Beer Makes People More Attractive...

...to mosquitoes. That's the finding of a new study that helps explain why mosquitoes seem more attracted to some people than others. Researchers -- who focused on a malaria-endemic area of Burkina Faso -- found that volunteers who drank the local brew were more attractive to mosquitoes than volunteers who only drank water.

This study's goal was to understand how diet, beer in particular, impacts how attractive humans are to malaria's primary vector in Africa, Anopheles gambiae Giles sensu stricto -- or An. gambiae (or mosquito) for short. Diet is thought to be an important part of body odor, which has been shown to provide the female An. gambiae with an olfactory trail to human hosts. Therefore, diet may be an important factor behind variation in human attractiveness to mosquitoes -- and possibly malaria risk.

To test this idea, the study's authors randomly assigned 43 adult males to drink either beer or water. Participants in the beer group drank a local brew called dolo, a homemade concoction of fermented sorghum (reported to be the most widely consumed alcoholic beverage in Burkina Faso). The rest of the volunteers consumed a tall glass of tap water.

So far, so good. But how do you measure "human attractiveness" in the eyes or -- more accurately, the nose -- of a mosquito? (In other news, scientists have successfully transplanted mosquito 'noses' to frog eggs and fruit flies to study what odors set off mosquito olfactory receptors.)

Hungry mosquitoes were reared from a batch of field-collected An. gambiae and denied a "blood meal" prior to the experiment. Researchers set up two outdoor tents connected to a Y-olfactometer and created an air current between the tents and the olfactometer (check out the photos online). After they were released into a downwind box connected to the Y-junction, mosquitoes could either choose to fly upwind toward either the smelly participant tent, or toward a plain outdoor air tent (traps in the olfactometer prevented the mosquitoes from escaping).

The attractiveness of each shirtless participant was tested twice, before and after consuming water or beer. "Attractiveness" was measured according to "activation" (how many mosquitoes flew upwind toward the traps vs. remained in the downwind box) and "orientation" (how many mosquitoes chose the smelly participant path vs. the outdoor air path).

Results indicated that mosquitoes only preferred human-infused air when the humans were beer drinkers. Water consumption had no effect on activation or orientation, both of which were enhanced by beer consumption. Other factors, such as carbon dioxide and body temperature, had no effect.

What does this mean? A crackdown on beer consumption in malaria-endemic areas?

Probably not. While the authors do point out that alcohol consumption contributes to the global burden of disease, and that at a certain level alcohol consumption can suppress one's immune system, this study only suggests that human odors produced by beer consumption can help us understand why biting patterns vary. Ultimately, this knowledge could inform the development of targeted interventions that focus on the favored victims of mosquitoes, helping to control the spread of malaria.

As a side note, if I were on the Institutional Review Board, I would have argued for a wait-list control design. This would have allowed the water drinkers to receive the treatment (a beer) after the experiment concluded -- you know, in the interest of fairness.
(h/t: Malaria Matters)

Photo Credit: garromeister