Mosquito magnet

By Noralyn Dudt

A mosquito bites you while sitting outside in the yard and you wonder why the fellow sitting next to you does not get a bite?  Have you ever thought that you might be one of those mosquito "magnets?"

According to the journal Cell (a peer-reviewed scientific journal that publishes research papers across a broad range of disciplines within  the life sciences), mosquito-borne diseases impact about 700 million people per year, and experts expect that number to increase as global temperatures rise. The A.aegypti mosquitoes are known to live in tropical or subtropical climates, but the insect has adapted  and now breeds in the cooler regions of the United States.

Some people are "magnets" for mosquitoes, emitting a tantalizing combination of chemicals that invites the pesky insects to dine on them. Scientists have known that mosquitoes have a preference for some humans over others but the reason wasn't fully understood. A laboratory at Rockefeller University conducted studies and research to find out why some people seem to smell better to an A.aegypti mosquito than others. The researchers found that people who have higher levels of certain acids on their skin are 100 times more attractive to the female Aedes aegypti, the type of mosquito responsible for spreading diseases such as dengue, chikungunya, yellow fever and Zika.

The experiment was conducted not in a room full of mosquitoes, fortunately.  Instead, the researchers collected the natural scent from people's skin by having them wear nylon stockings on their arms. They cut the stockings into two-inch pieces and placed two pieces of the fabric behind two separate trap doors in a clear plastic box where dozens of mosquitoes were flying around. The researchers then opened the traps and the insects would choose to fly  to the bait—the stockings—behind the first or the second door.

The researchers conducted a round-robin style tournament and counted each time an insect was drawn to a particular sample,  much like the points in a basketball game. One of the samples, described as being from "subject 33," emerged as a favorite of the insects.

The study concluded that people like subject 33, who have higher level of compounds called carboxylic acids on their skin, are more likely to be mosquito "magnets."

All humans produce carboxylic acid through sebum, a waxy coating on their skin.  The sebum is then eaten by the millions of beneficial microorganisms that colonize our skin to produce more carboxylic acid. In copious amounts, the acid can produce an odor that smells like cheese or smelly feet. That smell appears to attract the female mosquitoes on the hunt for human blood.

It must be noted that the nylon stockings used in the study didn't actually smell like sweat, the report says. The mosquitoes are incredibly sensitive to human odor, and neither perfume nor cologne can cover it up. The experimental study was conducted over the course of three years, and the same people continued to appeal to mosquitoes regardless of what they ate that day or whether they changed their soap or shampoo.

What was not answered in the study was why some people have more carboxylic acids on their skin than others. The scientists said that the composition of the skin microbiome is unique in every individual. "Everybody has a completely unique village of bacteria living on their skin," the lead researcher said.

The scientists' advice to people who don't want to be a "meal" for mosquitoes, is to take a shower before spending a significant amount of time outside. It would reduce "all those juicy compounds" that are on the skin, especially around the feet with their unique odors.

The future lies in figuring out how to "manipulate" the odors that originate from the skin, and potentially the bacteria living there. For instance, scientists may be able to develop a probiotic skin cream that interferes with or reduces the levels of certain byproducts, which could make a person less attractive to mosquitoes. To develop that perfect repellant however is to have a complete understanding of what makes people a mosquito magnet.

 

(Noralyn Onto Dudt is from North Bethesda, Maryland.)