Using smelly socks to attract mosquitoes — and combat malaria

As it turns out, smelly socks can do more than stink up the laundry basket.

In an effort to combat malaria, researchers in Tanzania are developing devices that use human foot odor to lure mosquitoes. By targeting malaria transmission outdoors, the devices would complement other malaria-reducing methods, such as bed nets and indoor insecticide sprays, which protect people in their homes.

I spoke recently with Dr. Fredros Okumu of the Ifakara Health Institute. Below are excerpts from our interview.

You developed a device that uses human foot odor to lure mosquitoes. What does the device look like and how does it work?

We have two devices that we’re moving forward with. Both of them are essentially boxes. They’re made of materials that we can find in malaria-endemic countries, particularly in Tanzania where we’re working at the moment.

The first device is a box with a wooden framework and converse covering. It essentially looks like a miniature house. It allows in mosquitoes. They are attracted with a synthetic attractant or socks that we put inside the device. When the mosquitoes come into the device, either they can be trapped or they can be contaminated and left to fly away. If they are contaminated, they die within days.

The second device is much smaller. It’s a black box with landing surfaces on the sides. Inside we put a synthetic attractant, so mosquitoes think it is a human. When mosquitoes think it’s a human being, they land on its surfaces. Because they don’t find blood, they fly away shortly afterwards. Even if they fly away shortly afterwards, they carry with them a killing agent. We have tested two killing agents — a chemical insecticide and mosquito-killing fungi.

If you keep this device around people’s houses for a year or two, every night mosquitoes will be contaminated. We hope eventually we’ll be able to reduce the density and survival of malaria mosquitoes to such an extent that malaria transmission will be reduced to such low levels that we can start talking about malaria elimination in some of these endemic areas.

Why do you use foot odor to attract mosquitoes and how do you use it?

We knew mosquitoes could not see people. Instead, mosquitoes smell people. The important chemicals that attract mosquitoes are lactic acid from our sweat glands, triglycerides on our skin and carbon dioxide that comes off our breath.

Once we knew which chemicals would attract mosquitoes, we put the chemicals together in certain combinations to see if they would mimic a human being. We set up two experimental houses where human volunteers slept under bed nets. We had another two experimental houses where we put this synthetic mixture of chemicals. We counted the number of mosquitoes that entered these houses. The houses baited with the synthetic mixture were getting at least four times more mosquitoes than the houses baited with human volunteers. This was strong evidence that the synthetic mixture was not only mimicking humans, but was bringing in more mosquitoes. With our original grant from the Bill & Melinda Gates Foundation, we developed a physical device that used the synthetic attractant.

Socks tend to trap a lot of the chemicals that come off your skin. These chemicals remain on the sock for a long time. If you stick the socks inside a trap, you can attract mosquitoes. This is something scientists have known for a long time. We would like to pursue this technology further for the simple reason that it is easy to find this kind of smell, as opposed to a synthetic attractant.

Are the devices already being used in Africa?

This is still an early stage of development. We do not foresee these being used for the next two to four years. The work started one and a half years ago when we got $100,000 grant from the Bill & Melinda Gates Foundation. Now we have additional funding from the Gates Foundation, but also from Grand Challenges Canada. With this additional funding we’re moving on to try to make this a reality. We’re trying to do four things:

• Improve upon the prototypes of the devices we first made
• Measure the level of epidemiological impact we can expect from these devices
• Find the right place to put these devices
• Develop practical ways to implement this technology in rural areas

Photo, top: Anopheles Freeborni Mosquito pumping blood / Courtesy of CDC

Photo, bottom: Fredros Okumu