Beer consumption increases human attractiveness to malaria mosquitoes

Abstract

Background: Malaria and alcohol consumption both represent major public health problems. Alcohol consumption is rising in developing countries and, as efforts to manage malaria are expanded, understanding the links between malaria and alcohol consumption becomes crucial. Our aim was to ascertain the effect of beer consumption on human attractiveness to malaria mosquitoes in semi field conditions in Burkina Faso.

Methodology/principal findings: We used a Y tube-olfactometer designed to take advantage of the whole body odour (breath and skin emanations) as a stimulus to gauge human attractiveness to Anopheles gambiae (the primary African malaria vector) before and after volunteers consumed either beer (n = 25 volunteers and a total of 2500 mosquitoes tested) or water (n = 18 volunteers and a total of 1800 mosquitoes). Water consumption had no effect on human attractiveness to An. gambiae mosquitoes, but beer consumption increased volunteer attractiveness. Body odours of volunteers who consumed beer increased mosquito activation (proportion of mosquitoes engaging in take-off and up-wind flight) and orientation (proportion of mosquitoes flying towards volunteers' odours). The level of exhaled carbon dioxide and body temperature had no effect on human attractiveness to mosquitoes. Despite individual volunteer variation, beer consumption consistently increased attractiveness to mosquitoes.

Conclusions/significance: These results suggest that beer consumption is a risk factor for malaria and needs to be integrated into public health policies for the design of control measures.

Figure 1. The bioassay.

(A) The two tents set up outdoors and connected to the two traps of the Y-olfactometer by lay-flat tubing, and the olfactometer room located between the two tents. (B) Fan drawing air from a tent to the olfactometer via lay-flat tubing. (C) The Y tube-olfactometer.

Figure 2. Beer consumption increases human attractiveness.

(A) Effects of beer (n = 25 volunteers) or water (n = 18 volunteers) consumption on mosquito activation, expressed as the proportion of mosquitoes caught in both traps out of the total number released in the downwind box of the Y-olfactometer. In parentheses are the total numbers of mosquitoes entering both traps. (B) Effects of beer (n = 25 volunteers) or water (n = 18 volunteers) consumption on the mosquito orientation, expressed as the proportion of mosquitoes caught in the odour-baited trap out of the total number retrieved from both traps. In parentheses are indicated the numbers of mosquitoes entering the volunteer odour-baited trap. Error bars show 95% confidence interval of the mean proportion. Asterisks indicate significant effect of treatments on the response variables (GLMM); ns  =  not significant; ***  = P<0.001.

Figure 3. Variation in human attractiveness.

(A) Activation scores for each volunteer before and after dolo consumption (n = 25 volunteers). (B) Activation scores for each volunteer before and after water consumption (n = 18 volunteers). (C) Orientation scores for each volunteer before and after dolo consumption (n = 25 volunteers). (D) Orientation scores for each volunteer before and after water consumption (n = 18 volunteers). For each panel, the volunteers are ranked from bottom (lowest score before drink consumption) to top (highest score before drink consumption).

Figure 4. Consistencies in human attractiveness over the first and second trial.

(A) Relationship between mosquito activation on the first and second trial. (B) Relationship between mosquito orientation on the first and second trial. Volunteers from the dolo group (n = 25) are represented by closed circles and those from the water group (n = 18) by open circles. The lines are the least squares regression lines.