Why Mosquitoes Are More Attracted to Some People Than Others

For many people, mosquitoes are simply irritating and unpleasant. If that is the extent of your experience with them, you may be fortunate.

Mosquitoes are in fact the deadliest animals in the world, owing to their unmatched capacity to transmit a wide range of dangerous illnesses, including malaria, dengue fever, West Nile virus, and others.

This vector is estimated to cause more than 1 million human deaths each year. Understanding how and why mosquitoes locate us is therefore an extremely important area of research.

A new study published in iScience brings scientists a little closer to explaining why mosquitoes can appear unusually drawn to certain people while largely passing over others.

How mosquitoes choose their human hosts

Scientists at Florida International University (FIU) led an experiment involving 119 volunteers in Miami. Each participant placed an arm into a lengthy tube known as an olfactometer.

Researchers then released three mosquito species at the tube's opposite end - Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus - to assess which insects were attracted to which participants.

Mosquitoes are already known to respond to human smells, alongside many other inadvertent cues. However, precisely why small variations in body odour change a person's appeal to mosquitoes has remained difficult to establish.

One reason is the complex nature of human body odour. Odourless substances secreted by the skin are converted into gases known as volatile organic compounds (VOCs) through interactions with bacteria in the skin microbiome.

Scientists believe there are more than 1,000 VOCs on human skin, many of which need additional investigation. This makes it challenging to determine exactly how particular chemicals correspond with particular smells.

There are also around 3,600 recognised mosquito species, and each has probably developed somewhat distinct scent preferences. As a result, much remains unknown about the way mosquito attraction to scent operates.

"It has become increasingly clear that there is a connection between human skin microbes and/or odors when mosquitoes target individual humans," the research team, led by senior author and FIU neurogeneticist Matthew DeGennaro, explains in its paper.

"Although previous studies have compared the attraction of different mosquito species with individuals, cross-comparing attraction rates of multiple mosquito species to individual human volatilomes and skin microbiomes, to our knowledge, has not been previously accomplished."

Mosquito attraction differed between species

In the olfactometer trial, DeGennaro and colleagues found that Ae. aegypti was marginally more attracted to male participants than female participants. The other two tested species, however, showed no apparent preference.

The team also found that particular volunteers appeared more appealing to certain mosquito species. This did not mean that those participants were reliably more attractive to all three species.

Likewise, some volunteers seemed to have low attraction for one or more mosquito species, but were not consistently low-attraction across every one of the three species in the experiment.

There were slight correlations between the people that attracted Ae. aegypti and Ae. albopictus. Overall, though, the researchers report that each mosquito species seemed to favour a distinct group of participants.

For VOCs collected from volunteers' arms, Ae. aegypti and Cx. quinquefasciatus appeared to favour people with low concentrations of volatiles linked to low attraction. This suggests the mosquitoes may avoid certain VOCs when choosing where to land.

In contrast, Ae. albopictus seemed to target particular odour compounds that were attractive to it.

Skin bacteria linked to higher mosquito attraction

Across the 119 participants, the researchers identified 246 separate bacterial taxa. The team was surprised, however, to find that every participant's microbiome had only one bacterial species in common.

Although each mosquito displayed varying preferences for the bacterial types to which it appeared attracted, the results ultimately indicated that three specific bacterial types were consistently favoured.

"Across Ae. aegypti, Ae. albopictus, and Cx. quinquefasciatus mosquitoes, we detected three core bacteria in common for high-attraction participants that were not found across the low-attraction core microbiomes," the study authors explain.

"These bacterial taxa, Co. kefirresidentii, Cu. granulosum, and Staphylococcus epidermidis, may broadly signal to mosquitoes the presence of an attractive host."

Much more research is still needed into the odour compounds and bacteria that influence mosquito attraction. Yet every finding brings researchers closer to learning how to reduce the danger posed by mosquitoes.

For instance, it may be possible to develop specialised insect repellents that discourage mosquitoes, or even alter the skin microbiome to make people less attractive to them.

The findings are reported in iScience.

This article was fact-checked by Rachel Garner and edited by Michael Irving. While we take pride in our process, we are only human. If you notice an error, please let us know.