Researchers hope that if the strategy works, it will eventually complement insecticide-treated bed nets as a low-tech way to prevent malaria, which kills nearly 900,000 people a year worldwide, most of them children.
“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.
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.
The bait-and-kill strategy is a new one in malaria prevention efforts.
Normally, attempts to prevent malaria by controlling mosquitoes, known as vector control, have aimed at driving the insects away from people or killing them once natural attraction has brought them into proximity.