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Sunday, September 4, 2011

Smelly feet and Mosquitoes

Researchers in Tanzania are attempting to use dirty socks in order to lure mosquitoes to specially constructed traps where they are poisoned and quickly die.

In global public health, disease-fighting tools that are cheap, available and sustainable are the Holy Grail. It might be hard to top the one being tested in Tanzania as a way to prevent malaria: smelly socks.
Every year almost 800,000 people, mostly children, die from malaria. Tanzania's Ifakara Health Institute has begun to develop a device that may help prevent malaria deaths in the developing world using the odor of smelly socks.

Researchers headed by Dr. Fredros Okumu know that mosquitoes are turned on by the scent of a smelly sock. The stinky device, which is a complement to bed nets and sprays, is placed outside of the home. Inside the device is smelly synthetic bait that attracts the disease carriers. Once the aroma attracts them they are trapped or poisoned and left to die.
“It’s a bold idea. Who would have thought there was a life-saving technology working in your laundry basket?” said Peter A. Singer, a physician who heads Grand Challenges Canada, a development agency of the Canadian government that is helping fund the research.
Experiments in three villages where people get about 350 bites a year from malaria-infected mosquitoes are using dirty socks to lure the insects into traps, where they become contaminated with poisons and ultimately die.
Researchers hope that if the strategy works, it will eventually complement insecticide-treated bed nets as a low-tech way to prevent malaria.
Previous lab studies have shown that smelly socks work well in attracting mosquitoes. Field experiments have shown that synthetic bait is more attractive than people, at least until the insects get close enough to realize there’s no blood waiting for them.
The new experiments, however, are the first head-to-head field tests of footwear vs. chemistry. The researchers hope the footwear wins.
“It is simply a cost issue and an expediency issue,” said Fredros O. Okumu, the Tanzanian entomologist leading the research. “Socks are more readily available, and you don’t have to mix any chemicals. It is the sort of thing that could be set up in a cottage factory.”
The traps are square boxes that look a little like commercial beehives. Some will contain the human-odor bait, which consists of simple chemicals (including lactic acid, ammonia and propionic acid) that are exuded by people, especially from the legs and feet. Some will contain socks worn for a day by adults. Others will contain cotton pads that schoolchildren will put inside their socks for a day and then deliver to researchers.
The researchers will compare the number of mosquitoes caught with each method.
Earlier work by Okumu and his colleagues at the Ifakara Health Institute in Tanzania showed that the chemical bait attracted four times as many mosquitoes as live people and that dirty socks worked just as well, at least in the lab. If the sock pads prove adequate, they will be the preferred bait.
The inside surfaces of some traps are coated with an organophosphate pesticide. Mosquitoes that land there will die within 24 hours. Other traps contain a fungus that infects the insects and kills them in five days — roughly half the time needed for the complicated cycle that enables a newly infected mosquito to transmit the malaria parasite to a person.
Dr. Fredros Okumu's grant is funded by both Grand Challenges Canada and the Bill and Melinda Gates Foundation. It is expected that the device could be in use by the community within two years.

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