Stinky socks are a hot commodity in Tanzania these days. Researchers there have discovered that the odor attracts malaria-transmitting mosquitoes at a rate four times greater than a human volunteer. The researchers are looking at ways to use the odor to trap and kill mosquitoes outdoors.
In the laboratories of the Ifakara Health Institute in Tanzania, beauty is in the nose of the beholder.
Researchers there have come up with a combination of acids, ammonia, carbon dioxide, and other components from the human body that simulate a scent repulsive to humans but delicious to malaria-transmitting mosquitoes.
And that scent is strongest on what we wear on our feet.
Dr. Fredros Okumu is principal investigator of the Ifakara Health Institute’s Outdoor Mosquito Control project.
“If you are wearing socks, the things that come off your skin can be trapped onto the sock fabric. Even if you remove the sock, you can still put this sock in a mosquito trap and the mosquitoes will still target it thinking that it is you,” Okumu said.
Dr. Okumu explains that, thanks to the widespread use of bednets, insecticides, drugs, and rapid testing kits, malaria transmission has dropped substantially in sub-Saharan Africa, by as much as 50 percent in some countries.
But, he says, a substantial amount of malaria is still being transmitted outside the home, far from bednets or other protections.
“We went out there and constructed physical devices, and these physical devices, in there we put a synthetic attractant, or we put dirty socks. We showed that we could actually kill 74 to 95 percent of all the wild mosquitoes that visited our devices,” Okumu said.
Mosquitoes lured into this trap are exposed to a chemical or fungi agent. The insects die anywhere from 24 hours to five days later depending on the agent.
To test the effectiveness of the stinky sock odor, researchers constructed experimental houses in villages in southeastern Tanzania. Male volunteers slept in some of the houses, while the synthetic stinky-foot odor was placed in other houses.
“The synthetic attractant that we made on the basis of the sock science actually proved to be four times more attractive to mosquitoes than real humans,” Okumu said.
In some cases, the mosquitoes picked the house they would fly to from up to 110 meters away.
Researchers estimate that at least 20 of the dirty-sock devices are needed to protect every 1,000 people. The devices are estimated to cost up to $27 a year including maintenance.
Dr. Okumu says the first clue that smelly socks might be attractive to mosquitoes came from an experiment in the 1990s, when a naked male researcher stood in a dark room containing mosquitoes. He mapped out where the insects bit him, which was mostly on the legs.
The project has been granted almost $800,000 in additional funding for the next two years from the Bill and Melinda Gates Foundation and a Canadian group called Grand Challenges Canada.
Researchers have several goals within the next two years: to improve previous prototypes; to estimate the reduction in malaria transmission through the use of these devices; and map out specific locations in villages where mosquitoes are most abundant.
Fellow malaria scientists have said there is potential in the research.
Dr. John Vulule is chief researcher at the Kenya Medical Research Institute. He says similar studies were conducted in the Netherlands.
“Clearly, there is something attracting mosquitoes. There is the smell of the dirty socks. People talk about the cheese-like smell in the toes,” Vulvule said.
Dr. Vulule says that what is unique about this latest research is that it connects attracting mosquitoes with killing them, acting as a form of vector control for the transmission of malaria.