Ninety years ago it was discovered that mosquitoes track us down at night by responding to the smell we as humans produce. Since then, many studies have focused on identifying the nature of the chemicals we produce with the aim to use them to lure mosquitoes to trapping devices, thereby interrupting bloodfeeding and thus transmission of diseases like malaria. But why is there still no trap available for use in the developing world where malaria hits hardest?
A major complication is the fact that the search for active chemicals is like searching for a needle in a haystack. Humans produce several hundred organic compounds (from the skin and exhaled breath) and it has proven difficult to identify the ones that really matter. In the 1960s, research commenced in Gainesville Florida to identify attractants for the yellow fever mosquito Aedes aegypti. Since the late 1980s research on anopheline olfaction became fashionable as a novel means to interrupt disease transmission through trap development. Methods to determine if a mosquito detects a chemical were developed (electrophysiology) and high through-put systems followed in recent years. Although there is still no trap, two recent publications report hope that in due course this may change.
First, Niels Verhulst and colleagues reported an intriguing development. Although the possible role of skin biota (skin bacteria) has been published before, he was the first to succeed in attracting Africa’s main malaria vector, Anopheles gambiae sensu stricto, to the scent produced by skin bacteria only. In other words, he succeeded in attracting this mosquito, which has a strong preference for biting humans, to bacteria that were isolated from the human foot and cultivated on growth medium (agar). Without the presence of a human. Think of it, it is not us that lure mosquitoes…. It is the microflora on our skin. What can we do with this?
1) Develop probiotics that compete with ‘attractant-producing’ bacteria (such as Staphylococcus epidermidis that produces attractants);
2) Develop ‘soaps’ that selectively remove the bacteria that produce attractants. These would not be repellents, they would be called ‘making-you-less-attractiveants’;
3) Develop bait systems (e.g. broths) that are based on bacteria and attract mosquitoes;
4) Develop transgenic bacteria that produce repellents on our skin and mask the production of attractants….
Second, Fredros Okumu and colleagues claimed to have found a blend of compounds for Anopheles arabiensis that is 3-5 times more attractive as a human being. That’s really something. Perhaps we are closer to having a blend, that can be used in a trap in or near every hut in Tanzania, than we thought.
Key is that Okumu’s research was undertaken in a semi-field system (a large outdoor screened cage), which facilitated high through-put of compounds or blends thereof. Much more emphasis on testing of compounds in field settings should bring us closer to a trap over the next few years. The paper in PLoS ONE then details the results of an experimental hut study that is pretty convincing.
But there is more that needs done. We need a cheap source of carbon dioxide as well. And here Wolfgang Schmied has come up with a great idea – using locally available resources – to use Coca Cola bottles, with water, yeast, and sugar. The result: carbon dioxide. The results have not been published yet.
Next, we need a very cheap trap that can hopefully run free of power or utilise a renewable energy source (solar panel). Goal: the trap should cost less than 1 dollar. Alas, this is an idea we submitted to Gates, but they did not like it...
Combining the studies above should, however, lead to enough creative ideas to tackle the long-standing dream of mass trapping malaria vectors.
Give us your idea...