Oh the great outdoors, a time to get away from technology, to breath in the fresh air and ultimately relax. That is until you hear that high pitch buzz of the mosquitoes; those little bugs have sucked the joy out of more than one perfectly pleasant summer night.
Anyone who’s sat around a campfire, or has eaten outside on a muggy summer night knows mosquitoes have a preference for certain people. There’s always somebody getting ‘eaten alive,’ while others are not bothered by the little bugs. My sister was always getting attacked growing up, and believe me, I’ve had my fair share of bug bites and lack of sleep due to the incessant buzzing of a mosquito, but this was nowhere near the suffering my sister had to endure when it came to mosquito bites.
Fortunately, in my family “annoying” is all mosquitoes have been; no one’s ever contracted a disease from these sometimes deadly vectors.
Mosquitoes can transmit a number of diseases such as EEE, malaria, leishmaniasis, river blindness and West Nile virus just to name a few. Although there is certainly a MicrobiGals article in these diseases, today we are going to talk about your skin microbiome.
Turns out that mosquito preference is in part due to your microbes and the chemicals they release on your skin. There are over 3,000 different mosquito species with 176 of them being found in the United States alone. Many of these mosquitoes, including Anopheles gambiae (a.k.a the major malaria vector), are guided to hosts through odor. Human sweat, when it is first released, is in fact actually quite odorless and mosquitoes are not as attracted to it. However, when sweat is mixed with volatiles (tiny molecules) produced by skin bacteria, an odor is produced that mosquitoes have evolved to recognize as ‘lunch’.
Microbes are to blame for a number of foul smells produced by the human system: Bacillus subtilis is what gives your feet that ripe smell, Corynebacteria in your armpits produce androsterone sulphate, which is not a pleasant smell, and Corynebacteria, along with Staphylococci, help produce volatile fatty acids which, when smelled, we call sweat.
These microbes are hanging out on your skin all the time. However, the specific strain and abundance differs from person to person and thus the quantity and kinds of volatiles is unique to each person. So while sweat universally smells bad, we all smell bad in our own unique and special way. Researchers have found that Corynebacterium minutissimum produces volatiles that are more attractive to mosquitoes when compared with 4 other common skin microbes.
But, your skin microbes are so important, so don’t cover yourself with antimicrobials just yet (or never, just don’t do that). Humans and their microbes have been evolving together for thousands of years, each helping the other out. While some volatiles produced by skin microbes attract, others can repel.
Research into microbial volatiles is still in its infancy. There are thousands of different chemicals that belong to this class, many of them we have no idea what their role is. There are well over 500 compounds that are excreted from the human skin and exist in mixed environments, creating unique odor profiles which adds to the complexity. While we often attribute seeing and hearing as the more important sense, smelling is vital to ecology.
Mosquitoes can distinguish a number of smells we don’t even sense. To date, we know of over 114 chemicals that convey a signal to mosquitoes. These chemicals dictate the mosquitoes behavior such as when to mate, to lay eggs, and to feed; their lives are controlled by these smells. With over 3000 species and well over a 100 different chemicals, which can be combined in a plethora of ways, it can be very challenging to understand mosquitoes behavior enough to manipulate it.
Knols group conducted a clever experiment where they set up traps for the mosquitoes; just like a mouse trap they put cheese in it, specifically Limburger cheese. Why you may ask? Because Limburger cheese smells like your feet (not sure I’d want to eat this cheese, but hey try everything once right?).
This cheese smells like your feet because it contains Staphylococcus epidermidis, similar to the microbes that live in between your toes. The traps that contained the cheese trapped significantly more mosquitoes than control traps.
With new technologies such as gas chromatography-mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC) and electroantennographic detection (GC-EAD), scientists have never been in a better spot to discover which scents attract and which repel our annoying and dangerous mosquitoes.
If scientists can distinguish attractive and repellent volatile compounds, we can come up with new and natural remedies to mosquito bites either by attracting them away from human populated areas or to repel them from individuals.
Until then, try and protect yourself from mosquito bites, either by bug spray, bringing along a more attractive friend or setting up a cheese trap. Stay safe out there!