infections change the microbiota of people and increase their attractiveness to mosquitoes (10). Further, studies on humans (11) and mice have shown that malaria infection increases the attractiveness of humans to mosquitoes by altering the chemistry of human skin odor, resulting in greater pathogen transmission.


In order to limit mosquito attraction to people and stop the spread of harmful diseases, it is important to understand the mechanical underpinnings of mosquito biting preferences. Knowing what makes a person a "mosquito magnet" will help logically design interventions, including modifying the skin microbiome, to reduce a person's attraction to mosquitoes. It would be possible to use resources to stop the spread of illnesses carried by mosquitoes more effectively if it were possible to predict which members of a community will attract mosquitoes.

 

References

[1] Konopka JK, Task D, Afify A, Raji J, Deibel K, Maguire S, et al. Olfaction in Anopheles mosquitoes. Chem Senses. 2021;46.

[2] Qiu YT, Smallegange RC, Van Loon JJA, Ter Braak CJF, Takken W. Interindividual variation in the attractiveness of human odours to the malaria mosquito Anopheles gambiae s. s. Med Vet Entomol. 2006;20(3):280-7.

[3] Zhao ZL, Zung JL, Hinze A, Kriete AL, Iqbal A, Younger MA, et al. Mosquito brains encode unique features of human odour to drive host seeking. Nature. 2022;605(7911):706-+.

[4] Gallagher M, Wysocki J, Leyden JJ, Spielman AI, Sun X, Preti G. Analyses of volatile organic compounds from human skin. Brit J Dermatol. 2008;159(4):780-91.

[5] Logan JG, Birkett MA, Clark SJ, Powers S, Seal NJ, Wadhams LJ, et al. Identification of human-derived volatile chemicals that interfere with attraction of Aedes aegypti mosquitoes. J Chem Ecol. 2008;34(3):308-22.

[6] De Obaldia ME, Morita T, Dedmon LC, Boehmler DJ, Jiang CS, Zeledon EV, et al. Differential mosquito attraction to humans is associated with skin-derived carboxylic acid levels. Cell. 2022;185(22):4099-+.

[7] Raji JI, Melo N, Castillo JS, Gonzalez S, Saldana V, Stensmyr MC, et al. Aedes aegypti Mosquitoes Detect Acidic Volatiles Found in Human Odor Using the IR8a Pathway. Curr Biol. 2019;29(8):1253-+.

[8] DeGennaro M, McBride CS, Seeholzer L, Nakagawa T, Dennis EJ, Goldman C, et al. orco mutant mosquitoes lose strong preference for humans and are not repelled by volatile DEET. Nature. 2013;498(7455):487-91.

[9] Harrington LC, Fleisher A, Ruiz-Moreno D, Vermeylen F, Wa CV, Poulson RL, et al. Heterogeneous Feeding Patterns of the Dengue Vector, Aedes aegypti, on Individual Human Hosts in Rural Thailand. Plos Neglect Trop D. 2014;8(8).

[10] Zhang H, Zhu YB, Liu ZW, Peng YM, Peng WY, Tong LQ, et al. A volatile from the skin microbiota of flavivirus-infected hosts promotes mosquito attractiveness. Cell. 2022;185(14):2510-+.

[11] De Moraes CM, Wanjiku C, Stanczyk NM, Pulido H, Sims JW, Betz HS, et al. Volatile biomarkers of symptomatic and asymptomatic malaria infection in humans. P Natl Acad Sci USA. 2018;115(22):5780-5.


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