The Bite That Kills

Credit: CC

Credit: CC

Summer is finally here and for some of us, the sweat-inducing humidity and high electrical bills are the least of our worries. Mosquito bites are inevitable for nearly anyone who ventures outside, but unfortunately the blood-sucking insects display a definite preference for their victims. And while multiple bites can be an itchy nightmare for those that are allergic to mosquito saliva, bites are also deadly in many parts of the world. Mosquitos transmit malaria, encephalitis, heartworm, and West Nile virus; combined these diseases cause an estimated 1 million deaths around the world per year.

However some people are lucky enough to naturally avoid getting bitten, though the reasoning behind this is still unclear. While there have been a multitude of studies attributing ‘immunity’ to various causes, treatments stemming from these discoveries have yet to be established. Currently the most effective method of repelling mosquitos is N,N,-Diethyl-meta-toluamide (commonly known as DEET). DEET is thought to activate mosquito olfactory receptor neurons. And while DEET is extremely potent, it is toxic in higher concentrations and some mosquitos can also develop any immunity to the repellent. This makes mosquito research an active field, as identifying a natural repellent could be instrumental in protecting public health in malaria risk areas.

Research into what makes some people more attractive to mosquitos than others began in the early 1990s. Since then, mosquito attraction has been attributed to an individual’s ‘personal scent,’ though countless factors contribute to one’s scent and everything from genes to skin bacteria has been attributed to mosquito attraction, as well as stress levels. Unfortunately this means that a one-size-fits-all approach to preventing bites is not in the very near future, but we are still learning about new causes for attraction.

One of the older and more predominant theories on mosquito attraction is that they use carbon dioxide to detect their nearest meal. Female mosquitos (females need blood proteins to lay eggs) have specific nerve cells that allow them to sense sources of carbon dioxide. However these receptors are not specific for carbon dioxide, and also help mosquitos respond to the chemicals that comprise our personal scents. By blocking the carbon dioxide receptors, researchers have been able to also temporarily block detection of human skin odorants. Skin odor has been linked to mosquitos as well, with study results showing that odors are affected both by genes as well as skin bacteria. A 2011 study found that the diversity of skin bacteria could also be influential to mosquito preferences, as a less diverse microbial community is more attractive to malaria mosquitos. But it was recently found that odors emitted by bacteria are not the only features that draw in mosquitos. When researchers modified common skin bacterial species to prevent communication between cells, mosquitoes were less likely to be attracted to the mutant bacteria than the wild-type. This new discovery is exciting because it helps us understand the various mechanisms by which mosquitos sense their environment. Since it turns out that mosquitos depend on much more than carbon dioxide to sense prey, delving deeper into the sensing capabilities will help us develop more robust repelling methods.