Lou Mollock figures it’s the islander blood. The Coppin State University student’s mother is Jamaican. Perhaps that’s why mosquitoes feast on the student during summer hikes in Baltimore County.
“Maybe it’s an islander-on-the-wrong-side-of-the-world-type thing,” Mollock said.
Just up the trail at Lake Roland Park, Kisha Edwards doesn’t understand the fuss. She can finish her route as a mail carrier in Catonsville without one bite.
“It might be the blood type? I don’t know. They don’t bother me at all,” Edwards said.
The seemingly capricious tastes of mosquitoes confound us. Do they prefer sweet skin? Type O blood?
A new study in Current Biology by an assistant professor at the Johns Hopkins University examines a key factor that attracts mosquitoes to some people over others: body odor.
Mosquitoes prefer men and women with high levels of three common, natural compounds with smells most closely associated with rancid butter, cheese and, well, vomit.
“We all emit our own sort of bouquet of 300 airborne chemicals that emit from the skin and the breath, that dissipate into the air,” said Conor McMeniman of the Johns Hopkins Malaria Research Institute.
Maryland reports a handful of cases annually of the mosquito-borne West Nile virus, but the bugs are generally just a nuisance here. Not so in Southern Zambia, where McMeniman conducted the study and the home to the malaria mosquito. Malaria kills hundreds of thousands of people a year, and more than 90% of these deaths are reported in Africa, according to the World Health Organization.
Researchers have long sought ways to protect people in Africa from mosquitoes. If they can identify what attracts mosquitoes to people, they can reduce the allure. Or they can build and bait traps to save lives.
The study began from McMeniman’s hypothesis that mosquitoes have evolved to detect smells distinct to the human body. Only, do they prefer the smell of some people over others?
In Zambia, McMeniman and the research team erected a 65-foot-long screened cage to hold a swarm of mosquitoes. They assembled small, one-person tents outside and connected the tents to the cage with aluminum ductwork. In the tents, people went to sleep and fans blew their breath and body odors into the mosquito cage. The ductwork emptied onto warmed landing pads. Researchers used infrared light to track the mosquitoes.
First, they tested the system and blew clean air into the mosquito cage. The bugs seemed uninterested until they pumped in the test subjects’ breath and smells.
“Human scent really draws mosquitoes,” McMeniman said. “A warm thing by itself attracted very little to no mosquitoes.”
McMeniman observed the mosquitoes preferred the same people night after night. He calls these people “mosquito magnets.”
The people who attracted the most had the highest levels of smelly natural compounds called carboxylic acids. These compounds are produced naturally by bacteria on the skin and present in sweat and oils. The “mosquito magnets” showed high levels of three acids in particular: butyric acid (vomit smell), isobutyric acid (rancid butter) and isovaleric acid (cheese).
Few mosquitoes were attracted to the odor of sleepers with high levels of similar natural compounds that smell like plants: eucalyptus, citrus and sage.
McMeniman wants to continue his research to examine how diet affects body odor and, in turn, individual mosquito appeal. For now, he encourages Marylanders to take routine precautions against mosquitoes this summer: bug spray, window screens, ceiling fans, air conditioning.
If you eat too much cheese, will mosquitoes come for you?
“It’s too early to make those associations, although they are fun to think about,” McMeniman said. He paused. “I’ll still be eating cheese. I love cheese.”