Unwashed socks could be antidote to mosquito bites

By Maore Ithula

A Kenyan scientist has invented a mosquito bait incorporating worn socks and fermenting yeast in a sugary solution.

Dr Richard Mukabana, the inventor of the special insect snare, says the discovery was made while testing various ingredients for making bait that would help lure the little blood-sucking parasites away from humans.

The researcher, who is an insect scientist based at the International Centre of Insect Physiology and Ecology (ICIPE's) the Mbita Point Station, says one of the latest survival techniques that the insect has developed over time is staying outdoors, rendering treated bed nets and indoor spraying useless.

Now the researcher had to get outdoors with a snare.

The report of his research was published in Malaria Journal on October 25, last year.

Exhaling skin

So how does Mukabana’s new invention work? The researcher says that it is long established that carbon dioxide that forms part of the breath exhaled by humans and other boned animals lays an important role in helping any blood-sucking insects to locate them.

The Anopheles Gambiae mosquito is one such creature that relies on the gas to locate its prey, Mukabana points out in his report.

Speaking to The Standard last week, the researcher said: "To locate us, mosquitoes follow the carbon dioxide we emit from our skin and exhale in our breaths. They then suck blood from us during and/or after which they transmit diseases like malaria and dengue into our bodies."

For this reason, the scientist confides, for a long time scientists have been using traps that are baited with industrially-produced carbon dioxide to capture mosquitoes for study.

But since mosquitoes are switching to waging their attacks on humans outdoors rather than indoors, and the prices of industrially produced carbon dioxide is way out of reach for the poor – who are the most vulnerable to the disease — Mukabana set out on a mission to search for, develop and/or adopt any existing method of producing carbon dioxide cheaply.

This is how the researcher settled on using the readily available baker’s yeast, sugar and water. When these three are mixed, he says, the sugar starts fermenting thereby releasing a lot of carbon dioxide.

Interestingly, the ‘by-product’ in this process is alcohol, thus complicating the whole process a little further.

But while the scientist is still scratching his head, as he broods on how to circumvent this challenge, he soldiers on to elaborate on where, how and when a worn pair of socks becomes important in the set up of ensnaring mosquitoes.

Mbita point

He says: "After a mosquito gets in your vicinity, the insect almost always goes for your feet."

Why is that so?

He says the feet of humans produce volatile compounds which contain some complicated carboxylic acids that again attract the species of mosquitoes that transmit malaria.

Having assembled his apparatus at ICIPE’s Mbita Point field station where the study is being conducted, the scientist went on to try his invention at Lwanda Nyamasari village, Homa Bay, Vihiga County.

Here, he baited some traps with the usual, industrially produced carbon dioxide.

He then baited others with carbon dioxide produced by fermentation when yeast is mixed with a sugar solution.

Both options were tested in a variety of settings including ‘semi-field’ trials – enclosed simulations of natural mosquito ecosystems, and full field trials — where traps were hung under the eaves of four huts in whose occupants were sleeping under bed-nets.

Nylon socks that had been worn (but not washed to ensure they retained human foot volatiles) by Mukabana and a fellow scientist were added to some of the traps while clean nylon socks were added to others as controls.

Worn socks

The top performing traps were those containing a combination of carbon dioxide derived from the yeast mixture and worn socks.

In the semi-field trials, unbaited traps caught only five per cent of the mosquitoes that were released.

And where the bait was worn socks alone only 43 per cent of the insects released were ensnared while the combination of a worn sock and yeast-produced carbon dioxide caught nearly 80 per cent of released mosquitoes.

The scientist thinks that the yeast may also release other gases in addition to carbon dioxide when it ferments.

"If I am right in my hypothesis, then other gases that are produced during fermentation could be also produced by bodies of the human being," he said.

Traps made using socks and yeast solution could, he says, significantly reduce costs and allow sustainable mass application of odour-baited devices for mosquito sampling in remote areas.

While producing carbon dioxide from yeast using a bottle of sugar and water is easy and possible in every African home, more research is needed to determine exactly what chemicals from the human scents attracted mosquitoes, says the researcher.

Mukabana’s research is funded by the Foundations for the National Institutes of Health (FNIH), a granting agency contracted by the Bill and Melinda Gates Foundation.